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Ressourcen aus Abfall
(2012)
Die Beseitigung unbehandelter Abfälle auf Deponien gehört der Vergangenheit an, nicht nur weil Verordnungen diese Praxis verbieten, sondern auch, weil wegen steigender Preise für Rohstoffe und sinkender Gehalte in Erzen auch in Abfällen nach Alternativen gesucht wird. In den Aschen aus Hausmüllverbrennungsanlagen können mit einfachen Verfahren Metalle zurückgewonnen werden. Mit dem Phosphor aus Klärschlammaschen können Düngemittel hergestellt und so natürliche Ressourcen geschont werden. In beiden Fällen ist die Anreicherung der Wertstoffe durch den Verbrennungsprozess vorteilhaft, da die Effizienz von Recyclingprozessen stark von der Konzentration im Ausgangsgut abhängig ist.--------------------------------------------------------------------------------------------------------------------------------
Disposal of untreated waste has come to end due to new legislation in this field. Furthermore as a response to increasing prices for primary raw materials and decreasing ore concentrations products from waste treatment display a source for secondary raw materials. Elemental metals can be easily separated from municipal solid waste incineration bottom ash. Fertilizers can be produced using phosphate from sewage sludge ashes thus preserving natural resources. In both cases the enrichment taking place in the incineration process facilitates the resource recovery, because the efficiency of recycling processes is dependent on the concentration of the input material.
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.
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.
Für die Entfernung von VOC (volatile organic compounds) aus der Luft von Fertigungsstätten werden vielfach mikroporöse Adsorbentien eingesetzt. Die gereinigte Luft wird rezyklisiert. Für die mit VOC beladenen Adsorbentien wird ein Regenerierungsweg für den mehrfachen Gebrauch gesucht. Bei der Regenerierung sollen die VOC möglichst vollständig desorbiert werden und mit einer geringen Gasmenge in einer katalytischen Verbrennung zu CO2 und H2O umgewandelt werden. Die Wirtschaftlichkeit der Luftreinigung wird wesentlich bestimmt durch die Sorptionskapazität des Adsorbens, die erforderliche Energie für die thermische Regenerierung und die Menge des Spülgases bei der Regenerierung. In dieser Arbeit wird der Einsatz von Typ X-Zeolithpulver in der Luftreinigung einer Lackiererei beschrieben und dessen Regenerierung im Labor mittels DTA/TG und Isothermenmessung der Schlüsselkomponenten untersucht. Ferner wurde die Regenerierung des beladenen Zeoliths in einem Labor-Drehrohrofen unter Variation der Betriebsparameter untersucht und anschließend mit ausgewählten Parametern in einem kleintechnischen Drehrohrofen durchgeführt. Die Verfahrensvarianten werden diskutiert.
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.
Phosphor ist ein für alle Lebewesen essenzielles Element und kann in seinen Funktionen z. B. als Bestandteil der DNS und RNS sowie als Schlüsselelement beim Energiestoffwechsel (ADP/ATP) nicht ersetzt werden. Klärschlammaschen sind aufgrund ihrer hohen Gehalte an Phosphor (1525 % P2O5) geeignete Sekundärrohstoffe für die Herstellung von P-Düngemitteln. Aufgrund der schlechten Pflanzenverfügbarkeit des Phosphors und der Gehalte an umweltrelevanten Schwermetallen sollten diese allerdings nicht direkt in der Landwirtschaft eingesetzt werden. Im Mittelpunkt des EU-Projekts SUSAN steht die Entwicklung und Optimierung einer thermochemischen Behandlung von Klärschlammaschen, mit der die Düngewirkung der Aschen auf das Niveau konventioneller Mineraldünger (Thomaskali und Superphosphat SSP) angehoben wird und die Schwermetallkonzentrationen unter die Grenzwerte nach Düngemittelverordnungen europäischer Länder abgesenkt werden. Die sehr positiven Ergebnisse, die bisher im SUSAN-Projekt erzielt wurden, und die darauf basierenden ökonomischen Betrachtungen legen eine großtechnische Umsetzung des Verfahrens nahe.
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.
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.