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.

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The Williamsburg, Virginia, wastewater treatment plant (WWTP) has periodically experienced erratic disinfection and persistence of fecal coliform bacteria in the presence of apparently adequate levels of disinfectant in the effluent. Several reasons for disinfection problems were previously investigated. This paper describes the results of a study of two factors that could affect disinfection in this plant: (1) the potential for the development of disinfection-resistant fecal coliforms in the operation of this specific WWTP and (2) the nature of the wastewater matrix that this particular WWTP handles that could interfere with chlorine disinfection. The study suggested that the WWTP oxidation towers supported growth or recovery of fecal coliform bacteria. This bacterial subpopulation seemed to have increased resistance to routine chlorine disinfection. Inactivation rate constants calculated for periods between 15 and 45 minutes after chlorine addition were significantly lower for fecal coliforms originating from oxidation towers than for fecal coliforms from other sources. This is, to our knowledge, the first report of such conditions created by a treatment process. The study of the plant-specific matrix determined no statistically significant effects on disinfection. Water Environ. Res., 71, 277 (1999).

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