Reference : Rückgewinnung von Pflanzennährstoffen, insbesondere Phosphor aus der Asche von Klärschlamm
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Engineering, computing & technology : Chemical engineering
Rückgewinnung von Pflanzennährstoffen, insbesondere Phosphor aus der Asche von Klärschlamm
[en] Recovery of plant nutriens, especially phosphorous from the ash of sewage sludge
Doetsch, Peter []
Pinnekamp, Johannes []
Rath, Walter []
Grömping, Markus []
Pfennig, Andreas mailto [Université de Liège > Department of Chemical Engineering > PEPs - Products, Environment, and Processes >]
Kröckel, Jan []
Abdellatif, Tarek []
Bundesministerium für Bildung und Forschung
[en] phosphosrous ; process development ; recycle
[en] The project's objective was to develop a process to recover phosphorus from sewage sludge ash. As a first step, thermal processes and recycling methods, such as metallurgical processes and mechanical treatment (e.g. flotation, gravity and magnetic separation), were examined to achieve a further accumulation of the phosphorus in the ash. This work shows general improvement possibilities in the overall process of sludge incineration and recovery of phosphorus.
Laboratory-scale and pilot plant experiments led to the development of a recovery process. It is based on three steps: Chemical leaching of the ash, purification of the emerging solution and product precipitation. In order to release phosphate from sewage sludge ash, it is mixed in a vessel with diluted hydrochloric acid at ambient temperature. Afterwards the leachate is separated from the remaining residuum (solids) which will be washed and freed from the wash water. The chloric leachate is treated in a multilevel solvent extraction process to separate the dissolved metals, which are to be found as chlorinated complexes. This extraction should be carried out in a two-stage mixer-settler unit. The extracting agent (containing the metal ions) is washed and the metals become re-extracted; thus the agent can be recycled after protonation. As a last step the product is precipitated from the raffinate.
Different products can be generated; thus a raw material and product related optimization is possible during a large-scale operation without serious change in construction or machines. The PASH process allows producing a magnesium phosphate and two different calcium phosphates, which contain rather low amounts of metals and guarantee the plant availability of phosphorus.
Besides the chemical leaching process, a bioleaching of the ashes by induced bacteria and a selective bioaccumulation in biomass was explored. These results might become transferred to an alternative phosphorus recovery process in the future.
The results from the laboratory-scale and pilot-scale experiments have been used for a calculation of investment and operational costs. A life-cycle analysis shows clear ecological advantages of the PASH process compared to the production of primary phosphate fertilizer.

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Doetsch Pinnekamp et al. 2010 Rückgewinnung von Pflanzennährstoffen, insbesonde Phosphor aus der Asche von Klärschlamm.pdfAuthor postprint9.42 MBRequest copy

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