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Paper des Monats
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The plant-availability of phosphorus (P) in fertilizers and soil can strongly influence the yield of agricultural crops. However, there are no methods to efficiently and satisfactorily analyze the plant-availability of P in sewage sludge-based P fertilizers except by undertaking time-consuming and complex pot or field experiments. We employed the diffusive gradients in thin films (DGT) technique to quantify the plant P availability of various types of P fertilizers with a novel focus on sewage sludge-based P fertilizers. Mixtures of fertilizer and soil were incubated for 3 weeks at 60% water holding capacity. DGT devices were deployed at the beginning of the incubation and again after 1, 2, and 3 weeks. Two weeks of incubation were sufficient for the formation of plant-available P in the fertilizer/soil mixtures. In a pot experiment, the DGT technique predicted maize (Zea mays L.) biomass yield and P uptake significantly more accurately than standard chemical extraction tests for P fertilizers (e.g., water, citric acid, and neutral ammonium citrate). Therefore, the DGT technique can be recommended as a reliable and robust method to screen the performance of different types of sewage sludge-based P fertilizers for maize cultivation minimizing the need for time-consuming and costly pot or field experiments.
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.
A pot experiment was carried out with maize to determine the phosphorus (P) plant-availability of different secondary P-fertilizers derived from wastewater. We analyzed the respective soils by P K-edge X-ray absorption near-edge structure (XANES) spectroscopy to determine the P chemical forms that were present and determine the transformation processes. Macro- and micro-XANES spectroscopy were used to determine the chemical state of the overall soil P and identify P compounds in P-rich spots. Mainly organic P and/or P adsorbed on organic matter or other substrates were detected in unfertilized and fertilized soils. In addition, there were indications for the formation of ammonium phosphates in some fertilized soils. However, this effect was not seen in the maize yield of all P-fertilizers. The observed reactions between phosphate from secondary P-fertilizers and cofertilized nitrogen compounds should be further investigated. Formation of highly plant-available compounds such as ammonium phosphates could make secondary P-fertilizers more competitive to commercial phosphate rock-based fertilizers with positive effects on resources conservation.
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.
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 plant-available soil P species, we combined DGT with infrared and P K- and L-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. Additionally, also intermediates of the time-resolved hydrolysis of trimetaphosphate in soil could be analyzed. Furthermore, infrared and XANES microspectroscopy make it also possible to analyze P compounds on the binding layer with a lateral resolution down to 1 µm2. Therefore, P species of a spatial soil segment (e.g. rhizosphere) can be mapped and analyzed.
Recycling-Düngemittel auf Basis von sekundären Ressourcen (Gülle, Gärreste, Klärschlamm, Tiermehl etc.) gewinnen in den letzten Jahren zunehmend an Bedeutung in der Landwirtschaft. Die in den Recycling-Düngemitteln enthaltenen P-Spezies weichen oft stark von denen in konventionell hergestellten Düngemitteln aus Rohphosphat ab, zudem enthalten Recyclingdünger oft mehrere verschiedene P-Formen. Die Pflanzenverfügbarkeit des P in ist ganz wesentlich von der enthaltenen P-Form abhängig. Derzeit gibt es außer zeitaufwendigen und kostspieligen Gefäß- und Feldversuchen keine zufriedenstellende Testmethode zur Analyse der P-Pflanzenverfügbarkeit von unterschiedlichen Recycling P-Düngemitteln. Die im europäischen Düngemittelrecht normierten chemischen Extraktionsmethoden (Wasser, Zitronensäure, Ameisensäure, neutral Ammoniumcitrat etc.) zeigen oftmals keine oder nur sehr geringe Korrelation zu der P-Aufnahme von Pflanzen in Gefäßversuchen mit Recycling-Düngemitteln (Kratz et al. 2010, Steckenmesser et al. 2017, Vogel et al. 2017). Eine grundlegende Schwäche chemischer Extraktionsmethoden liegt darin, dass es sich dabei um statische Methoden handelt, die nicht in der Lage sind, die im System Boden/Düngemittel-Bodenlösung-Pflanze stattfindenden dynamischen Prozesse wie P-Freisetzung und Entzug durch die Pflanzenwurzeln abzubilden.
