Disinfection Interference in Wastewaters by Natural Organic Nitrogen Compounds

A wastewater treatment plant in Hampton Roads, VA, that handles considerable quantities of brewery waste reported periodic problems achieving proper disinfection. Because brewery waste contains high concentrations of organic nitrogen compounds, it was suspected that these compounds were responsible for disinfection interferences. Brewery effluent was mixed with different wastewaters to form mixtures with varying chemical characteristics. Each was chlorinated to the same level, and the fecal coliform levels were measured over the following hour. Mixtures that contained high ratios of total organic nitrogen to ammonia (TON/NH3 ≥ 1.5) were poorly disinfected by aqueous chlorine, and the rate with which they were disinfected tended to decrease with increasing TON/NH3 ratios. Samples with high TON/NH3 ratios were generally disinfected with preformed monochloramine at much faster rates than similar samples disinfected with aqueous chlorine. The formation of poorly bactericidal organic chloramines was implicated.