Effects of treatment changes on chloramine demand and decay

摘要

The practical experiences gained at the East Bay Municipal Utility District (EBMUD) in California and factors from the literature affecting combined chlorine (chloramine) demand and decay were reviewed. The main goal was to emphasize the importance of a stable chloramine residual entering the distribution system to minimize system maintenance. The rate of chloramine loss was not constant but varied in EBMUD's system as a result of source water quality and water treatment changes. A high degree of total organic carbon removal by either granular activated carbon (GAC) adsorption or nanofiltration would be required to improve chloramine stability beyond that of conventionally coagulated and settled water. Ozonation with or without hydrogen peroxide contributed to an increased chloramine demand. Filtration of the ozonated water through biologically active GAC/sand filter media substantially increased chloramine demand. New filter media, either GAC or anthracite/sand, did not exhibit this negative effect on chloramine demand. Free chlorine or chlorine dioxide applied to the filter effluent prior to chloramine formation helped maintain a stable chloramine residual.