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Sewage sludge ash (SSA) based P-fertilisers were produced by thermochemical treatment of SSA with Cl-donors at approximately 1000 °C. During this thermochemical process heavy metals are separated as heavy metal chlorides via the gas phase. Chromium cannot be separated under normal conditions. The risk of the development of toxic Cr(VI) during the thermochemical process was investigated. X-ray Absorption Spectroscopy measurements showed that SSA and thermochemically treated SSA with CaCl2, MgCl2 and NaCl contain Cr(III) compounds only. In contrast, treating SSA with elevated quantities of Na2CO3, to enhance the plant-availability of the phosphate phases of the fertiliser, developed approximately 10–15% Cr(VI). Furthermore, Raman microspectroscopy showed that using Mg-carbonate reduces the risk of a Cr(VI) development during thermochemical treatment. Additionally, leaching tests showed that only a Crwater solubility >10% is an indicator for Cr(VI) in SSA based P-fertilisers.
Sewage sludge has one of the highest phosphorus (P) recovery potentials of all waste materials.
Therefore, P-recycling from sewage sludge could contribute to closing the P-cycle. Recently, various thermal processes for P-recovery have been developed, but there is still a demand for information on the effect of different process parameters (e.g. additives and temperature) on P-speciation and especially on the fertilization performance. In the present study, two common methods (low-temperature conversion at 400–500 °C and thermochemical treatment at 950 °C) were investigated and combined to produce highly bioavailable P-fertilizers from two different types of sewage sludge based on chemical phosphorus precipitation (Chem-P) and enhanced biological phosphorus removal (Bio-P). The results of P-fractionation, X-ray diffraction analysis, and pot experiments with maize showed that Bio-P sludges attain high P-plant-availability after treatment at low temperatures (400 °C). In contrast, Chem-P sludges can adequately be treated at higher temperatures under reductive conditions with sodium additives to form highly bioavailable calcium-sodium-phosphate. Additionally, also highly heavy-metal contaminated sludges can be thermochemically treated at high temperatures to achieve the legal requirements for fertilizers.
Phosphorus (P) is an essential element for all forms of life and is applied as fertilizer in agriculture. The P availability for plants may be highly dependent on the chemical state of P in fertilizers and soils; however, the nature of this dependence remains obscure due to the limitations of generally applied wet chemical and instrumental analytical approaches. This paper focuses on recently developed infrared, Raman, ultraviolet and X-ray microspectroscopic techniques for the characterization of P in soil. Microspectroscopic techniques have the advantage that discrete P phases can be distinguished and characterized even if their mass fractions are very low. However, only small volumes of soil can be analyzed by microspectroscopic methods hence a combination of macro- and microspectroscopic techniques is a promising concept.
Determination of chromium (VI) in primary and secondary fertilizer and their respective precursors
(2017)
Hexavalent chromium species (Cr(VI)) are often carcinogenic, of high acute toxicity, highly mobile, and thus pose a severe risk to health and environment. Fertilizers usually contain significant amounts of chromium. Therefore, a reliable analysis of chromium and the fraction of Cr(VI) are crucial for safe use of fertilizers. This problem is expected to increase in the future, since more and more recycled fertilizers emerge due to increasing fertilizer demand and respective supply risks. However, existing analytical methods have been developed for conventional fertilizers and have to be tested whether they are suitable for the new materials. Thus, we performed a wet-chemical extraction for Cr(VI) on several matrices as well as respective quality control experiments including spiking with Cr(III) and Cr(VI)compounds. We found the Cr(VI) amounts to be below 2 mg/kg except for a thermally post-treated sewage sludge ash (SSA) that showed 12.3 mg/kg. The presence of organic matter e.g. in sludge or precipitated struvite caused a reduction of spiked Cr(VI) and thus no satisfying recovery for Quality control. Cr(VI) reduction was also observed for SSA, presumably due to the presence of Fe(II) compounds.
Even though the tested procedure can be hampered in some recycled fertilizer matrices, it might be adapted to be applicable also for these complex samples.
Pot experiments are often performed to analyze the plant-availability of phosphorus (P) in P-fertilizers. However, these experiments do not determine the P compounds present in the soil which are responsible for the yield increase. In order to better understand the results of pot experiments we analyzed the soils by P K-edge X-ray absorption near-edge structure (XANES) spectroscopy to determine the P species and unravel transformation processes. We carried out pot experiments with maize testing different waste water derived recycling P-fertilizers on an acidic and a neutral soil. Soils samples before sowing and after harvest were collected and prepared for analysis. A combination of macro- and µ-XANES spectroscopy was used to determine the chemical state of the overall soil P and to identify P compounds in P-rich spots localized by micro-X-ray fluorescence (µ-XRF). P K-edge macro-XANES spectroscopy detected organic P and/or P sorbed onto organic matter or other substrates in the unfertilized and fertilized soils. In addition, µ-XRF mapping in combination with P K-edge µ-XANES spectroscopy evidenced that some P phases present in recycling P-fertilizers (magnesium phosphate and calcium sodium phosphate) react with co-fertilized ammonium nitrate and form highly plant-available ammonium phosphates in the soil. In opposite, apatites were not affected by the presence of ammonium. Thus, for a boost of the plant-availability of P in recycling P-fertilizers these fertilizers should be directly co-fertilized with nitrogen (N) sources that contain a high amount of ammonium instead of nitrate. Possibly, a specific preparation of NP-fertilizers by granulation of recycling P-fertilizers with ammonium compounds and a nitrification inhibitor could enhance the plant-availability of the produced fertilizer whereby they become more competitive to commercially available NP-fertilizers based on phosphate rock.
Phosphorus-fertilizers from secondary resources such as sewage sludge ash (SSA) will become more important in the future as they could substitute conventional fertilizers based on the nonrenewable resource phosphate rock. Thermochemical approaches were developed which remove heavy metals from SSA prior to its fertilizer application on farmlands. We analyzed the chemical state of mercury and selenium in SSA before and after thermochemical treatment under different conditions for P-fertilizer production by X-ray absorption near edge structure (XANES) spectroscopy. In some incineration plants the mercury loaded carbon adsorber from off-gas cleaning was collected together with the SSA for waste disposal. SSAs from those plants contained mercury mainly bound to carbon/organic material. The other SSAs contained inorganic mercury compounds which are most probably stabilized in the SSA matrix and were thus not evaporated during incineration. During thermochemical treatment, carbon-bound mercury was removed quantitatively. In contrast, a certain immobile fraction of inorganic mercury compounds remained in thermochemically treated SSA, which were not clearly identified. HgSe might be one of the inorganic compounds, which is supported by results of Se K-edge XANES spectroscopy. Furthermore, the chemical state of selenium in the SSAs was very sensitive to the conditions of the thermochemical treatment.
In the near future, phosphorus (P) recycling will gain importance in terms of decreasing primary resources. Sewage sludge (SSL) is an adequate secondary P-resource for P-fertilizer production but it is also a sink for heavy metals and organic pollutants. The present study is an investigation on thermochemical P-recycling of SSL. Various temperatures and amendments were tested regarding their performance to remove heavy metals and polycyclic aromatic hydrocarbons (PAH) and simultaneous increase of the plant-availability of P. The investigations were carried out on two types of SSL originating from wastewater treatment plants with chemical P-precipitation and enhanced biological P-removal, respectively. The results show that thermochemical treatment with chlorine donors is suitable to remove the majority of heavy metals and that a combination of a gaseous chlorine donor (HCl) and sodium additives leads to both high heavy metal removal and high plant availability of P. Furthermore, plant experiments Show that almost all investigated thermochemical treatments can significantly reduce the bioavailability and plant uptake of heavy metals. Furthermore, PAHs are secondarily formed during low-temperature treatments (400–500 ° ), but can be significantly reduced by using sodium carbonate as an additive.
Phosphorus (P) for fertilizer use can be recovered from sewage sludge ash (SSA). To enhance the bioavailability of P and reduce the heavy metal content of SSA, it can be treated thermochemically with Na2CO3 or Na2SO4 at 950 °C in a rotary kiln using dry sewage sludge or lignite as reducing agent. These processes were investigated by thermogravimetry/differential thermal analysis coupled with gas analysis. Reducing conditions in this experimental setup were provided by 2 % hydrogen in the Ar carrier gas. During SSA + Na2CO3 treatment CO2, CO and water were detected in the off-gas. During SSA + Na2SO4 treatment SO2, some CO2 and water were detected. Heavy metal removal was more efficient for SSA + Na2CO3 compared to the sulfate variant. A SSA + Na2SO4 + lignite variant which also formed CO shifted the heavy metal removal to the results obtained with Na2CO3 which was obviously due to the additional reduction potential. However, Zn evaporation was not achieved with the Na2SO4 variants which were most probably due to immobilization as ZnS.
Thermal treatment of chromium (III) oxide with carbonates analyzed by far-infrared spectroscopy
(2015)
Chemical state of chromium, sulfur, and iron in sewage sludge ash based phosphorus fertilizers
(2015)
As an essential element of all life forms, phosphorus (P) is vital to the fertilizer industry. With decreasing quantity and quality of phosphate rock resources, recycling P-fertilizers from wastewater is of increasing interest. The P-fertilizer products of a recently developed thermochemical process for P recovery from sewage sludge ash (SSA) were investigated by chromium, sulfur, and iron K-edge X-ray near-edge structure (XANES) spectroscopy. This paper focuses the formation and prevention of toxic chromium(VI) and toxic sulfides during the thermochemical processes. Reducing conditions prevent the oxidation of chromium(III) in the SSA to toxic chromium(VI). Sulfides formed under the reducing conditions are nontoxic iron sulfides. Hematite (Fe2O3) present in the SSA is reduced to magnetite (Fe3O4). A gentle post-treatment at 400 °C under oxidizing conditions converts the iron sulfides into plant-available iron sulfates. This oxidative post-treatment does not form undesired chromium(VI) compounds.
Phosphorus recycling from sewage sludge ash and meat and bone meal by thermochemical treatment
(2009)
Phosphorus can be recycled by thermochemical treatment of sewage sludge ashes using a chlorine-donor at
1000°C. Heavy metals in the sewage sludge ashes are removed and the phosphorus of the developing
phosphate-phases is characterised by a high bioavailability.
The separated heavy metals can be post-treated for recycling purposes. The P-content in the product can be
increased by addition of meat and bone meal into the thermochemical process introducing process energy at the
same time. However, first investigations showed that the elimination rates of heavy metals and the P-solubility in
citric acid decreased if meat and bone meal ash (MBMA) was added to sewage sludge ash before
thermochemical treatment.
A high temperature (1000 °C) thermochemical process for heavy metal removal from sewage sludge ash via the chloride pathway was investigated by thermogravimetry/differential thermal analysis (TG/DTA). TG and DTA measurements gave information about secession and evaporation of water, HCl, and heavy metal chlorides at different temperatures. Additionally, gaseous water and hydrochloric acid which occurred in the process were detected by an FT-IR detector that was coupled to the TG/DTA-system. Heavy metal chlorides which were also formed in the process cannot be detected by this technique. For that reason the outlet gas of the TG/DTA-system was discharged into washing flasks filled with water for absorption. The washing flasks were replaced in temperature steps of 50 °C and the heavy metal concentrations of the solutions were determined by ICP-OES. The temperature-dependent formation/evaporation of different heavy metal chlorides was analyzed and compared for two different thermochemical processes using magnesium chloride hydrate or calcium chloride hydrate as Cl-donors. In both cases evaporation of Cd, Cu, Pb, and Zn was observed from 600 °C, whereas As, Cr, and Ni remained in the solid state. The results were discussed against the background of thermodynamic calculations.
