Phosphorus recovery from human urine and anaerobically treated wastewater through pH adjustment and chemical precipitation.

Increased population growth and food prices have resulted in more demand for fertilizers, especially phosphorus (P), to be used in agriculture and production of food crops. This research investigated the feasibility of P recovery from selected wastewaters in the form of precipitates only with pH adjustment. Human urine and effluent of an anaerobic digester treating a piggery's wastewater were employed to determine appropriate pH conditions for P recovery including solubility of the precipitates in an agricultural soil. From the laboratory experiments, the highest P recovery was found to be 106 mg per one litre of urine at pH 11. Due to its lower P content, the highest P recovery from one litre of the anaerobic digester effluent was 39 mg at pH 9. The X-ray diffraction analysis of the precipitates identified them to consist of struvite, syn-NH4MgPO4 6H2O, and other precipitate compounds consisting of CaCO3, NaCl and Mg3Al2(SiO4)3 and P contents of the precipitate samples were found to be 3-7%. When mixed with soils at a moisture content of 50%, the extents of P solubilized from the precipitate samples were in the range of 50-60%. Application of these experimental results to full-scale operation for P recovery is suggested.