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Title Recovery of phosphates as struvite from urine-diverting toilets: optimization of pH, Mg:PO4 ratio and contact time to improve precipitation yield and crystal morphology
ID_Doc 10062
Authors Rodrigues, DM; Fragoso, RD; Carvalho, AP; Hein, T; de Brito, AG
Title Recovery of phosphates as struvite from urine-diverting toilets: optimization of pH, Mg:PO4 ratio and contact time to improve precipitation yield and crystal morphology
Year 2019
Published Water Science And Technology, 80.0, 7
Abstract Phosphate (P) recovery from urban wastewaters is an effective strategy to address environmental protection and resource conservation, aiming at an effective circular economy. Off-grid wastewater treatment systems like urine-diverting toilets (UDT) can contribute to source separation towards nutrient recovery, namely phosphorus recovery. Effectiveness of P precipitation requires a process-based knowledge regarding pH, Mg:PO4, contact time and their interactions in P recovery and crystal morphology. Several studies failed to see the process as a whole and how factors influence both morphology and P recovery for UDT hydrolysed urine. This study addressed the above-mentioned factors and their interactions, and results showed that pH and Mg:PO4 ratio are the key factors for struvite precipitation, whereas contact time is relevant for crystal growth. The recommended set of factors proposed (pH 8.5, Mg:PO4 ratio of 1.2:1 and 30 minutes contact time) not only promotes a high precipitation yield - 99% of P with co-precipitation of at least 21% of ammonium (NH4+) - but also leads to larger crystals with lower water solubility (10% less crystals dissolved in water after 3 days). The obtained outcome facilitates the downstream process and leads to a more efficient slow-release fertiliser, as less P is wasted to receiving waters by leaching, minimising eutrophication processes.
PDF https://iwaponline.com/wst/article-pdf/80/7/1276/637311/wst080071276.pdf

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