Comparison between complete and partial recovery of N and P from stale human urine with MAP crystallization

Abstract

To provide an option of magnesium ammonium phosphate (MAP) crystallization for different recovery objective and treatment aim of separated stale human urine, five lab-scale tests were conducted, among which two of them acted as complete N and P recovery and three of them as partial N and complete P recovery, respectively. The results showed the recovery efficiencies of PO43–-P were more than 85% when the molar ratio of Mg/N/P was above the needed stoichiometric proportion for MAP precipitation. Although higher recovery efficiencies of NH4+-N and PO43–-P could be obtained by adding more phosphate and magnesium salts during MAP precipitation, there existed disadvantages such as inconvenient operation, hard to be put into practice, high operation cost, etc. Thus it was not recommended to completely recover NH4+-N and PO43–-P simultaneously if there were no wastes containing high phosphorus on hand. All harvested precipitates were identified as nearly pure struvite with the presence of trace elements of K, Na, Ni, Mn, and Ca.