Inorganic phosphorus and nitrogen-phosphorus-potassium (NPK) fertilizers based on phosphates from thermochemically treated sewage sludge ash were analyzed using mid-infrared (mid-IR) and far-infrared (FIR) spectroscopy. The different compounds present in the fertilizers were qualitatively determined with the help of recorded reference spectra of pure substances. Differentiation between various phosphates and other compounds such as sulfates, nitrates, and oxides was possible using combined interpretation of the mid-IR and FIR spectra. The results are in agreement with previous X-ray diffraction (XRD) measurements of the same samples. The main phosphate phases detected were NH4H2PO4, MgHPO4·3H2O, Mg3(PO4)2, Ca5(PO4)5Cl, CaHPO4·2H2O, Ca(H2-PO4)2·H2O, and AlPO4. Furthermore, K2SO4, NH4NO3, Fe2O3, and SiO2 were identified in the IR spectra. However, ammonium and sulfate compounds were only identified in the mid-IR region but were not detectable in the FIR region.
Sewage sludge ash (SSA) is a suitable raw material for fertilizers due to its high phosphorus (P) content. However, heavy metals must be removed before agricultural application and P should be transferred into a bioavailable form. The utilization of gaseous hydrochloric acid for thermochemical heavy metal removal from SSA at approximately 1000 °C was investigated and compared to the utilization of alkaline earth metal chlorides. The heavy metal removal efficiency increased as expected with higher gas concentration, longer retention time and higher temperature. Equivalent heavy metal removal efficiency were achieved with these different Cl-donors under comparable conditions (150 g Cl/kg SSA, 1000 °C). In contrast, the bioavailability of the P-bearing compounds present in the SSA after thermal treatment with gaseous HCl was not as good as the bioavailability of the P-bearing compounds formed by the utilization of magnesium chloride. This disadvantage was overcome by mixing MgCO3 as an Mg-donor to the SSA before thermochemical treatment with the gaseous Cl-donor. A test series under systematic variation of the operational parameters showed that copper removal is more depending on the retention time than the removal of zinc. Zn-removal was declined by a decreasing ratio of the partial pressures of ZnCl2 and water.
Sewage sludge ashes (SSA) contain considerable mass fractions of phosphorus (5-10 w-% P) suitable for fertiliser production. Unfortunately, also most of the heavy metals remain in the ashes. A thermochemical process was developed for the treatment of SSA to i) remove heavy metals and ii) transform phosphates into bio-available mineral phases. The technology was already demonstrated in technical scale (capacity of 300 kg/h) and the company OUTOTEC is currently planning the first industrial plant. In order to manufacture a marketable multi-nutrient fertiliser from the thermochemically treated SSA further wastes and industrial by-products were taken into account. Ammonium sulphate occurs as a by-product of the caprolactam production and was chosen as N-carrier (21 w-% N). Straw ash was tested as potassium carrier (11-15 w-% K). Granulation campaigns were carried out with intensive mixers in lab-, medium-and technical scale. NPS-and NPKS-fertilisers were produced that were characterised by suitable particle size distributions and strength.
Microspectroscopy reveals dust-derived apatite grains in acidic, highly-weathered Hawaiian soils
(2021)
Dust deposition is an important source of phosphorus (P) to many ecosystems. However, there is little evidence of dust-derived P-containing minerals in soils. Here we studied P forms along a well-described climatic Gradient on Hawaii, which is also a dust deposition gradient. Soil mineralogy and soil P forms from six sites along the climatic gradient were analyzed with bulk (X-ray diffraction and P K-edge X-ray absorption near edge structure) and microscale (X-ray fluorescence, P K-edge X-ray absorption near edge structure, and Raman) analysis methods. In the wettest soils, apatite grains ranging from 5 to 30 μm in size were co-located at the micro-scale with quartz, a known continental dust indicator suggesting recent atmospheric deposition. In addition to co-location with quartz, further evidence of dust-derived P included backward trajectory modeling indicating that dust particles could be brought to Hawaii from the major global dust-loading areas in central Asia and northern Africa. Although it is not certain whether the individual observed apatite grains were derived from long-distance transport of dust, or from local dust sources such as volcanic ash or windblown fertilizer, these observations offer direct evidence that P-containing minerals have reached surface layers of highly-weathered grassland soils through atmospheric deposition.
The Brazilian sugarcane industry produced around 173 million tons (Mt) of bagasse in 2018. Bagasse is a by-product of juice extraction for ethanol and sugar production and is combusted in order to generate power, producing up to 10 Mt of ash per year. This ash contains various concentrations of plant nutrients, which allow the ash to be used as a crop fertilizer. However, the concentration and extractability of phosphorus (P), an essential plant nutrient, are low in bagasse ash. To increase the P content, we co-gasified and co-combusted bagasse with P-rich chicken manure. The resulting ash was thermochemically post-treated with alkali additives (Na2SO4 and K2SO4) to increase the availability of P to plants. We aimed to: (i) investigate the effect of thermochemical post-treatment of co-gasification residue and co-combustion ash on P availability to soybeans, (ii) explore the potential of chemical extraction methods (citric acid, neutral ammonium citrate, formic acid, and Mehlich-I) and diffusive gradients in thin films (DGT) to predict the availability of P to soybeans, and (iii) identify the responsible P-phases using X-ray diffraction . We evaluated P availability to soybeans growing in Brazilian Oxisol soil in two independent greenhouse pot experiments. The positive effect of thermochemical treatment on P availability from gasification residue was confirmed through the observation of increased P uptake and biomass in soybean plants. These findings were confirmed by chemical extraction methods and DGT. The gasification residue contained whitlockite as its main P-bearing phase. Thermochemical post-treatment converted whitlockite into highly soluble CaNaPO4. In contrast, co-combustion ash already contained highly soluble Ca(Na,K)PO4 as its main P-bearing phase, making thermochemical post-treatment unnecessary for increasing P availability. In conclusion, increased extractability and availability of P for soybeans were closely connected to the formation of calcium alkali phosphate. Our findings indicate that this combined methodology allows for the prediction of P-fertilization effects of ash.
Phosphorus (P) resource availability is declining and the efficiency of applied nutrients in agricultural soils is becoming increasingly important. This is especially true for P fertilizers from recycled materials, which often have low plant availability. Specific co-fertilization with ammoniumcan enhance P plant availability in soils amended with these P fertilizers, and thus the yield of plants. To investigate this effect, we performed a pot experiment with maize in slightly acidic soil (pH 6.9) with one water-soluble (triple superphosphate [TSP]) and two water-insoluble (sewage sludge-based and hyperphosphate [Hyp]) P fertilizers and anammoniumsulfate nitrate with or without a nitrification inhibitor (NI). The dry matter yield of maize was significantly increased by the NI with the Hyp (from 14.7 to 21.5 g/pot) and TSP (from 40.0 to 45.4 g/pot) treatments. Furthermore, P uptake was slightly increased in all three P treatments with the NI, but not significantly. Olsen-P extraction and P K-edge micro-X-ray absorption near-edge structure (XANES) spectroscopy showed that apatite-P of the water insoluble P fertilizers mobilized during the plant growth period. In addition, novel nitrogen (N) K-edge micro-XANES spectroscopy and the Mogilevkina method showed that the application of an NI increased the fixation of ammonium in detectable hot spots in the soil. Thus, the delay in the nitrification process by the NI and the possible slow-release of temporarily fixed ammoniumin the soil resulted in a high amount of plant available Ammonium in the soil solution. This development probably decreases the rhizosphere pH due to release of H+ by plants during ammoniumuptake, whichmobilizes phosphorus in the amended soil and increases the dry matter yield of maize. This is especially important for water-insoluble apatite-based P fertilizers (conventional and recycled), which tend to have poor plant availability.
Phosphorus (P) fertilizers from secondary resources became increasingly important in the last years. However, these novel P-fertilizers can also contain toxic pollutants such as chromium in its hexavalent state (Cr(VI)). This hazardous form of chromium is therefore regulated with low limit values for agricultural products even though the correct determination of Cr(VI) in these fertilizers may be hampered by redox processes, leading to false results. Thus, we applied the novel diffusive gradients in thin-films (DGT) technique for Cr(VI) in fertilizers and compared the results with the standard wet chemical extraction method (German norm DIN EN 15192) and Cr K-edge X-ray Absorption near-edge structure (XANES) spectroscopy. We determined an overall good correlation between the wet chemical extraction and the DGT method. DGT was very sensitive and for most tested materials selective for the analysis of Cr(VI) in P-fertilizers. However, hardly soluble Cr(VI) compounds cannot be detected with the DGT method since only mobile Cr(VI) is analyzed. Furthermore, Cr K-edge XANES spectroscopy showed that the DGT binding layer also adsorbs small amounts of mobile Cr(III) so that Cr(VI) values are overestimated. Since certain types of the P fertilizers contain mobile Cr(III) or partly immobile Cr(VI), it is necessary to optimize the DGT binding layers to avoid aforementioned over- or underestimation. Furthermore, our investigations showed that the Cr K-edge XANES spectroscopy technique is unsuitable to determine small amounts of Cr(VI) in fertilizers (below approx. 1% of Cr(VI) in relation to total Cr).
Phosphorus (P) resource availability and quality is declining and recycling P-fertilizers from waste materials are becoming increasingly important. One important secondary P resource is sewage sludge (SSL) where P is often bound as aluminum phosphate (Al-P), iron phosphate (Fe-P) and polyphosphate (poly-P), respectively. Thermal treatment in different ways is a promising way in P recycling to produce highly plant-available P-fertilizers. To investigate mechanisms behind transformation of hardly available P-species toward plant-available P forms we treated a model SSL containing different kinds of defined P sources by low-temperature conversion (LTC) at 500 °C and subsequent thermochemical treatment of the LTC product with Na additives (TCT) at 950 °C, respectively. Pot experiments with ryegrass were carried out to determine the plant availability of P of the different treatments. The poly-P (here pyrophosphates) based fertilizers had a very high plant availability after both thermal treatments. During LTC treatment the plant availability of the Fe-P and Al-P variants increased because of the Formation of Fe(II) phosphates and/or pyro-/polyphosphates. Especially the formation of Al-polyphosphate shows a high plant availability. The subsequent TCT further increased strongly the plant availability of the Fe-P variants because of the formation of highly plant-available CaNaPO4. Thus, a direct TCT without prior LTC probably also produce CaNaPO4 and is recommended for Fe-P based SSL. However, a molar Ca/P ratio of 1 in the fertilizer is favorable for CaNaPO4 formation. Thus, the knowledge on the source of primary P in SSL is essential for choosing the accurate thermal treatment method to produce highly plant-available P-fertilizers from SSL.
This paper focuses on the scandium speciation in bauxite residues of different origin. Insights into mineralchemical similarities and differences of these materials will be presented and links to their natural geological background discussed. The presented research should provide fundamental knowledge for the future development of efficient and viable technologies for Sc-recovery from bauxite residues derived from different bauxites and accumulating at different localities. In total, five bauxite residues were investigated which originated from Greece, Germany, Hungary and Russia (North Ural & North Timan) using a combination of different analytical tools. Those included: laser ablation inductively coupled plasma mass spectrometry, X-ray absorption near Edge structure (XANES) spectroscopy, μ-Raman spectroscopy as well as scanning electron microscopy and electron microprobe analyses. X-ray fluorescence and inductively coupled plasma mass spectrometry were used to determine the overall chemical composition. The investigated samples were found to exhibit a relatively homogenous distribution of Sc between the larger mineral particles and the fine-grained matrix except for Al-phases like diaspore, boehmite and gibbsite. These phases were found to be particularly low in Sc. The only sample where Sc mass fractions in Al-phases exceeded 50 mg/kg was the Russian sample from North Ural. Fe-phases such as goethite, hematite and chamosite (for Russian samples) were more enriched in Sc than the Al-phases.
