Phosphorus recovery from urine by adding difference sources of magnesium ion, applying for rural, coastal and island areas in Vietnam

In coastal areas and islands, farmlands often lack of nutrients. This research assessed the precipitation of phosphorus presenting in urine in the form of struvite of magnesium ammonium phosphate (MAP) by adding of supplement of  Mg2+ ion from MgCl2 solution contained in seawater (Cat Ba island area). The urine and seawater have been mixed at different ratios. The results have shown [Mg]:[PO4] ratios ranging from 0.75 to 5.26 allowed the precipitation of more than 90% of the phosphorus in the urine. Seawater – to – urine ratios of 0.67/1, 1.3/1, 3.2/1, 5/1, 7/1 and 9/1 in volume would give phosphorus recovery efficiency of 99%, 92%, 96%, 96%, 95% and 99%, respectively. Seawater in the studied area could be an appropriate Mg2+ ion source to produce MAP from urine diverting dry toilets. Recovered phosphorus can be used as slow releasing fertilize for farming. Keywords: MAP: phosphorus recovery; seawater; urine; struvite. Received 24 October 2018, Revised 23 December 2018, Accepted 29 January 2019