CHLORINE INACTIVATION KINETICS OF FECAL COLIFORM AND ESCHERICHIA COLI IN LOW AMMONIA EFFLUENTS - CONTROL STRATEGY FOR PROCESS OPTIMIZATION

摘要

Many wastewater treatment plants (WWTP) in the U.S. have been converted from aconventional activated sludge process to a Nitrification/Denitrification (NdeN) processto meet more stringent total nitrogen effluent permit requirements. Operationaldifficulties have been encountered by many of these NdeN plants during chlorinedisinfection. Because the chlorine disinfection process is sensitive to the levels ofammonia, nitrite, and organic nitrogen, these constituents should be taken intoaccount when evaluating the inactivation kinetics and chlorine dose control strategy.Typically only flow and/or chlorine residual are used to control chlorine dose rates.While this strategy is suitable for non-nitrifying plants, complications arise in NdeNplants where chlorine demands fluctuate drastically due to the effect in breakpointchemistry caused by changing effluent characteristics. Low and fluctuating effluentammonia levels cause the chlorine reactions to swing in and out of breakpoint. Inaddition, various side reactions occur that often offset the advantages of loweredammoniacal chlorine demand and free chlorine formation. To date, no kinetic modelsare available to describe microbial inactivation taking into account the effects ofnitrogen constituents.From the models, it was found that ammonia enhances the low ammonia effluentchlorine disinfection process whereas the nitrite and organic nitrogen have negativeinfluence on chlorine disinfection. A practical application of the developed kineticmodel is its integration into an automated chlorine dose control algorithm for lowammonia, secondary effluent. The algorithm would be capable of adjusting thechlorine dose setpoint based on variations in secondary effluent nitrogen speciesconcentrations measured at the chlorine contact basin influent point. Ammonia, nitrite,and organic nitrogen monitoring can be accomplished with in-line probes or UVabsorbancesystems which are successfully operated at many wastewater treatmentfacilities today.