Résumé:
Phosphate rock is a depleting resource and wastewater a sustainable long-term alternative for phosphorous mining. In modern wastewater treatment phosphate is concentrated 7500 times from wastewater into sludge as iron phosphate (FeP). Recently developed bioelectrochemical reactors enabled phosphate recovery from sewage sludge containing FeP. The integrated bioelectric process was found of much broader utility than initially elaborated. It refines all principle components of wastewater. The implementation is confronted to a number of challenges. Three pilot microbial electrolysis cells (MECs) of 168 L each were constructed and installed in different municipal wastewater treatment plants (WWTPs). The scale-up MECs generated renewable chemical base and co-extracted abundant species such as Na+, K+, Ca2+, Mg2+ and NH4+ from wastewater. The chemical base remobilized phosphate quantitatively from iron phosphates contained in digested sewage sludge. Phosphate extracts contained ammonia and upon magnesium (Mg2+) addition struvite crystalized. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) on heavy metals, Direct Mercury Analysis (DMA), Liquid Chromatography Mass Spectroscopy (LC-MS/MS) on organic micropollutants, metagenomics sequencing, Scanning Electron Microscopy (SEM-EDS), and X-Ray Diffraction (XRD) indicated that a highly pure struvite-fertilizer was produced. Microbial electricity co-generation was verified by electrochemical characterisation and microbiome analysis using 16S rRNA V4-V5 methodology. Geobacter, Dechloromonas, Desulfobulbus and cyanobacteria were the principal electrogens found. All in all, renewable chemical base as well as phosphate were obtained in high quantities and other renewables became accessible such as the critical material magnesium and other compounds of importance like ammonia, potassium, calcium, solid P-free sludge useful as biofuel and purified water. In general, the process recycles important compounds from waste, in a close to traceless manner while purifying wastewater.
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