CHLORAMINATION OF N/DN EFFLUENT MEETING THE AMMONIA,COLIFORM AND THM LIMITS

摘要

The Los Angeles County Sanitation Districts (the Districts) are converting several waterrnreclamation plants to nitrification/denitrification (N/DN) mode. Ammonia addition isrnnecessary to prevent breakpoint chlorination and formation of trihalomethanes (THMs), andrnthe dose needs to be kept to a minimum to comply with its own discharge limit. The ability tornregulate the ammonia concentration in an N/DN plant effluent is crucial in complying withrnthe stringent limits of ammonia, total coliform, and THMs.rnA research project was recently completed at the Districts to study chloramination of N/DNrneffluent. The findings of this study include (1) ammonia added to the secondary effluentrnchannel was well mixed hydraulically before chlorine addition; (2) the N/DN effluent exertedrnsignificant chlorine demand shortly after chlorine addition; (3) the Cl2:NH3-N ratio at thernbreakpoint of chlorination was found to be around 11, higher than the theoretical ratio of 7.6;rn(4) THMs formation dropped as the ammonia concentrations increased; (5) approximatelyrn20% of the added ammonia was lost during the chlorination process; and (6) split chlorinationrnhad insiginificant impacts on THMs formation and chlorine residuals when chloraminationrnwas applied. This study generated useful and practical information for chloramination ofrnN/DN effluent to meet stringent discharge requirements.