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Eingeladener Vortrag
- nein (16)
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.
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.
Klärschlammaschen weisen hohe Gehalte an Phosphor auf, dieser ist allerdings schlecht für Pflanzen verfügbar. Des Weiteren enthalten sie Schwermetalle die vor dem Einsatz als Düngemittel entfernt werden müssen. Vor diesem Hintergrund wurden in den letzten Jahren nasschemische und thermochemische Verfahren entwickelt und zum Teil bereits in Demonstrationsanlagen getestet. Ein thermochemischer Verfahrensansatz wird in diesem Beitrag näher vorgestellt. Klärschlammaschen werden mit Klärschlamm als Reduktionsmittel und Natriumsulfat als Aufschlussmittel im Drehrohrofen thermisch behandelt. Bei diesem Prozess wird pflanzenverfügbares NaCaPÜ4 gebildet, unerwünschte Elemente wie As, Cd, Hg und Pb werden zum Teil über die Gasphase separiert. Die Ergebnisse eines Demonstrationsversuchs werden vorgestellt.
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.
Phosphorus Fertilizer from Sewage Sludge Ashes by thermochemical treatment - Benefits and Challenges
(2015)
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.
Aufgrund der natürlichen und vom Menschen verursachten Heterogenität von Böden erfordert der Erhalt und die Verbesserung ihrer Fruchtbarkeit durch landwirtschaftliche Bewirtschaftungsmaßnahmen sorgfältig geplante Ent-scheidungen, die auf einer detaillierten Erfassung der Bodeneigenschaften und einem vertieften Verständnis der Bodenprozesse beruhen. Es ist bekannt, dass die konventionelle, flächen-einheitliche Bewirtschaftung Ertragsver-luste durch zu geringe Bewirtschaftungsintensität (z. B. Düngung) auf einen Teil der Fläche verursacht, während andere Teile des Feldes zu hohe Dosen erhalten und es dadurch zu Verschwendung von Ressourcen und zu Um-weltbelastungen kommt. Trotz der Verfügbarkeit von Technologien für ortsspezifische Düngung ist die Akzeptanz ortsspezifischer Bewirtschaftung (Precision Agriculture) in der Praxis noch gering. Ein wesentlicher Grund dafür ist das Fehlen von kostengünstigen Methoden zur Erfassung der bewirtschaftungsrelevanten Bodenmerkmale. So-wohl für die elementanalytische Untersuchung von Böden als auch für die Untersuchung von Ausgangsmaterialien (z.B. Klärschlammaschen) für ihre Verwendung als Dünger ist eine zuverlässige Analytik und Prozessüberwachung erforderlich.