In fact, in Greek samples goethite showed a higher capacity to incorporate or adsorb Sc than hematite. Accessory minerals like zircon, rutile/anatase and ilmenite were found to incorporate higher mass fractions of Sc (>150 mg/kg), however, those minerals are only present in small amounts and do not represent major host phases for Sc. In Russian samples from North Ural an additional Ca–Mg rich phase was found to contain significant mass fractions of Sc (>500 mg/kg). μ-XANES spectroscopy was able to show that Sc in bauxite residue occurs adsorbed onto mineral surfaces as well as incorporated into the crystal lattice of certain Fe-phases. According to our observations the bauxite type, i.e. karstic or lateritic, the atmospheric conditions during bauxitization, i.e. oxidizing or reducing, and consequently the dominant Sc-bearing species in the primary Bauxite influence the occurrence of Sc in bauxite residues. In karstic bauxites, underlying carbonate rocks can work as a pH-barrier and stabilize Sc. This prevents the Sc from being mobilized and removed during bauxitization. Hence, karstic bauxites are more prone to show a Sc enrichment than lateritic bauxites. Reducing conditions during bauxitization support the incorporation of Sc into clay minerals such as chamosite, which can dissolve and reprecipitate during Bayer processing causing Sc to be redistributed and primarily adsorb onto mineral surfaces in the bauxite residue. Oxidizing conditions support the incorporation of Sc into the crystal lattice of Fe-oxides and hydroxides, which are not affected in the Bayer process. The genetic history of the bauxite is therefore the major influential factor for the Sc occurrence in bauxite residues.
Phosphorus (P) is an essential element for all life forms, and P-availability thus an important driver of a functioning agriculture. However, phosphate rock resources for P-fertilizer production are only available in a few countries. Therefore, P-recovery from waste materials has become of increasing interest during the last decade and has been investigated worldwide. In order to characterize potential novel P-fertilizers made from recycled materials, a large array of P-compound characterizations, chemical extractions and growth experiments were performed. This review bundles the work carried out in that field over the last years. Overall, P-fertilizers from recycled materials show a broad range of P-compounds with very different chemical structure and solubility. Growth experiments performed to assess their fertilizing effects display high variations for most of the products. While these experiments have demonstrated that some fertilizers made of recycled materials may reach P effects in the same order of magnitude as water-soluble phosphate rock-based fertilizers, an important limitation in their interpretation is the fact that they often vary considerably in their experimental design. The existing data show clearly that standardization of growth experiments is urgently needed to achieve comparable results. Standard chemical extractants used to assess the chemical solubility of P-fertilizers were found to be of limited reliability for predicting plant P uptake. Therefore, alternative methods such as sequential fractionation, or the extraction of incubated soil/fertilizer mixtures with standard soil extractants or with P sink methods should be tested more intensively in the future to provide alternative options to predict the P-availability of fertilizers from recycled materials.
Uranium and thorium species in phosphate rock and sewage sludge ash based phosphorus fertilizers
(2020)
Phosphorus (P) is an essential element for all forms of life and is thus often applied as phosphate rock-based P-fertilizers in agriculture to enable continuous farming. However, these P-fertilizers contain also hazardous uranium (U) and thorium (Th), up to 660 and 220 mg/kg, respectively. On the contrary, novel P-fertilizers made from sewage sludge (ash) contain only low mass fractions of U and Th. In addition to the total amount of U and Th in P-fertilizers, their mobility and bioavailability is important, which depends to a large extent on their chemical state, especially oxidation state and chemical bonding. Thus, we analyzed their chemical state in various P-fertilizers by U and Th L3-edge HERFD-XANES spectroscopy. Phosphate rocks and sewage sludge-based P-fertilizers contain mainly U(IV) compounds which have only a low bioavailability. In contrast, acidic treatment of phosphate rock to produce super phosphates lead to an oxidation to U(VI) compounds (including formation of uranium phosphates) with a strongly increased bioavailability. On the contrary, all analyzed P-fertilizers contain Th in form of strongly insoluble phosphates and oxides with a low bioavailability. Additionally performed water extractions and Diffusive Gradients in Thin-films (DGT) experiments support these findings.
A wide range of methods are used to estimate the plant-availability of soil phosphorus (P). Published research has shown that the diffusive gradients in thin films (DGT) technique has a superior correlation to plant-available P in soils compared to standard chemical extraction tests. In order to identify the plantavailable soil P species, we combined DGT with infrared and P K- and L2,3-edge X-ray adsorption near edge structure (XANES) spectroscopy. This was achieved by spectroscopically investigating the dried binding layer of DGT devices after soil deployment. All three spectroscopic methods were able to distinguish between different kinds of phosphates (poly-, trimeta-, pyro- and orthophosphate) on the DGT binding layer. However, infrared spectroscopy was most sensitive to distinguish between different types of adsorbed inorganic and organic phosphates. Furthermore, intermediates of the time-resolved hydrolysis of trimetaphosphate in soil could be analyzed.
The present study shows the potential of high-resolution imaging and nano-Fourier-transform infrared (nano-FTIR) spectroscopy for corrosion science. The protective oxidation layers of different chlorine-gas treated silicon
carbides (SiCs) were characterized with these techniques. A nitrified SiC showed the highest resistant strength against chlorine corrosion at 1000 °C compared to the other SiCs. Nano-FTIR spectroscopy with a lateral resolution below 40 nm detected differences in the crystallinity of the bulk-SiC and in the transitional region to the protective layer. Furthermore, high-resolution imaging provides deep insight in the interfacial layer between bulk-SiC and the protective oxidation layer on sub-micrometer scale.
Sewage sludge and sewage sludge ashes (SSA) are produced in huge amounts at municipal waste water treatment plants (WWTP) all around the world and have become an issue for many urbanized areas. To deal with this unceasing mass flow in an ecologically and economically responsible way a comprehensive chemical and structural characterization of all types of SSA is needed. X-ray powder diffraction (XRD) is one of the most promising analytical methods for this task. Although, there has been ample chemical evidence showing that many SSA contain aluminium phosphate as a major component up to now no aluminium phosphate or aluminium-rich mixed phosphate phase has been reported to be identified by XRD in a SSA produced at a mono-incineration facility. The outcome of the present com-bined XRD and Mossbauer spectroscopy investigation provides comprehensive evidence closing this gap for the first time.
Enhanced post-denitrification without addition of an external carbon source in membrane bioreactors
(2005)
This study investigates a post-denitrification process without the addition of an external carbon source combined with an enhanced biological phosphorus removal (EBPR) in a membrane bioreactor (MBR). Three trial plants, with two different process configurations, were operated on two different sites, and a variety of accompanying batch tests were conducted. It was shown that even without dosing of an external carbon source, denitrification rates (DNR) much above endogenous rates could be obtained in post-denitrification systems. Furthermore, the anaerobic reactor located ahead of the process had a positive impact on the DNR. Given these surprising results, the project team decided to identify the carbon source used by the microorganisms in the post-denitrification process. Batch tests could demonstrate that lysis products do not play a major role as a C-source for post-denitrification. The following hypothesis was proposed to explain the observations: the glycogen, internally stored by the substrate accumulating bacteria, if anaerobic conditions are followed by aerobic conditions could act as carbon source for denitrification in post-denitrification system. First exploratory batch tests, where the glycogen evolution was monitored, corroborate this assumption.
Sewage sludge ashes (SSA) represent a possible source of phosphorus (P) and technology metals. So far, the sole external source for P, that is indispensable for all animate beings, is rock phosphate, a finite resource. The EU depends completely on the import from possible politically instable regions. Furthermore, rock phosphate is often contaminated with heavy metals like Cd and U, leading to health and environmental hazards. P recovered from SSA might diminish these problems. SSA of German mono incineration facilities are analyzed for their elemental composition. More than 95% of the emerging SSA is monitored, enabling the determination of complete mass flows of the ashes and their components. Initial results indicate a P recovery potential of 16,000 t/a (11% of the annual P demands for fertilizer production). The concentrations of Cd and U in SSA are one to two Orders of magnitude lower than in rock phosphate and could help to reduce possible hazards.
Fused cement clinker can be produced from molten basic oxygen furnace slag (BOFS) by way of a reductive thermochemical treatment. During the thermochemical treatment, oxidic iron is reduced to metallic iron and separated. The resulting low-iron slag has a chemical and mineralogical composition similar to ordinary Portland cement (OPC) clinker. In this study, the hydraulic reactivity of the fused clinker from BOFS with and without gypsum was investigated using isothermal calorimetry, differential scanning calorimetry, in situ X-ray diffraction and powder X-ray diffraction. Furthermore, a synthetic fused clinker without foreign ions and fused clinker produced by a mixture of both materials was studied. The hydraulic reaction of the fused clinker from BOFS was considerably slower than that of OPC. However, the reaction can be accelerated by adding gypsum as a sulfate carrier. Furthermore, the results showed an increased reaction rate with decreasing content of foreign ions such as Fe, P or Mn.
Wastewater contains a diverse array of organic and inorganic compounds and its complex composition strongly depends on the location and the connected dischargers. However, municipal wastewater as a carrier of feces and urine generally contains considerable amounts of the main nutrients nitrogen and phosphorus. The latter is in the focus of the discussions about the recovery potential of wastewater due to the relatively high mass flows of phosphorus in wastewater and the finite nature and decreasing quality of phosphate rock reserves. But due to the presence of the whole periodic table of elements, wastewater might contain further valuable components of interest for recovery including those defined as critical raw materials by the European Commission. Phosphorus and most of the other critical raw materials are fixed in the sewage sludge and after incineration in the sewage sludge ash (SSA). This is accompanied by high concentration factors from wastewater via sludge to ash. However, the mass fractions of the majority of elements in sewage sludge are comparable to those of the earth crust, indicating no relative enrichment. Nevertheless, enrichment factors of 100 or higher are given for phosphorus, copper, zinc, cadmium, silver, tin, lead and the platinum group elements indicating an anthropogenic input. An economic value of sewage sludge was estimated to $460,-/t calculated on the basis of the respective market prices for high purity elements – a theoretical value. A German survey of sewage sludge ashes showed that the mass fractions and the mass flows of most of the elements present in SSA are probably too low for an economic recovery. In most cases the mass flows are rather small compared to the imports and the chemical forms are not suitable for recovery. An exception is phosphorus that is present in high mass fractions up to 13% and that bears a high substitution potential. If the application of P-recovery technologies lead to a further concentration of valuable elements e.g. as by-products in side streams of the process, it would probably make also the recovery of other elements of economic interest.
This paper presents an inventory of sewage sludge ashes (SSA) generated in the mono-incineration plants for municipal sewage sludge in Poland. This research focused on the detailed study of mass flows, chemical composition, and phosphorus recovery potential. There are currently 11 sludge mono-incineration plants operated with a total capacity of 160,300 Mg dry weight (d.w.) of sludge annually. Recently, a significant increase in the amount of SSA generated in these plants has been observed, reaching 26,756 Mg in 2018. Chemical composition of SSA showed significant amounts of the main nutrients: calcium (~14%), phosphorus (~13%), magnesium (~3%), and potassium (~1%). Additional main elements were iron (~14.5%), silicon (~13%), and aluminium (~6%). The main trace elements in the SSA were zinc (~3750 mg/kg) and copper (~899 mg/kg). Pollutants, according to fertilizer regulations of different countries, present in Polish SSA were chromium(~703 mg/kg), nickel (~260 mg/kg), lead (~94 mg/kg), and Cadmium (~9 mg/kg). The radionuclides, uranium, and thorium often present in higher amounts in commercial phosphate rock-based fertilizers, were only detected in SSA t low levels of 4–9 mg/kg and 2–3 mg/kg, respectively. Theoretical phosphorus recovery potential from the SSA (from plants in Cracow, Lodz, Gdansk, Gdynia, Szczecin, and Kielce) was estimated at 1613.8 Mg, of which 33.9% is bioavailable. Currently, in Poland, the recommended approach is the production of fertilizers as a result of the extraction of phosphorus from the SSA with its use in the production of secondary mineral fertilizers.
Further research in this area is required considering Polish conditions and legislation.
One of the typical wastes produced in blast-furnace (BF) ironmaking is BF sludge, which mostly consists of carbon and iron oxides, but also contains toxic trace metals such as Zn, Pb, Cd, As, and Hg that render the material hazardous. Due to the lack of an established recycling process, BF sludges are landfilled, which is ecologically questionable and costly. Here, we investigate selective removal of Zn, Pb, and Cd from BF sludge by chlorination–evaporation reactions using thermodynamic modelling and laboratory-scale experiments. Specifically, BF sludge was thermochemically treated at 650–1000 °C with a spent iron(II) chloride solution from steel pickling and the effects of process temperature and retention time on removal of Zn, Pb, and Cd were investigated. Zinc and Pb were quantitatively removed from BF sludge thermochemically treated at 900–1000 °C, whereas Fe and C as well as other major elements were mostly retained. The Zn, Pb, and Cd contents in the thermochemically treated BF sludge could be lowered from ∼56 g/kg, ∼4 g/kg, and ∼0.02 g/kg to ≤0.7 g/kg, ≤0.02 g/kg, and ≤0.008 g/kg, respectively, thus rendering the processed mineral residue a non-hazardous raw material that may be re-utilized in the blast furnace or on the sinter band.
