Breakpoint Chlorination of Petroleum Refinery WWTP Effluent

Breakpoint chlorination followed by dechlorination was studied as a non-biological option to remove ammonia and nitrite from a California petroleum refinery wastewater treatment plant (WWTP) effluent before final discharge. Chlorination/dechlorination facilities could serve as a contingency should the existing biological WWTP be unable to manage the wasteloads expected when processing crude oil with elevated nitrogen levels.In the laboratory, breakpoint chlorination successfully oxidized ammonia and nitrite spiked into WWTP effluent samples. The chlorinated/dechlorinated effluent had no adverse impact on rainbow trout survival in a 96-hour flow-through bioassay. However, the feasibility of full-scale treatment is doubtful, as WWTPs in California often have to meet a total residual chlorine limit of 0.0 mg/L. Demonstrating compliance with a “zero” chlorine effluent limit using either on-line analyzers or grab samples is difficult. A more reliable means of demonstrating compliance involves measurement of a positive sulfite residual, which indicates that chlorine is not present.