Abstract
Human urine can be diverted from faeces by urine diversion toilets. Nutrient recovery from diverted urine has been a growing concern recently, because urine contains many nutrients. Phosphorus in urine can be recovered as a precipitate of MAP (i.e., struvite, MgNH4PO4·6H2O) by adding magnesium salt under alkaline conditions. In this study, we (1) developed a plant for struvite recovery from urine using a urine diversion toilet, (2) investigated the characteristics of the plant's urine collection, urine storage and struvite formation, and (3) analyzed the precipitates formed in the plant. In this report, we present the phosphorus flow in the plant. The plant was mainly composed of a urine diversion toilet, a storage tank and a reactor. Using the toilet, 94.8% of the urine excreted into the toilet was collected and stored in the storage tank. The composition of the stored urine became stable 19 days after the start of urine storage, and 20.8% of the phosphorus in the urine excreted into the toilet was precipitated with other precipitates during urine storage. The reactor recovered 85.0% of the phosphorus in the influent of the reactor, which was 62.0% of the phosphorus in the urine excreted into the toilet. It was considered that most of the recovered phosphorus in the reactor was in the form of struvite.