The very strong Lewis acid aluminium chlorofluo-ride (ACF) was loaded with anhydrous HF. The interactionbetween the surface of the catalyst and HF was investigatedusing a variety of characterization methods, which revealed he formation of polyfluorides. Moreover, the reactivity ofthe HF-loaded ACF towards the hydrofluorination of alkyneswas studied.
Fluorescence lamps contain considerable amounts of rare earth elements (REE). Several recycling procedures for REE recovery from spent lamps have been established. However, despite their economic importance, the respective recycling is scarce so far, with an REE recovery rate of less than 1%. A reliable analysis of REE and other relevant metals like Yttrium is crucial for a thorough and complete recovery process. This applies both to the solid matter and aqueous phase, since most of the recycling processes include wet-chemical steps. We tested seven different reagent mixtures for microwave-assisted digestion of fluorescent lamp shredder, including hydrofluoric acid, perchloric acid, and hydrogen peroxide. We determined the concentrations of 25 of the most relevant rare earth and other trace elements (Al, P, Ti, V, Cr, Fe, Ni, Cu, Ga, Ge, As, Y, Ag, Cd, Sn, Sb, La, Ce, Eu, Gd, Tb, W, Au, Hg, and Pb) in the respective dilutions. Two independent digestions, one a mixture of perchlorid/nitric/hydrofluoric acid and the other aqua regia, showed the highest concentrations of 23 of these elements, excluding only Sn and Tb. The REE concentrations in the tested lamp shredder sample (stated in g/kg) were 10.2 (Y), 12.1 (La), 7.77 (Ce), 6.91 (Eu), 1.90 (Gd), and 4.11 (Tb).
Complete survey of German sewage sludge ashes - phosphorous and technology metal recovery potential
(2014)
Sewage sludge ashes (SSA) are a possible source for recovery of phosphorous (P) and technology metals. Phosphorous is essential for all animate beings. So far, its sole external source is rock phosphate, which is a finite resource. The EU import dependency on P from regions with high domestic demands or political instabilities is almost complete. Furthermore, rock phosphate often contains high amounts of heavy metals like Cd and U that might lead to health and environmetal hazards. P recovered from SSA might diminish these problems. We analyzed SSA from German mono incineration facilities in terms of their elemental composition and respective recovery potential. More than 97% of the emerging SSA is monitored, enabling the determination of complete mass flows of the ashes and their components. Results indicate a P recovery potential of 19,000 t/a (more than 12% of the annual P demands for fertilizer production). The concentrations of Cd and U in SSA are significantly lower than in rock phosphate and thus might help to reduce possible envrionmental and health hazards.
Due to the great quantities of construction and demolition waste in Europe, the reuse of building material waste as secondary raw materials is of particular importance. A recycling of building materials can meet the requirements of sustainability in several aspects: the extended time availability of primary raw materials and the related protection of natural resources as well as the saving of landfill sites. In recent years sulphates originating from gypsum in secondary building materials, made of construction and demolition waste, received growing attention. Sulphates are unwanted in secondary building materials for concrete production as well as for other use e.g. in unbounded layers. The content of gypsum resp. sulphates in secondary aggregates can be reduced by different methods. Depending on the type of material different steps for selective dismantling can be used to separate gypsum containing residues from concrete rubble. Furthermore some steps for the processing of building rubble are suitable for the reduction of sulphates in the produced aggregates. An environmental evaluation of different ways for the production of recycled concrete aggregates was performed with regard to a reduction of sulphates in the secondary building material. The use of techniques for selective dismantling was environmentally advantegous for the deconstruction of three investigated model houses.
More sustainable waste management practices are an important element in the Transformation towards a circular economy (CE). Activities in this area should be dedicated to all groups of waste, including those generated in the water and sewage sector. This paper presents the characteristics of sewage sludge ash (SSA) coming from Polish municipal waste incineration plants. Due to the high content of nutrients such as phosphorus (8.01% P2O5), calcium (5.11% CaO) and magnesium (2.75% MgO), the analyzed SSA may constitute a valuable source of raw materials for the fertilizer industry.
Despite the good fertilizing properties of the SSA, in some cases the presence of heavy metals such as cadmium (0.74–1.4 mg/kg dry matter), lead (49.8–99 mg/kg dry matter), mercury (3.93 mg/kg dry matter) and arsenic (4.23–4.43 mg/kg dry matter) and poor bioavailability of P from SSA disqualifies this waste from direct use as a fertilizer. Therefore, it is necessary to look for methods that will allow the municipal SSA to be processed, for example, technologies for the extraction of phosphorus and the production of phosphate fertilizer. This way of SSA management is in the line with the CE assumptions, in which waste becomes a valuable source of secondary raw materials. Fertilizer produced from waste meeting quality, safety and labelling requirements and limits of organic, microbiological and physical contaminants will be able to be traded freely within the European Union (EU) and receive the CE marking. The idea of use of SSA for fertilizer purposes is consistent not only with the objectives of the CE but also with the Polish National Waste Management Plan 2022 and the Municipal Sewage Sludge Strategy 2019–2022, which emphasizes the necessity to maximize the use of biogenic substances contained in wastewater. Therefore, sustainable management of SSA, in particular its storage in a way enabling the recovery of phosphorus, should be promoted.
Conventional fertilisers have their disadvantages as nutrient release is not synchronised with the demand of plants. Several approaches of "next generation fertilisers" are aiming at controlled nutrient release. Recycling fertilisers are often not soluble in water but fully plant available. They are suitable raw materials for the production of new types of controlled release fertilisers.
The annual demand of phosphorus (P) for fertilizer use is more than 550,000 t in Germany. Several of the input streams like mineral fertilizer produced from phosphate rock or sewage sludge are problematic due to contamination with heavy metals and organic pollutants and/or supply risks. Phosphorus recovery from the wastewater stream might help to diminish these problems. Several procedures have been developed to recover P from either sewage sludge ash (SSA) or wastewater via precipitation or crystallization as struvite. This study determined the elemental composition and trace metal mass fractions of 252 SSA samples and 17 struvite samples from wastewater treatment plants (WWTP) to see whether there are differences related to the source of the sludge (municipal/industrial) or the stage of the WWTP where the struvite is produced. Results indicated that there is no clear trend of the elemental mass fractions related to the source of the sludge. All struvite samples show very low heavy metal contents, even though the struvite precipitated from the sludge shows slightly elevated heavy metal mass fractions compared to struvite crystallized from sludge liquor. Struvite is a clean and plant available material for fertilizer production from wastewater streams and has some advantages for the wastewater treatment plant. However, since the P recovery rate of struvite processes is low (7–11%) compared to that from SSA processes (90%), recovery from SSA is necessary for a substantial P recovery from the wastewater stream.
There is a growing concern of the direct use of contaminated sewage sludge in agriculture due possible environmental and health hazards. Thus, incineration of the sludge and thus increasing amounts of sewage sludge ashes (SSA) are to be expected in the future. SSA contains considerable amounts of phosphorus (P) and technology metals that might be recovered as secondary raw materials. Since the EU for instance depends completely on the import of rock phosphate needed for fertilizer production, alternative sources for P are in order. Furthermore, rock phosphate is often contaminated with heavy metals like Cd and U, leading to health and environmental hazards. P recovered from SSA might diminish these problems. To determine the possible recovery potential of P and technology metals from SSA, we conducted a survey of German mono incineration facilities and analyzed the respective SSA for their elemental composition. More than 95% of the emerging SSA was monitored. Results indicate a P recovery potential of 18,000 t/a (up to 13% of the annual P demands for fertilizer production). The concentrations of Cd and U in SSA are one to two Orders of magnitude lower than in rock phosphate and could help to reduce possible hazards.
Recovery of rare earth elements - optimized elemental analysis of fluorescent lamp shredder waste
(2016)
Rare earth elements (REE) are a crucial component of fluorescence lamps. Several procedures have been developed to recovery these technological important elements. Nevertheless, actual REE recycling from fluorescence lamps is scarce so far (recovery rate of less than 1 %), with current recycling approaches concentrating on glass recovery. Since most recycling processes include several, also wet-chemical steps, a complete knowledge of the actual elemental composition of the respective mass flows is necessary for an efficient REE recovery. We tested seven different reagent mixtures for microwave-assisted digestion of fluorescent lamp shredder, including HF, HClO4, and H2O2. We determined the concentrations of 25 of the most relevant rare earth and other trace elements in the respective dilutions. Two independent digestions, one a mixture of perchlorid/nitric/hydrofluoric acid and the other aqua regia, showed the highest concentrations of 23 of these elements, excluding only Sn and Tb. The REE concentrations in the tested lamp shredder sample (stated in g/kg) were 10.2 (Y), 12.1 (La), 7.77 (Ce), 6.91 (Eu), 1.90 (Gd), and 4.11 (Tb).
Concrete is one of the most widely used construction materials and, accordingly, the concrete industry is an important stakeholder in the field of sustainable construction. Therefore various approaches have been implemented to increase the sustainability of concrete. Besides reducing CO2-emissions during cement production, increasing the energy efficiency of buildings and extending their life span, the end-of-life performance of concrete is also an essential aspect of sustainability. Reusing concrete as a secondary building material meets the requirements of sustainability in several ways: the extended time availability of primary raw materials and, thereby, the protection of natural resources as well as conserving landfill site. Furthermore, the production of recycled concrete aggregates (RCA) is a good example for closed-loop recycling.
However, regarding the use of RCA as a substitute for natural aggregates in concrete, attention must be paid to all issues of sustainability: this means that environmental, economic and social aspects have to be considered. Since RCA generally have inferior building material properties, such as higher porosity and lower density, the implementation of closed-loop recycling of concrete only makes sense if the technical quality assurance is secured. This paper focusses on the implementation of techniques for the deconstruction/demolition of buildings and the subsequent treatment of concrete rubble in order to improve the building material properties of RCA with regard to the requirements of sustainability and also technical rules and standards.
Concrete is one of the most widely used construction materials and, accordingly, the concrete industry is an important stakeholder in the field of sustainable construction. Therefore various approaches have been implemented to increase the sustainability of concrete. Besides reducing CO2-emissions during cement production, increasing the energy efficiency of buildings and extending their life span, the end-of-life performance of concrete is also an essential aspect of sustainability. Reusing concrete as a secondary building material meets the requirements of sustainability in several ways: the extended time availability of primary raw materials and, thereby, the protection of natural resources as well as conserving landfill site. Furthermore, the production of recycled concrete aggregates (RCA) is a good example for closed-loop recycling.
However, regarding the use of RCA as a substitute for natural aggregates in concrete, attention must be paid to all issues of sustainability: this means that environmental, economic and social aspects have to be considered. Since RCA generally have inferior building material properties, such as higher porosity and lower density, the implementation of closed-loop recycling of concrete only makes sense if the technical quality assurance is secured. This paper focusses on the implementation of techniques for the deconstruction/demolition of buildings and the subsequent treatment of concrete rubble in order to improve the building material properties of RCA with regard to the requirements of sustainability and also technical rules and standards.
