Impact of Biological Nitrogen Removal on Chlorination at New York City Water Pollution Control Plants

Abstract

The Nitrogen Control Feasibility Plan (NCFP) has identified step-feed biological nitrogen removal for meeting effluent total nitrogen concentrations < 9 mg-N/L and < 4 mg-N/L at several New York City Water Pollution Control Plants (NYC WPCPs). Under current non-BNR mode operating conditions, the NYC WPCPs rely on chlorination using sodium hypochlorite. Sodium hypochlorite doses are controlled based on the effluent total residual chlorine concentrations and the wastewater flow rate. Given the anticipated shift to BNR operation, we investigated the effect of BNR associated effluent nitrogen species concentrations on the efficacy of disinfection and chlorine dosage required to achieve a given effluent fecal coliform concentration and total chlorine residual concentration. Specifically, we examined the effect of low to intermediate NH 4 + -N concentrations; resulting from nitrification, NO 2 --N concentrations; resulting from incomplete nitrification or denitrification, the relative proportion of NH 4 + -N to unbiodegradable organic-N, suspended solids, all of which may be present in the reactor effluent on disinfection via chlorination. In addition, issues such as formation of toxic disinfection byproducts were addressed in light of the New York State Department of Environmental Conservation's (NYSDEC) promulgation of a total residual chlorine standard, which has identified chlorinated effluent as acutely toxic and an impending reduction in the existing total residual chlorine permit limits. Further, the effect of increased total suspended solids concentrations (poor settling characteristics of BNR sludge due to higher filament abundance on pathogen kill were also evaluated.

Disinfection and Antimicrobial Processes

“…The effect of biological nutrient removal on chlorination was studied. Effluent nitrogen species and their effect on chlorine dosage and total chlorine concentration were evaluated by examining nitrogen species concentrations resulting from nitrification/denitrification (Chandran et al, 2004). Ozdemir and Dursun (2004) collected wastewater samples from the beginning of a discharge channel in Turkey to investigate THM removal.…”