Einen Lösungsansatz bieten hier sog. P-Senken-Methoden. Bereits in den 1950er Jahren wurden erstmals P-Senken zur Analyse des Boden-P angewendet (Chardon et al. 1996). In den darauffolgenden Jahrzehnten wurden verschiedene P-Senken auf der Basis von Eisenoxid-Papier entwickelt (Chardon et al. 1996). Jedoch konnten diese Ansätze auch nur begrenzt zur Bestimmung der P-Pflanzenverfügbarkeit des Boden-P eingesetzt werden. Mitte der 1990er Jahre wurde die DGT (engl. diffusive gradients in thin films) Methode entwickelt (Zhang et al. 1998). Bei der DGT Methode diffundiert P aus der Bodenlösung des angefeuchteten Bodens durch einen Membranfilter und die Diffusionsschicht und wird anschließend an einer Bindungsschicht absorbiert. Durch den Diffusionsgradienten wird das Gleichgewicht in der Bodenlösung permanent gestört, wodurch auch labiles P im Boden gelöst wird. Die stetige Entnahme von P aus der Bodenlösung über die Diffusions-/Bindungsschicht simuliert dabei den Entzug von P durch die Pflanzenwurzel. Die an die Bindungsschicht adsorbierte Menge an P korreliert stark mit der P-Aufnahme von Pflanzen (u.a. Mason et al. 2005, 2013; Menzies et al. 2005, Six et al. 2012). Im Gegensatz zu chemischen Extraktionsmethoden werden bei der DGT Methode Mischungen an Düngemittel und Boden für mehrere Tage inkubiert (Vogel et al. 2017; Duboc et al. 2017), da ansonsten wasserlösliche P-Dünger den DGT Adsorber sättigen und wasserunlösliche P-Dünger unterschätzt werden. Ein bis zwei Wochen Inkubation sind ausreichend, damit sich pflanzenverfügbares P in die Mischungen bildet.
In letzter Zeit haben verschiedene Forschungsgruppen gezeigt, dass die DGT Methode auch eine sehr gute Korrelation mit der Pflanzenverfügbarkeit verschiedener Typen von (Recycling-)P-Düngemitteln aufweist (Vogel et al. 2017; Duboc et al. 2017; Foereid 2017; Haarstad and Bavor 2017; Lemming et al. 2017). Bei Gefäßversuchen mit verschiedenen Recycling P-Düngemitteln konnte die DGT Methode den Ertrag bzw. die P-Aufnahme von Mais deutlich besser vorhersagen als herkömmliche chemische Extraktionsmethoden (Vogel et al. 2017; Duboc et al. 2017).
Daher kann die DGT Methode im Vorfeld der Zulassung von neuen Düngermitteltypen als zuverlässige und robuste Methode zum Screening von Produktvarianten eines Düngemittelherstellers verwendet werden. Um dieses Messverfahren im Rahmen des Düngemittelrechts als Bewertungsinstrument für die Abschätzung der Pflanzenverfügbarkeit unterschiedlicher Düngemittel zu verwenden, muss es allerdings zunächst standardisiert werden. Zu diesem Zweck bietet sich der Einsatz eines „standardisierten“ Bodens bzw. Bodenrezepts an. Zur Kalibrierung der Methode im jeweiligen Labor könnten auch chemisch definierte P-Verbindungen mit bekannter Löslichkeit/Pflanzenverfügbarkeit als Referenz-substanzen verwendet werden.
Phosphorus (P) plays an essential role in the global food security. However, the global P reservoirs have a statistic lifetime of about 385 years only. Due to the scarcity of P and the increasing world population an efficient and sustainable recycling management is required. A few biogenic waste materials are high in P contents such as sewage sludge and meat and bone meal. Thus, they are suitable for P recycling and fertilizer production. But besides the high P content sewage sludge is often highly contaminated with organic pollutants and toxic heavy metals which have to be eliminated before agricultural field application. In this presentation we show the potential of sewage sludge as secondary resource for fertilizers. This includes our developments in thermochemical processes for the production of novel P-fertilizers from recycled materials. Furthermore, for these novel P-fertilizers common extraction tests to determine the plant-available P are often unusable. Therefore, we successfully applied the Diffusive gradients in thin-films (DGT) techniques to analyse the plant-availability of P-fertilizers from recycled materials.
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.
Characterization of phosphorus compounds in soils by deep ultraviolet (DUV) Raman microspectroscopy
(2017)
Deep ultraviolet Raman microspectroscopy was successfully investigated as a new approach to analyze the chemical state of phosphorus compounds directly in soil. We demonstrate that ultraviolet excitation has the advantage to avoid the interference with the strong fluorescence, which occurs in the visible spectral range caused by organic matter in soils. Furthermore, the spatial resolution of <1 μm2 enables the detection of very small phosphorus particles. For some organic phosphorus compounds (β-glycerophosphate, aminomethylphosphonic acid), sample cooling to -100 °C is found to strongly reduce the rate of degradation induced by the illumination with the ultraviolet excitation light. However, phytic acid and adenosine monophosphate degraded even with cooling. Our results reveal the capability of deep ultraviolet Raman microspectroscopy as a high-resolution benchtop imaging technique for the analysis of local interactions between soil compounds with the potential to become an analytical key to improve the understanding of transformation mechanisms of phosphates as well as other mineral phases in soils.
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.