Due to the large quantities of construction and demolition waste (CDW) in Europe, its reuse or recycling is of particular importance. Although several countries already recycle high amounts of CDW, the use as secondary raw materials is often limited by inferior building material properties. Specific characteristics, like high porosity and low density are caused by hardened cement paste in crushed concrete and the content of mortar and plaster in brick debris. Impurities like wood or gypsum and also harmful substances like organic pollutants may be a major problem for a reuse and should be minimized. Therefore unwanted materials and impairing substances have to be separated from the secondary building material stream. This can be done during the demolition process by using techniques for selective dismantling or during the subsequent treatment of the resulting rubble. Since almost all processing steps are associated with environmental impacts, the benefits of saving natural resources by applying secondary building materials should be weighed carefully. An environmental performance evaluation was undertaken to assess different techniques for reducing gypsum in recycled concrete aggregates, aiming at a minimization of elutable sulfates. These results were compared to the environmental impacts of the extraction of natural aggregates for concrete.
Stocks of high grade phosphate rock are becoming scarce, and there is growing concern about potentially harmful impurities in conventional phosphorus fertilizers. Sewage sludge ash is a promising secondary phosphorus source. However, to remove heavy metals and convert the phosphorus contained in sewage sludge ash into mineral phases available to plants, an after-treatment is required. Laboratory-scale calcination experiments of sewage sludge ash blended with sodium salts using dried sewage sludge as a reducing agent were carried out at 1000 °C. Thus, the Ca3(PO4)2 or whitlockite component of raw sewage sludge ash, which is not readily plant available, was converted to CaNaPO4 (buchwaldite). Consequently, nearly complete phosphorus solubility in ammonium citrate (a well-established indicator for plant availability) was achieved. Moreover, it was shown that Na2CO3 may be replaced by moderately priced Na2SO4. However, molar ratios of Na/P > 2 were required to achieve >80% phosphorus solubility. Such over-stoichiometric Na consumption is largely caused by side reactions with the SiO2 component of the sewage sludge ash – an explanation for which clear evidence is provided for the first time.
This study focuses on the question whether heat treated sewage sludge ashes are more favourable as fertilizers than untreated sewage sludge ashes (USSA) and whether their fertilization effects are comparable with commercial triple superphosphate (TSP). In a pot experiment, maize was fertilized either with one of three heat treated and Na-, Ca- and Si-compounds amended sewage sludge ashes (two glown phosphates, steel mill slag + sewage sludge ash) or USSA or TSP as control. Fertilization with USSA did not increase the biomass yield and the P uptake of maize in comparison to the P0 treatment (7.25 resp. 8.35 g dry matter/pot). Fertilization with heat treated sewage sludge ashes and TSP resulted in significantly higher yields and plant P uptakes which are on average eight times higher than treatment with USSA and P0 control. Biomass yields and P uptake of maize after fertilization with heat treated sewage sludge ashes are not significantly different from those after TSP fertilization. The main P compound in USSA is Ca3(PO4)2. By heat treatment and amendment with different sodium, calcium, sulphur and silicon containing additives or steel mill converter slag, Ca3(PO4)2 is converted to Ca- and Na-silico-phosphates, which have a higher water solubility than Ca3(PO4)2. This increased solubility is responsible for the high plant availability of this phosphates.
Phosphorous is essential for all living creatures and indispensable in its functions regarding bone structure, energy metabolism, and storage and expression of genetic information. It is removed from the soils through farming and husbandry and has to be replaced. Annually, more than 17 million tons of phosphorous are applied to soils in the form of mineral fertilizer worldwide (Killiches, 2013). In Germany, this accounts for 150,000 t/a. This fertilizer is produced from rock phosphate, which is often contaminated with heavy metals (Dissanayake et al., 2009), especially cadmium and uranium. Cd concentrations are around 30 mg/kg, U around 100 mg/kg, with even higher peak values. Since rock phosphate is treated with acids to make the phosphorous bioavailable, those heavy metals were also mobilized. When the fertilizer is applied to the farmland, the contaminants can pollute the soil and pose an environmental risk. Sewage sludge is another phosphorous source for farming. In Germany, 15,000 t/a phosphorous are applied to farmlands this way. However, there is a growing concern of possible environmental hazards since sewage sludge contains not only inorganic contaminants but also organic pollutants, especially pharmaceuticals and personal care products (Guardia et al., 2004).
Incineration of sewage sludge is expected to increase in the future due to growing concerns about the direct use of sludge in agriculture. Sewage sludge is the pollutant sink of wastewater treatment and thus loaded with contaminants that might pose environmental hazards. Incineration degrades organic pollutants efficiently, but since the ash is currently mostly disposed of, all valuable component like phosphorus (P) and technologically relevant metals present in the sewage sludge ash (SSA) are removed from the economic cycle entirely. We conducted a complete survey of SSA from German mono-incineration facilities and determined the theoretical recovery potential of 57 elements. German SSA contains up to 19,000 t/a P which equals approximately 13% of phosphorus applied in the German agriculture in form of phosphate rock based mineral fertilizers. Thus, SSA is an important secondary resource of P. However, its P-solubility in ammonium citrate solution, an indicator for the bioavailability, is only about 26%. Treatment of SSA is recommended to enhance P bioavailability and remove heavy metals before it is applied as fertilizer. The recovery potential for technologically relevant metals is generally low, but some of these elements might be recovered efficiently in the course of P recovery exploiting synergies.
The number of different secondary raw materials used for fertilizer production is expected to increase in the future due to newly developed recycling procedures. Thus, more and more different matrices have to be analyzed. Furthermore, the respective legislation and analytical methodology is nonuniform throughout Europe. Therefore, a harmonization of the the regulations and Standards is desirable. We conduct a research project to test the existing analytical methods on their applicability to a broad variety of matrices to support the harmonization process. The project is scheduled tili late spring 2017. Initial results will be presented.
The amount of sewage sludge produced worldwide is expected to further increase due to rising efforts in wastewater treatment. There is a growing concern against its direct use as fertilizer due to contamination of the sludge with heavy metals and organic pollutants. Incinerating the sludge degrades organic compounds almost completely and concentrates heavy metals and phosphorus. However, the sewage sludge ash (SSA) is almost completely disposed of and with it all resources are removed from the economic cycle. Comprehensive knowledge of the composition of SSA is crucial to assess the resource recovery potentials. We conducted a survey of all SSA emerging in Germany and determined the respective mass fractions of 57 elements over a period of one year. The median content of phosphorus was 7.9%, indicating an important recovery potential. Important trace elements were Zn (2.5 g/kg), Mn (1.3 g/kg), and Cu (0.9 g/kg). Mass fractions of technology metals such as V, Cr, Ga, Nb, and rare earths were comparatively low. Considering the possible use of SSA as secondary raw material for fertilizer production it should be noted that its Cd and U content (2.7 mg/kg and 4.9 mg/kg respectively) is significantly lower than that of rock phosphate based mineral fertilizers.
This study compares the mercury distribution in the vapor phase, the phosphor powder and the glass matrix of new and spent fluorescent lamps. The spent fluorescent lamps were obtained at the collection yards of a public waste management company in Hamburg, Germany. An innovative systematic sampling method is utilized to collect six spent and eight corresponding new, off-the-shelf fluorescent lamp samples. The efficiency of several acid digestion methods for the determination of the elemental composition was studied and elemental mass fractions of K, Na, Y, Ca, Ba, Eu, Al, Pb, Mg, Hg, and P were measured. The study also finds aqua regia to be the best reagent for acid digestion. However, no significant difference in mercury distribution was found in the different phases of the new and spent fluorescent lamps.
The SUSAN-project aimed at developing a sustainable and safe strategy for nutrient recovery from sewage sludges using thermal treatment. Mono-incineration of the sludges completely destructs the organic pollutants in a first step. The incineration residues are ashes with a high phosphorus content that still contain heavy metal compounds above the limits for agricultural use. Furthermore, phosphorus in the ashes exhibits low bioavailability - a disadvantage in farming. Therefore, in a second thermochemical step heavy metals are removed and phosphorus transferred into mineral phases available for plants. The principle of the SUSAN-project is the separation of the small heavy metals fraction from the ashes to receive a phosphorus rich product suited as raw material for fertilisers that also contains SiO2, CaO, Al2O3, Fe2O3, MgO and K2O.
The thermochemical process is based on evaporation of volatile heavy metal chlorides at 850 - 1000 °C. The sewage sludge ashes are mixed with chlorine donors such as MgCl2 or KCl, grained and treated in a thermal aggregate e.g. a rotary furnace. At the same time a transfer of non soluble P-compounds into Mineral phases available for plants takes place.
Besides technological development of the thermochemical process, the products fertilisation performance, the product design, the market for the products and the sustainability of the whole process chain are emphasised in the SUSAN-project.
The rare earth elements (REEs) are a group of 17 elements from the lanthanide series including scandium and yttrium that share similar physical and chemical properties. They are progressively important for transition to a green, low-carbon economy due to their vital role in electric cars, permanent magnets, fluorescent lamps, rechargeable NiMH batteries, catalysts and other applications. In reality, the term “rare” is misleading as these elements are widely present in the earth’s crust. However, even if not rare, REEs have a high supply risk due to the geopolitical situation e.g. resulting from limited Chinese exports. This, along with their importance in various clean and high-tech applications, has led the EU and the U.S. to label certain REEs, especially europium, terbium and yttrium as critical elements. Recycling is often considered as one of the ways to reduce REEs criticality, especially the import dependency.
A recycling strategy for REE requires reliable analytical data of different types of waste streams. The REE bearing waste matrices can be completely different depending on its origin. Digestion methods prior to ICP-OES / -MS analysis must be optimized for the different matrices to guarantee reliable results. We present two examples of different REE bearing waste streams - fluorescence lamp shredder waste and red mud - and show how the analytical procedures were optimized.
The importance of secondary raw materials for phosphorus (P) fertilizer production is expected to increase in the future due to resource depletion, supply risks, and heavy metal contamination of fossil phosphate resources. Municipal wastewater is a promising source for P recovery. In Germany for instance, it contains almost 50% of the total amount of P that is currently applied as mineral fertilizer. Several procedures have been developed to recover and re-use P resulting in a growing number of recycling fertilizers that are currently not regulated in terms of fertilizer efficiency. We tested various materials and matrices for their total P content, solubility of P in neutral ammonium citrate (Pnac) and water, and performed robustness tests to check if existing analytical methods are suitable for those new materials. Digestion with inverse aqua regia was best suited to determine the total P content. Pnac sample preparation and analyses were feasible for all matrices. However, we found significant time and temperature dependencies, especially for materials containing organic matter. Furthermore, several materials didn’t reach equilibrium during the extractions. Thus, strict compliance of the test conditions is strongly recommended to achieve comparable results.
Phosphorus (P) is essential for all forms of life and cannot be substituted. It is one of the macro nutrients applied in form of mineral or organic fertilizers in agricultural crop production. Mineral P fertilizers are generally based on phosphate rock, a limited resource. Western Europe completely depends on imports as it has no own relevant phosphate mines. The most abundant phosphate deposits are located only in a few countries such as Morocco, China, South Africa and the United States of America. Furthermore, phosphate rock and as a consequence mineral P fertilizers are often contaminated with the toxic elements cadmium and uranium. In Order to substitute phosphate rock P-bearing waste streams are investigated for their potential to be recyded as fertilizers. Wastewater is one of the important P-bearing waste streams that were in the focus of research in the last 10 years. German wastewater is e.g. a carrier of approx. 70,000 t of phosphorus per year.
Calcium alkali phosphates Ca(Na,K)PO4 are main constituents of bioceramics and thermochemically produced phosphorus fertilizers because of their bioavailability. Sparse thermodynamic data are available for the endmembers CaNaPO4 and CaKPO4. In this work, the missing data were determined for the low-temperature phase modifications of the endmembers CaNaPO4 and CaKPO4 and three intermediate Ca(Na,K)PO4 compositions. Standard enthalpy of formation ranges from - 2018.3 ± 2.2 kJ mol-1 to - 2030.5 ± 2.1 kJ mol-1 and standard entropy from 137.2 ± 1.0 J mol-1 K-1 to 148.6 ± 1.0 J mol-1 K-1 from sodium endmember b-CaNaPO4 to potassium endmember b0-CaKPO4.
