Removal of Ammonia from a Biologically Treated Pesticide Wastewater by Struvite Precipitation

The aim of this study was to investigate ammonia removal from the effluent of a full-scale biofilm reactor treating pesticide wastewater through the formation of struvite (MgNH4PO4 center dot 6H(2)O). The requirement of magnesium and phosphate ions for precipitation was met by adding MgO and Na2HPO4. Different NH4+:Mg2+:PO43- molar ratios were tested in batch reactors to optimize the precipitation conditions. Ammonia was reduced to 25 mg/L from an initial concentration of 210 mg/L at the highest ratio tested (1:1.2:1.3), equating to 88% removal. However, the extent of ammonia removal was only slightly affected when the N:Mg ratio was reduced from 1:1.2 to 1:0.6; dropping to 83% from 88% on a percentage basis. Struvite precipitation can be easily incorporated within the existing post-treatment section of the full-scale plant, providing the pesticide manufacturing facility with a reliable backup process for its nitrification system.