Treatment of organophosphate-contaminated wastewater by acidic hydrolysis and precipitation

Wastewater from commercial manufacture of organophosphate (OP) pesticide of O-methyl-O-(2-isopropyl salicylate) thiophosphorusyl amide contains large amounts of organophosphate, organic sulfides, COD and NH3-N. A treatment process including acidic hydrolysis and precipitation was explored in this paper. The effects of initial pH values, hydrolysis temperature and hydrolysis time on the removal of pollutants were investigated. The experimental results showed that, in the hydrolysis, with the decreasing initial pH value, the removal of OP, sulfide and COD rose whereas the NH3-N removal declined. Increased hydrolysis temperature and time favored the removal of all the pollutants. 15.0 wt% Ca(OH)2 was sufficient for the removal of inorganic phosphorus and residual NH3-N in the precipitation step. With this chemical process, the removal of total phosphorus (TP), organophosphate, sulfides and NH3-N exceeded 90%, and the removal of COD was about 60%. The BOD5/COD value was greatly improved from 0.05 to 0.3, and the bio-degradability of the wastewater was greatly improved. The NH3 generated in the process was absorbed with water and might be reused in the manufacture of the pesticide. The results showed that this comprehensive process is effective for the treatment of this typical unbio-degradable pesticide wastewater.