Thermodynamic functions are calculated up to 1400 K for endmembers and the sodium-rich intermediate phase b-Ca(Na0.93K0.07)PO4. Functions above 640 K are extrapolated because of the phase transition from low- to high-temperature phase. Impurities in the synthesized intermediate phases c-Ca(Na0.4K0.6)PO4 and c-Ca Na0.35K0.65)PO4 and one additional phase transition around 500 K impeded the determination of high-temperature thermodynamic functions. In general, data for phase transition temperatures agree with the previously reported phase diagrams.
Sewage sludge ashes (SSA) contain up to 13% P and are thus promising raw materials for fertilizer production. However, SSAs also contain heavy metals and the main P-bearing mineral phases whitlockite and aluminium phosphate are poorly bioavailable. We developed and patented a process that produces fertilizers from SSA addressing the above mentioned challenges. SSA is thermo-chemically treated at ~950°C under reducing conditions (reductive: dry sewage sludge) in a rotary kiln together with an alkali compound such as sodium or potassium sulfate, hydroxide or carbonate. Some undesired trace elements such as As, Hg, Pb and Cd are evaporated and separated via off gas treatment system. The poorly soluble phosphates are transformed into calcium alkali phosphates (CaNaPO4 or CaKPO4) that are not water soluble but completely soluble in neutral ammonium citrate solution (NAC). Pot experiments showed that the fertilizer performance of the treated SSA containing calcium alkali phosphates as the single P-bearing mineral phase was comparable to the performance of triple superphosphate. The PNAC-solubility of fertilizer products correlated very well with the resulting contents of calcium alkali phosphates and the P-uptake of plants in pot experiments. The effect of the ratio alkali/P on the PNAC-solubility was investigated by crucible experiments and trial series with a medium scale rotary kiln using different SSAs and alkali phosphates. The effects of operational parameters such as the temperature and the retention time were investigated as well as concurring side reactions of the alkali compounds e.g. with SiO2 present in SSA. The alkali/P ratio must be roughly adjusted at 2 to achieve 100% PNAC-solubility for a common type of SSA. A demonstration trial with an output of 2 t recycling fertilizer was carried out in an industrial rotary kiln (product output 30 kg/h). The PNAC-solubility of the product varied between 60% and 80% during the 4 days campaign showing that the transformation of the mineral P-phases to calcium alkali phosphates was not complete. This was observed although the amount of Na2SO4 additive was dosed according to the results of the pre-investigations. Structure analysis by XRD showed that besides the target compound CaNaSO4 also some Ca3(PO4)2 remained in the SSA as well as some unreacted Na2SO4 additive. Obviously, the conditions in the industrial rotary kiln were not optimal for the process showing that some process aspects have to be reconsidered for the scale-up.
An environmentally friendly and cost efficient way for the management of municipal solid waste incineration (MSWI) fly ash represents its thermal co-treatment together with combustible waste. However, the safe introduction and storage of MSWI fly ash in the waste bunker is challenging and associated with severe problems (e.g. dust emissions, generation of undefined lumps and heat in case of moistened MSWI fly ash). Therefore, the aim of this study is to investigate the suitability of pelletisation as a pretreatment of MSWI fly ash. In particular, MSWI fly ash was characterised after sampling, pelletisation and thermal treatment and the transfer of constituents to secondary fly ash and flue gas was investigated. For this purpose, MSWI fly ash pellets with a water content of about 0.15 kg/kg and a diameter of about 8 mm have been produced by disc pelletiser and treated in an electrically heated pilot-scale rotary kiln at different temperatures, ranging from 450°C to 1050°C. The total contents of selected elements in the MSWI fly ash before and after thermal treatment and in the generated secondary fly ash have been analysed in order to understand the fate of each element. Furthermore, leachable contents of selected elements and total content of persistent organic pollutants of the thermally treated MSWI fly ash were determined. Due to the low total content of Hg (0.7 mg/kg) and the low leachate content of Pb (<0.36 mg/kg), even at the lowest treatment temperature of 450°C, thermally treated MSWI fly ash pellets can be classified as nonhazardous waste. However, temperatures of at least 650°C are necessary to decrease the toxic equivalency of PCDD/F and DL-PCB. The removal of toxic heavy metals like Cd and Pb is significantly improved at temperatures of 850°C, 950°C or even 1050°C. The observed metal removal led to relatively high contents of e.g. Cu (up to 11,000 mg/kg), Pb (up to 91,000 mg/kg) and Zn (up to 21,000 mg/kg) in the secondary fly ash. This metal enriched secondary fly ash might represent a potential raw material for metal recovery (e.g. via acidic leaching). Due to the high content of total dissolved solids observed in the leachate of thermally treated MSWI fly ash pellets, a wet extraction procedure is suggested to enable its safe disposal at non-hazardous waste landfills.
This report gives technological information about processes for the recovery of phosphorus from sewage sludge ash including mass- and energy balance, process conditions and product quality.
The information in this report aim at giving an overview on different concepts for the recovery of phosphorus from sewage sludge ash and are intended to allow a general qualitative comparison between the different technical approaches. This report also describes the technological backgrounds of the processes that were furthermore investigated by life cycle assessment (LCA) and life cycle cost (LCC) analysis. However, most process data stated in this report are site specific data. The LCA/LCC study includes the definition of a common base line for all processes, detailed process modeling and plausibility assessments. Results of the LCA/LCC-studies are reported in deliverables D9.2 und D10.1.
Sewage sludge incineration is extensively practiced in some European countries such as the Netherlands, Switzerland, Austria and Germany. A survey of German sewage sludge ash showed that the recovery potential is high, approx. 19,000 t of phosphorus per year. However, the survey also discovered that the bioavailability of phosphorus in the sewage sludge ash is poor and that more than half of the ashes cannot be used as fertilizers due to high heavy metal content. A new thermochemical process for sewage sludge ash treatment was developed that transforms the ash into marketable fertilizer products. Sewage sludge ash was thermochemically treated with sodium and potassium additives under reducing conditions, whereby the phosphate-bearing mineral phases were transformed into plant available phosphates. High P-bioavailability was achieved with a molar Na/P ratio > 1.75 in the starting materials. Sodium sulfate, carbonate and hydroxide performed comparably as additives for this calcination process. Potassium carbonate and -hydroxide have to be added in a molar K/P ratio > 2.5 to achieve comparable P-solubility. The findings of the laboratory scale investigations were confirmed by an industrial demonstration trial for an ash treatment with sodium sulfate. Simultaneously, the volatile transition metal arsenic (61% removal) as well as volatile heavy metals such as cadmium (80%), mercury (68%), lead (39%) and zinc (9%) were removed via the off-gas treatment system. The product of the demonstration trial is characterized by high bioavailability and a toxic trace element mass fraction below the limit values of the German fertilizer ordinance, thus fulfilling the quality parameters for a P-fertilizer.
Phosphorus fertilizer from sewage sludge ashes by thermochemical treatment - Benefits and challenges
(2015)
Mineral phosphorus (P) fertilizers are solely produced from phosphate rock. Europe completely depends on imports since there are no relevant phosphate rock deposits on the continent. Furthermore, phosphate rock is contaminated with heavy metals such as Cd and U that pollute the farmlands and pose environmental risks. Sewage sludge ash (SSA) might be a promising source for recycling fertilizer since it contains large amounts of P (up to 13 %). However, fertilizer from SSA has to comply with the respective ordinances, particularly the heavy metal limit values stated in the fertilizer ordinance, and requires sufficient P bioavailability. Thus, we conducted a complete survey of SSA from German mono-incineration facilities and developed a thermochemical treatment for SSA to reduce toxic elements and increase P bioavailability.
Municipal sewage sludge is a carrier of nutrients most important phosphorus (P) but also contains organic pollutants and heavy metals. A two steps thermal treatment is suggested based on 1. mono-incineration of sewage sludge under destruction of organic pollutants and 2. thermochemical treatment of the resulting ashes to remove heavy metals and increase P-bioavailability. The targeted products are marketable P-fertilisers. The thermochemical treatment was investigated in a gas tight lab-scale rotary furnace. Seven sewage sludge ashes of different origin and composition and one residue from gasification of sewage sludge were mixed with a chlorine donor (e.g. MgCl2) and thermochemically treated under systematic variation of operational parameters. The distributions of the heavy metals between solid and gas phase were determined. The heavy metals concentrations of the treated ashes met the legislative limits in most cases. The products from thermochemical treatment are suited raw materials for P-fertiliser production. Relevant process parameters such as temperature, type and concentration of Cl-donor and retention time were optimised for the thermochemical treatment step.
Municipal sewage sludge is a carrier of nutrients most important phosphorus (P) but also contains organic pollutants and heavy metals. A two steps thermal treatment based on 1. mono-incineration of sewage sludge under destruction of organic pollutants and 2. thermochemical treatment of the resulting ashes to remove heavy metals and increase P-bioavailability is suggested by the authors. The process aims at P-fertilisers production from sewage sludge. Seven sewage sludge ashes of different origin and composition and one residue from gasification of sewage sludge were thermochemically treated. The raw ashes were mixed with a chlorine donor (e.g. MgCl2) and thermally treated in a gas tight lab-scale rotary furnace. The distributions of the heavy metals between solid and gas phase were determined. The heavy metals concentrations of the treated ashes matched the legislative limits in most cases. The products from thermochemical treatment are suited raw materials for P-fertiliser production. Relevant process parameters such as temperature, type and concentration of Cl-donor and retention time were optimised for the thermochemical treatment step.
Phosphorus (P) is an essential element for all living organisms and cannot be replaced. Municipal sewage sludge is a carrier of phosphorus, but also contains organic pollutants and heavy metals. A two-step thermal treatment is suggested, including mono-incineration of sewage sludge and subsequent thermochemical treatment of the ashes. Organic pollutants are completely destroyed by mono-incineration. The resulting sewage sludge ashes contain P, but also heavy metals. P in the ashes exhibits low bioavailability, a disadvantage in farming. Therefore, in a second thermochemical step, P is transferred into mineral phases available for plants, and heavy metals are removed as well. The thermochemical treatment was investigated in a laboratory-scale rotary furnace by treating seven different sewage sludge ashes under systematic variation of operational parameters. Heavy metal removal and the increase of the P-bioavailability were the focus of the investigation. The present experimental study shows that these objectives have been achieved with the proposed process. The P-bioavailability was significantly increased due to the formation of new mineral phases such as chlorapatite, farringtonite and stanfieldite during thermochemical treatment.
The sequence of reactions accompanying the thermochemical treatment of an iron- and aluminium-bearing sewage sludge ash was ascertained by investigating two systematic series of samples. The ash was thermochemically treated in a lab-scale rotary furnace after mixing it with a chlorine-donor, either CaCl2 or MgCl2. Within each of these two sample series only a single process parameter, the reaction temperature, was varied, namely between 350 and 1050°C. It was found, that among the numerous crystalline phases present in the raw ash only quartz and hematite continue to exist after thermochemical treatments carried out at 1050°C, whereas all other components undergo at least one decomposition-recrystallization cycle. Some of the components re-crystallize even several times. It was proved that the restructuring of the calcium- and phosphorus-bearing mineral phases proceeds via the formation of chlorspodioside, Ca2PO4Cl. The influence of the type of chlorine-donor on the final product was elucidated in detail and - to the best of our knowledge - for the first time crystalline AlPO4 was found in a sewage sludge ash and its decomposition was investigated, too.
The leaching behavior of scandium (Sc) from bauxite residues can differ significantly when residues of different geological backgrounds are compared. The mineralogy of the source rock and the physicochemical environment during bauxitization affect the association of Sc in the bauxite i.e., how Sc is distributed amongst different mineral phases and whether it is incorporated in and/or adsorbed onto those phases. The Sc association in the bauxite is in turn crucial for the resulting Sc association in the bauxite residue. In this study systematic leaching experiments were performed on three different bauxite residues using a statistical design of experiments approach. The three bauxite residues compared originated from processing of lateritic and karstic bauxites from
Germany, Hungary, and Russia. The recovery of Sc and Fe was determined by ICP-OES measurements. Mineralogical changes were analyzed by X-ray-diffraction and subsequent Rietveld refinement. The effects of various parameters including temperature, acid type, acid concentration, liquid-to-solid ratio and residence time were studied. A response surface model was calculated for the selected case of citric acid leaching of Hungarian bauxite residue. The investigations showed that the type of bauxite residue has a strong influence. The easily leachable fraction of Sc can vary considerably between the types, reaching ~20–25% in German Bauxite residue and ~50% in Russian bauxite residue. Mineralogical investigations revealed that a major part of this fraction was released from secondary phases such as cancrinite and katoite formed during Bayer processing of the bauxite.
