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Heavy metal removal from sewage sludge ash by thermochemical treatment with polyvinylchloride
(2013)
Sewage sludge ash (SSA) is a prospective phosphorus source for the future production of recycling P-fertilizers. Due to its high heavy metals contents and the relatively low P plant-availability, SSA must be treated before agricultural utilisation. In this paper SSA was thermochemically treated with PVC in a bench-scale rotary furnace in order to remove heavy metals via the chloride pathway. PVC has a high Cl-content of 52–53% and a high heating value that can be beneficially used for the thermochemical process. Large amounts of waste PVC are already recovered in recycling processes, but there are still some fractions that would be available for the proposed thermochemical process, for example, the low quality near-infrared(NIR)-fraction from waste separation facilities. Heavy metals were effectively removed at temperatures in the range of 800–950°C via the gas phase by utilisation of PVC as Cl-donor. The resulting P plant-availability was comparable to SSA thermochemically treated with MgCl2 as Cl-donor if MgO was used as an additive (Mg-donor). A further increase of the plant availability of phosphorus was achieved by acid post-treatment of the thermochemically treated SSA.
Determination of phosphate phases in sewage sludge ash-based fertilizers by Raman microspectroscopy
(2013)
The chemical form of phosphate phases in sewage sludge ash (SSA)-based fertilizers was determined by Raman microspectroscopy. Raman mapping with a lateral resolution of 5 × 5 µm² easily detected different compounds present in the fertilizers with the help of recorded reference spectra of pure substances. Quartz and aluminosilicates showed Raman bands in the range of 450-520 cm-1. Phosphates with apatite structure and magnesium triphosphate were determined at around 960 and 980 cm-1, respectively. Furthermore, calcium/magnesium pyrophosphates were detected in some samples.
The reaction mechanisms of phosphate-bearing mineral phases from sewage sludge ash-based fertilizers in soil were determined by Raman and synchrotron infrared microspectroscopy. Different reaction mechanisms in wet soil were found for calcium and magnesium (pyro-) phosphates. Calcium orthophosphates were converted over time to hydroxyapatite. Conversely, different magnesium phosphates were transformed to trimagnesium phosphate. Since the magnesium phosphates are unable to form an apatite structure, the plant-available phosphorus remains in the soil, leading to better growth results observed in agricultural pot experiments. The pyrophosphates also reacted very differently. Calcium pyrophosphate is unreactive in soil. In contrast, magnesium pyrophosphate quickly formed plant-available dimagnesium phosphate.
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.
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.
The diffusive gradients in thin-films (DGT) technique shows in many publications a superior correlation to the amount of plant-available phosphorus (P) in soil. However, this technique cannot give information on the plant-available P species in soil. Therefore, we combined DGT with solution 31P nuclear magnetic resonance (NMR) spectroscopy. This was achieved by using a modified DGT device in which the diffusive layer had a larger pore size, the binding layer incorporated an adsorption material with a higher capacity, and the device had a larger exposure area. The spectroscopic investigation was undertaken after elution of the deployed DGT binding layer in a NaOH solution. Adsorption tests using solutions of known organic P compounds showed that a sufficient amount of these compounds could be adsorbed on the binding layer in order for them to be analyzed by solution 31P NMR spectroscopy. Furthermore, various intermediates of the hydrolysis of trimetaphosphate in soil could be also analyzed over time.
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.
SR-FTIR in combination with Principal Component Analysis (PCA) was applied to investigate macromolecular changes in a population of melanocytes and their extracted nuclei induced by environmentally relevant fluxes of UVR (Ultraviolet Radiation). Living cells and isolated cellular nuclei were investigated post-irradiation for three different irradiation dosages (130, 1505, 15 052 Jm-2 UVR, weighted) after either 24 or 48 hours of incubation. DNA conformational changes were observed in cells exposed to an artificial UVR solar-simulator source as evidenced by a shift in the DNA asymmetric phosphodiester vibration from 1236 cm-1 to 1242 cm-1 in the case of the exposed cells and from 1225 cm-1 to 1242 cm-1 for irradiated nuclei. PCA Scores plots revealed distinct clustering of spectra from irradiated cells and nuclei from non-irradiated controls in response to the range of applied UVR radiation doses. 3D Raman confocal imaging in combination with k-means cluster analysis was applied to study the effect of the UVR radiation exposure on cellular nuclei. Chemical changes associated with apoptosis were detected and included intra-nuclear lipid deposition along with chromatin condensation. The results reported here demonstrate the utility of SR-FTIR and Raman spectroscopy to probe in situ DNA damage in cell nuclei resulting from UVR exposure. These results are in agreement with the increasing body of evidence that lipid accumulation is a characteristic of aggressive cancer cells, and are involved in the production of membranes for rapid cell proliferation.
Synchrotron Radiation Fourier Transform Infrared (SR-FTIR) spectra of single human prostate adenocarcinoma PC-3 cells, irradiated with a defined number of 2 MeV protons generated by a proton microbeam along with non-irradiated control cells, were analysed using multivariate methods. A number of different Principal Component Analysis (PCA) models were tested and the spectral ranges associated with nucleic acids, proteins and lipids were analysed separately. The results show a dose dependent shift of the O—P—O asymmetric stretching mode from 1234 cm-1 to 1237 cm-1, consistent with local disorder in the B-DNA conformation along with a change in intensity of the O—P—O symmetric stretching band at 1083 cm-1 indicative of chromatin fragmentation the natural consequence of a high number of DNA Double Strand Breaks (DSBs). 2D mapping of characteristic functional groups at the diffraction limit shows evidence of lipid deposition and chromatin condensation in cells exposed to protons indicative of cell apoptosis following irradiation. These studies lay the foundation for understanding the macromolecular changes that occur to cells in response to radiation therapy, which has important implications in the treatment of tumours.
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.
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.
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.
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.
Thermal treatment of chromium (III) oxide with carbonates analyzed by far-infrared spectroscopy
(2015)
SR-FTIR Coupled with principal component analysis shows evidence for the cellular bystander effect
(2015)
Synchrotron radiation-Fourier transform infrared (SR-FTIR) microscopy coupled with multivariate data analysis was used as an independent modality to monitor the cellular bystander effect. Single, living prostate cancer PC-3 cells were irradiated with various numbers of protons, ranging from 50–2,000, with an energy of either 1 or 2 MeV using a proton microprobe. SR-FTIR spectra of cells, fixed after exposure to protons and nonirradiated neighboring cells (bystander cells), were recorded. Spectral differences were observed in both the directly targeted and bystander cells and included changes in the DNA backbone and nucleic bases, along with changes in the protein secondary structure. Principal component analysis (PCA) was used to investigate the variance in the entire data set. The percentage of bystander cells relative to the applied number of protons with two different energies was calculated. Of all the applied quantities, the dose of 400 protons at 2 MeV was found to be the most effective for causing significant macromolecular perturbation in bystander PC-3 cells.
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.