The effect of temperature on Sc and Fe recovery is strong especially when citric acid is used. Based on the exponential relationship between temperature and Fe-recovery it was found to be particularly important for the selectivity of Sc over Fe. Optimization of the model for a maximum Sc recovery combined with a minimum Fe
recovery yielded results of ~28% Sc recovery at <2% Fe recovery at a temperature of 60 ◦C, a citric acid normality of 1.8, and a liquid-to-solid ratio of 16 ml/g. Our study has shown that detailed knowledge about the Sc association and distribution in bauxite and bauxite residue is key to an efficient and selective leaching of Sc
from bauxite residues.
Phosphorus recycling from sewage sludge will be obligatory in Germany from 2029. Phosphorus content determination in sewage sludge is crucial to assess the prescribed recycling rates. Currently, German law regards sample preparation using aqua regia digestion in a microwave or under reflux conditions as well as instrumental phosphorus determination by ICP-OES, ICP-MS, or photometric determination with ammonium molybdate as equivalent. However, it is questionable whether these methods are indeed equivalent regarding phosphorus quantification in sludges near the limit of 20 g/kg for mandatory recycling. To answer this question, 15 sewage sludges of 11 different wastewater treatment plants were investigated with all permitted method (digestion and measurement) combinations. Moreover, one sewage sludge was also examined in an interlaboratory comparison (ILC) with 28 participants. This study shows that the above-mentioned methods differ in some cases significantly but across all method combinations and sludges, phosphorus recovery was between 80 and 121% after normalization to the grand mean (average of 15 sludges between 85 and 111%). The ILC and the examination of 15 sludges produced largely similar results. There is a tendency to higher phosphorus recovery after microwave digestion compared to reflux digestion and ICP-OES measurements determine higher phosphorus contents than ICP-MS and photometric phosphorus determination. As a result, the authors recommend ICP-OES determination of phosphorus in sewage sludge after microwave digestion.
Phosphorus (P) recovery is obligatory for all sewage sludges with more than 20 g P/kg dry matter (DM) from 2029 in Germany. Nine wastewater treatment plants (WWTPs) were chosen to investigate variations of phosphorus contents and other parameters in sewage sludge over the year. Monthly sewage sludge samples from each WWTP were analyzed for phosphorus and other matrix elements (C, N, H, Ca, Fe, Al, etc.), for several trace elements (As, Cr, Mo, Ni, Pb, Sn) and loss of ignition. Among the nine WWTPs, there are four which have phosphorus contents both above and below the recovery limit of 20 g/kg DM along the year. Considering the average phosphorus content over the year, only one of them is below the limit. Compared to other matrix elements and parameters, phosphorus fuctuations are low with an average of 7% over all nine WWTPs. In total, only hydrogen and carbon are more constant in the sludge.
In several WWTPs with chemical phosphorus elimination, phosphorus fuctuations showed similar courses like iron and/or aluminum. WWTPs with chamber flter presses rather showed dilution efects of calcium dosage. As result of this study, monthly phosphorus measurement is highly recommended to determine whether a WWTP is below the
20 g/kg DM limit.
Phosphorus (P) recovery from sewage sludge ash (SSA) is one of the most promising approaches of phosphate rock substitution in mineral fertilizers and might be a sustainable way to secure supply of this raw material in the future. In the current investigation, the process of thermochemical treatment of SSA was applied to SSA coming from selected mono-incineration plants of municipal sewage sludge in Poland (Cracow, Gdansk, Gdynia, Lodz, Kielce and Szczecin).
The Polish SSA was thermochemically converted in the presence of sodium (Na) additives and a reducing agent (dried sewage sludge) to obtain secondary raw materials for the production of marketable P fertilizers. The process had a positive impact on the bioavailability of phosphorus and reduced the content of heavy metals in the obtained products. The P solubility in neutral Ammonium citrate, an indicator of its bioavailability, was significantly raised from 19.7–45.7% in the raw ashes and 76.5–100% in the thermochemically treated SSA. The content of nutrients in the recyclates was in the range of 15.7–19.2% P2O5, 10.8–14.2% CaO, 3.5–5.4% Na2O, 2.6–3.6% MgO and 0.9–1.3% K2O. The produced fertilizer raw materials meet the Polish norms for trace elements covered by the legislation: the content of lead was in the range 10.2–73.1 mg/kg, arsenic 4.8–22.7 mg/kg, Cadmium 0.9–2.8 mg/kg and mercury <0.05 mg/kg. Thus, these products could be potentially directly used for fertilizer production. This work also includes an analysis of the possibilities of using ashes for fertilizer purposes in Poland, based on the assumptions indicated in the adopted strategic and planning documents regarding waste management and fertilizer production.
Basic oxygen furnace slags (BOFS) are by-products of the steelmaking process. Several researchers have studied the production of Portland cement clinker and metallic iron from BOFS via a reductive treatment.
In this study, we applied a carbothermal reduction of BOFS in a technical-scale electric arc furnace and characterised the clinker-like products. Those clinker-like non-metallic products (NMPs) had a chemical and mineralogical composition comparable to clinker for ordinary Portland cement (OPC) and contained large elongated alite crystals as major component. The pure NMPs reacted more slowly and achieved a lower degree of hydration compared with commercial OPC.
If the reactivity of the products can be further increased by employing specific adaptations, it can be used as a full clinker substitute for OPC. Nevertheless, it is also an option to use the material without further modifications as a cement component or concrete addition, which contributes to the strength development in both cases.
Phase formation and evolution was investigated in the CaO–SiO2 system in the range of 70–80 mol% CaO. The samples were container-less processed in an aerodynamic levitation system and crystallization was followed in situ by synchrotron x-ray diffraction at the beamline P21.1 at the German electron synchrotron (DESY). Modification changes of di- and tricalcium silicate were observed and occurred at lower temperatures than under equilibrium conditions. Despite deep sample undercooling, no metastable phase formation was observed within the measurement timescale of 1 s. For the given cooling rates ranging from 300 K s−1 to about 1 K s−1, no decomposition of tricalcium silicate was observed. No differences in phase evolution were observed between reducing and oxidizing conditions imposed by the levitation gas (Ar and Ar + O2). We demonstrate that this setup has great potential to follow crystallization in refractory oxide liquids in situ. For sub-second primary phase formation faster detection and for polymorph detection adjustments in resolution have to be implemented.
There is an ongoing debate on European scale concerning the criticality of phosphorus. In Switzerland and Germany, phosphorus recovery from phosphorus-rich waste streams will become obligatory. Sewage sludge ash is rich in phosphorus and may become an important secondary feedstock. Thermochemical treatment of sewage sludge ash with sodium sulphate under reducing conditions was shown to remove heavy metals from the solid product and produce the fully plant available crystalline phase CaNaPO4. Pilot-scale experiments in a rotary kiln were carried out at temperatures between 750 and 1000 °C and were compared to laboratory-scale experiments with crucibles. Process upscaling was successfully demonstrated but a series of differences were noticed: In comparison to laboratory-scale, solubility of phosphorus in samples from pilot-scale experiments was lower at all chosen treatment temperatures because of shorter retention time and incomplete decomposition of sodium sulphate. X-ray diffraction analysis revealed remaining phase fractions of whitlockite (Ca3-x(Mg,Fe)x(PO4)2) and sodium sulphate from the starting materials in products and thus indicated incomplete reaction. In contrast to the results of laboratory-scale experiments, the crystalline phase CaNaPO4 was clearly absent in the products from the rotary kiln but instead a Mg-bearing phase (Ca,Mg)NaPO4 was formed. Laboratory-scale experiments confirmed (Ca,Mg)NaPO4 is an intermediate phase between whitlockite and CaNaPO4. However, both crystalline phases are characterized by high plant availability. It was shown that heavy metal removal increased at higher temperatures whereas solubility and thus plant availability of phosphorus already reached its maxima at temperatures of 950 °C in pilot-scale and 875 °C in laboratory-scale experiments.
One of the key elements in the transformation towards a circular economy (CE) is providing more sustainable practices for resources and waste management. Improvement actions focused on transformation towards a CE should be targeted at all groups of materials and waste. As water is essential for human survival and well-being and plays a significant role in sustainable development (SD), the actions related to the reuse of water and the recovery of raw materials from wastewater and other water-based waste should be taken. The paper presents a proposition for a new CE model framework in the water and wastewater sector, which includes the six following actions: reduction—prevent wastewater generation in the first place by the reduction of water usage and pollution reduction at source; reclamation (removal)—an application of effective Technologies for the removal of pollutants from water and wastewater; reuse—reuse of wastewater as an alternative source of water supply (non-potable usage), recycling—recovery of water from wastewater for potable usage; recovery—recovery of resources such as nutrients and energy from water-based waste, and rethink—rethinking how to use resources to create a sustainable economy, which is `free` of waste and emissions. The novelty of the proposed CE model framework is that it presents possible ways of implementing CE principles in the water and wastewater sector, with a strong emphasis not only technological but also organisational and societal changes. Application of the proposed model may help to further transform the European economy to the CE model. Moreover, the indicated model can be significant tool supporting an assessment of local or regional progress towards CE in the water and wastewater sector and further environmental management and planning.
The use of highly water-soluble phosphorus (P) fertilizers can lead to P fixation in the soil, reducing fertilization efficiency. Waste-derived, low water-solubility sources can potentially increase sugarcane’s P uptake compared to triple superphosphate by reducing adsorption to the soil.
Aims:We aimed to test struvite, hazenite, and AshDec® for their agronomic potential as recycled fertilizers for sugarcane production in a typical tropical soil.We hypothesize that these sources can reduce P fixation in the soil, increasing its availability and sugarcane’s absorption.
Methods: In a greenhouse pot experiment, two consecutive sugarcane cycles, 90 days each, were conducted in a Ferralsol. The recovered sources struvite, hazenite, AshDec®, and the conventional triple superphosphate were mixed in the soil in three P doses (30, 60, and 90 mg kg–1), aside a control (nil-P). At both harvests, sugarcane number of sprouts, plant height, stem diameter, dry mass yield, shoot phosphorus, and soil P fractionation were investigated.
Results: At 90 days, struvite and hazenite performed better for dry mass yield (70.7 and 68.3 g pot–1, respectively) than AshDec® and triple superphosphate (59.8 and 57.4 g pot–1, respectively) and for shoot P, with 98.1, 91.6, 75.6, and 66.3 mg pot–1, respectively. At 180 days, struvite outperformed all treatments for dry mass yield (95.3 g pot–1) and AshDec® (75.5 mg pot–1) for shoot P. Struvite was 38% and hazenite 21% more efficient than triple superphosphate in P uptake, while AshDec® was 6% less efficient. Soil had higher labile P under struvite, hazenite, and AshDec® than triple superphosphate by the end of the first cycle, while only the later increased nonlabile P by the end of the experiment (180 days).
Conclusions:Waste-derived P sources were more efficient in supplying P for sugarcane and delivering labile P in 180 days than triple superphosphate.
Phosphorus rich sewage sludge ash is a promising source to produce phosphorus recycling fertilizer. However, the low plant availability of phosphorus in these ashes makes a treatment necessary. A thermochemical treatment (800–1000 °C) with alkali additives transforms poorly plant available phosphorus phases to highly plant available calcium alkali Phosphates (Ca,Mg)(Na,K)PO4. In this study, we investigate the use of K2SO4 as additive to produce a phosphorus potassium fertilizer in laboratory-scale experiments (crucible). Pure K2SO4 is not suitable as high reaction temperatures are required due to the high melting point of K2SO4.
To overcome this barrier, we carried out series of experiments with mixtures of K2SO4 and Na2SO4 resulting in a lower economically feasible reaction temperature (900–1000 °C). In this way, the produced phosphorus potassium fertilizers (8.4 wt.% K, 7.6 wt.% P) was highly plant available for phosphorus indicated by complete extractable phosphorus in neutral ammonium citrate solution. The added potassium is, in contrast to sodium, preferably incorporated into silicates instead of phosphorus phases. Thus, the highly extractable phase (Ca,Mg)(Na,K)PO4 in the thermochemical products contain less potassium than expected. This preferred incorporation is confirmed by a pilot-scale trial (rotary kiln) and thermodynamic calculation.
Conventional phosphate fertilizers are usually highly water-soluble and rapidly solubilize when moistened by the soil solution. However, if this solubilization is not in alignment with plants demand, P can react with the soil colloidal phase, becoming less available over time. This is more pronounced in acidic, oxidic tropical soils, with
high P adsorption capacity, reducing the efficiency of P fertilization. Furthermore, these fertilizers are derived from phosphate rock, a non-renewable resource, generating an environmental impact. To assess these concerns, waste-recycled P sources (struvite, hazenite and AshDec®) were studied for their potential of reducing P Fixation by the soil and improving the agronomic efficiency of the P fertilization. In our work, we compared the solubilization dynamics of struvite, hazenite, AshDec® to triple superphosphate (TSP) in a sandy clay loam Ferralsol, as well as their effect on solution pH and on soil P pools (labile, moderately-labile and non-labile) via an incubation experiment. Leaching columns containing 50 g of soil with surface application of 100 mg per column (mg col 1) of P from each selected fertilizer and one control (nil-P) were evaluated for 60 days. Daily leachate samples from the column were analyzed for P content and pH. Soil was stratified in the end and submitted to P
fractionation. All results were analyzed considering p < 0.05. Our findings showed that TSP and struvite promoted an acid P release reaction (reaching pHs of 4.3 and 5.5 respectively), while AshDec® and hazenite reaction was alkaline (reaching pHs of 8.4 and 8.5 respectively). Furthermore, TSP promoted the highest P release among all sources in 60 days (52.8 mg col 1) and showed rapid release dynamic in the beginning, while struvite and hazenite showed late release dynamics and lower total leached P (29.7 and 15.5 mg col 1 P respectively). In contrast, no P-release was detected in the leachate of the AshDec® over the whole trial period. Struvite promoted
the highest soil labile P concentration (7938 mg kg 1), followed by hazenite (5877 mg kg 1) and AshDec® (4468 mg kg 1), all higher than TSP (3821 mg kg 1), while AshDec® showed high moderately-labile P (9214 mg kg 1), reaffirming its delayed release potential.
Future nutrient recovery from sewage sludge regarding three different scenarios - German case study
(2022)
Agricultural sewage sludge utilization becomes less important in Germany. In 2017, new fertilizer and waste laws caused the agricultural sewage sludge utilization to collapse by more than a quarter. From 2029, German wastewater treatment plants (WWTPs) must recover phosphorus (P) from sewage sludge if it contains more than 2 wt % P. Agricultural utilization will be prohibited for large WWTPs >100,000 population equivalents (pe) from 2029 and >50,000 pe from 2032. In Germany, each federal state must annually report amounts and quality of agriculturally utilized sewage sludge which was 16% of the total disposal in 2019. The reports of 10 states were evaluated for 2016 and 2017 representing approx. 60% of the total agriculturally used sludge volume. In 2016, 60% of the WWTPs’ sludges exceeded the recovery limit of 2 wt % P which is 70% of the amount of sludge and 85% of the phosphorus load. Other nutrients are not affected by the recovery obligation. However, many P recovery processes recover other nutrients, too. Considering three different scenarios for future German sewage sludge disposal shows that 70–77% of the P load in sewage sludge will probably be recovered in the future. At the same time, this applies for about 0–16% nitrogen, 36–52% of calcium, 31–53% of potassium, and 40–52% of magnesium. However, these recovered nutrients loads can substitute only 1% or less of the commercial fertilizer demand except from phosphorus which is up to 43% of the demand.
Gypsum is widely used in the construction sector and its worldwide consumption has been increasing for several decades. Depending on the life-time of the used gypsum products, an increase of gypsum in construction and demolition waste follows. Especially against the background of a circular economy, the recycling of waste gypsum is of growing importance. However, the use of recycled gypsum makes only sense if it is environmentally friendly. Therefore, an evaluation of the environmental impacts of an industrial-scale processing for the recycling of post-consumer gypsum waste was conducted. The evaluation was performed with an established life cycle assessment software. Original data provided by industry and complementary data from a database for life cycle assessments were used for the calculations. Two scenarios for recycled gypsum with different transportation distances were calculated. These results are compared with results of the environmental evaluation of gypsum derived from coal-fired power plants (FGD gypsum) and natural gypsum. The results show that utilization of recycled gypsum can be environmentally advantageous compared to the use of natural gypsum or FGD gypsum, especially in the impact categories land transformation and resource consumption (abiotic depletion potential). For most environmental impact categories the specific transportation distances have a strong influence.
Recycled fertilizers produced using processes for the recovery of phosphate from residual materials such as wastewater, sewage sludge and sewage sludge ashes show very good bioavailability, but it is still a product largely unknown to the market. The aim of CLOOP is therefore to document the properties and effects of such fertilizers through chemical, mineralogical and ecological analyses as well as analytical method development and pot and field plant growth trials.
Outotec focused on 3 points in CLOOP: Experimental campaigns, process simulations as well as economic analyses with focus on the AshDec process, respectively the design of a large-scale AshDec plant for phosphorus recovery. The laboratory scale trials as well as the semi-industrial scale campaign provided valuable insights into the operating parameters of the process and the plant. As a result, for example, the temperature range could be significantly lowered, and the additive addition reduced by approx. 20 %. They have further shown that the AshDec process is not susceptible to operating fluctuations and that the product can be consistently produced at high quality. With the selection of suitable operating parameters, heavy metals (As, Pb, Cd, (Zn)) can be removed. Within the campaign, about 1.5 t of fertilizer for the plant trials in CLOOP could be produced. An AshDec plant process was digitally created in simulation software, allowing valuable process parameters to be simulated at various operating parameters. On this basis, a full-scale plant was designed. The data obtained in the project were used for a detailed economic analysis including a sensitivity analysis. It was possible to show under which conditions this plant can be operated economically.
At BAM, the AshDec fertilizer was synthesized with different additives and then applied to plant experiments at Uni Bonn. The goal hereby was to check differences in plant uptake. Because of the promising results of AshDec synthesized with sodium-carbonate and because this AshDec version does not require special off gas treatment for sulfur recovery (compared to AshDec synthesized with sodium-sulfate), all project partners agreed on continuing working with this AshDec variation. It was then used as a raw P-source for formulating it into NPK-fertilizers, by granulation with ammonium-sulfate and straw ash as potassium source. These recycling fertilizers were applied to plant- and field experiments by project partners in Brazil (University of Sao Paulo) and Australia (University of Queensland). Furthermore, in leaching experiments, the solubility of phosphorus in AshDec was compared to triple super phosphate. The experiments were carried out on soils with a varying phosphorus buffering index. Results show, that the phosphorus form in AshDec is way less soluble in water. This indicates that AshDec has the potential for a so-called next generation fertilizer – a fertilizer which’s nutrients remain in the soil and supply the plant according to its needs. At the moment, this behavior gets examined more in depth in lysimeter experiments in cooperation with University of Technology Berlin.
The focus of KWB is the Life Cycle Assessment (LCA) of different NextGen fertilizers to evaluate the entire process chain from recovery to fertilizer application. The NextGen fertilizer is credited by the amount of plant available nutrients in the product, which replace nutrients from conventional fertilizer. The LCA covers N-struvite precipitation from municipal wastewater, K-struvite precipitation from industrial wastewater and the AshDec-product from sewage sludge. The LCA task is almost complete. It could be shown that struvite precipitation has comprehensive environmental benefits, mainly since positive side effects occur in sewage sludge treatment (e.g. reduced sludge volume). In principle, the energetic and ecological profile of the AshDec process compared to direct use of sewage sludge ash cannot be assessed as being generally beneficial or negative. Regarding the global warming potential, the Ashdec process shows that the expenses (e.g. energy, chemicals) cannot be covered by the P fertilizer credit. In contrast, the impact categories “terrestrial acidification potential”, and “freshwater eutrophication potential” show positive results as the credits for conventional fertilizer are higher than the burdens for the process.
At University Bonn, the standardized pot experiments were conducted with several AshDec variations, using ryegrass, soybean, and spinach on a slightly acidic sandy soil and an organic-free standard substrate. P-uptake and biomass production of different AshDec variations were generally like those of triple super phosphate and struvite, and clearly outperformed untreated sewage sludge ash and rock phosphate. Field trials in Australia and Brazil with sugarcane on acidic soils are still ongoing and results are expected by the end of 2021.
During the last decades the material composition of buildings has become increasingly diverse. However, largely sorted material flows are needed for generating high quality secondary building materials. The use of secondary building materials can meet the requirements of sustainability in several ways: the extended time availability of primary raw materials and, thereby, the preservation of natural resources as well as the conservation of landfill sites.
Recycling of gypsum (calcium sulfate) can be a good example for the environmental benefits of closed-loop recycling. The content of sulfates in other secondary building materials, in particular in recycled concrete aggregates, should be minimized for quality reasons. In contrast, separated gypsum can also be used in gypsum production if the high quality requirements for the recycled gypsum are met. Since almost all processing steps in the recycling process are associated with environmental impacts, an environmental evaluation of the use of recycled gypsum as a substitute in gypsum production has to be carefully conducted.
This paper focusses on the techniques for generating recycled gypsum from gypsum plasterboards, the related quality requirements and a comprehensive environmental evaluation of the complete process.
Blast furnace (BF) sludge and electric arc furnace (EAF) dust are typical wastes that incur from iron and steel production. In addition to iron, calcium, carbon, and silicon they usually contain high concentrations of heavy metals such as zinc, lead, and cadmium that are potentially hazardous to the environment, rendering disposal in landfills ecologically problematic and costly. Consequently, pyrometallurgical, hydrometallurgical, and hybrid methods for selective elimination of non-ferrous heavy metals from BF sludge and EAF dust have been conceived, of which only the carbothermic reduction route taken in the so-called Waelz rotary kiln process has been proven to be economically successful. However, this process has several drawbacks regarding efficiency of heavy-metal removal and recovery of iron, and it does not allow processing of BF sludge. In this study, we investigated the efficiency and feasibility of selective chlorination and evaporation of non-ferrous heavy metals, particularly zinc and lead, in both BF sludge and EAF dust as an alternative, thermochemical processing route. To this end, hydrochloric acid and iron(II) chloride solution have been used as chlorinating agents, and the process of heavy-metal chlorination and evaporation has been investigated under inert operating conditions, at variable chlorine concentrations, and at temperatures between 500 and 1200 °C.
High zinc and lead removal efficiencies of > 99.5 % were achieved with both chlorinating agents, but iron(II) chloride turned out to be overall more efficient for removal of zinc and lead from BF sludge and EAF dust. Interestingly, and in contrast to previous studies, the iron was completely retained in the processed solid residue, therefore rendering the processed residues virtually zinc- and lead-free raw materials that may either be used internally (e.g., feeding processed BF sludge and EAF dust back into the respective furnaces) or externally (e.g., for cement production).
An existing pyrometallurgical process for tantalum and niobium recovery, mainly from low grade pyrometallurgical residues, was investigated. Series of melting experiments were carried out in a pilot-scale electric arc furnace to study how the amount, the grain size and the way of feeding affect the activity of carbon as a reducing agent. During the pyrometallurgical treatment refractory metals such as tantalum and niobium are reduced to their carbide form and enriched in the molten iron-based metal phase. The cooled down slag and metal phase were analysed to investigate thermodynamic and kinetic conditions of the carbide formation. FACT Sage simulations were also used to investigate the material system in state of thermodynamic equilibrium. Results show that mass transfer and kinetics may play an important role if compared to equilibrium analyses using FACT Sage.