Data from US distribution systems that chloraminate are evaluated as predictors of nitrification. Utilities in the United States that chloraminate were surveyed to evaluate the incidence of nitrification in distribution systems and determine whether nitrification can be predicted from basic system and water quality data. An estimated two thirds of medium and large US systems that chloraminate experience nitrification to some degree. About every fourth surveyed utility reported moderate to severe nitrification problems. In addition, every fourth utility did not know the extent of nitrification in its system. The incidence of nitrification was more frequent during summer or when the temperature was greater than 15°C (59°F); nevertheless, several sites sampled under cold water conditions—i.e., below 10°C (50°F)—also evidenced nitrification. No one water quality parameter by itself may be a good indicator of nitrification, but several important factors should be evaluated collectively—nitrite, nitrate, chloramine dosage and residual, ammonia, pH, heterotrophic bacterial counts, and dissolved oxygen.

his article continues the discussion presented by Wilczak et al 1 in the companion article on page 74. The primary objective of this research was to develop practical utility information regarding the occurrence and control of nitrification in drinking water systems using chloramines for secondary disinfection. Specific research goals were to • document nitrification control practices used by utilities,• develop a laboratory method to demonstrate nitrification response under various water quality and operational parameters, and• establish a recommended monitoring and control strategy.Of US water systems that chloraminate, an estimated two thirds experience some degree of nitrification in the distribution system. Measures utilities use to control nitrification were investigated through field sampling, evaluation of utility data, laboratory tests, and case studies of systems that have evaluated or attempted to control nitrification episodes. Effective control methods included instituting periodic breakpoint chlorination, reducing the available ammonia concentration, increasing chloramine residuals, cleaning the distribution system, and decreasing system detention time. Some control methods were superior for controlling a specific nitrification episode, whereas others showed more promise for reducing the long-term potential for nitrification occurrence. According to the authors, the most important steps utilities can take to control nitrification are to thoroughly understand their systems' chloramine chemistry and to establish an effective monitoring strategy.

Cationic treatment polymer, diallyldimethylammonium chloride (DADMAC), was the only significant source of N‐nitrosodimethylamine (NDMA) precursors in tested waters at the East Bay Municipal Utility District. NDMA concentrations increased with higher cationic polymer doses and longer chloramine contact times. Recycled filter backwash supernatant was a significant source of NDMA precursors, possibly because of residual cationic polymer. Higher NDMA levels were formed with pre‐ammoniation or simultaneous addition of chlorine (Cl2) and ammonia (NH3), whereas free Cl2 contact time prior to chloramination resulted in lower NDMA concentrations with less dependence on polymer dose. NH3, nitrite, and nitrate did not form NDMA with DADMAC; chloramine was necessary to form significant levels of NDMA. NDMA concentrations in the chloraminated distribution system decreased when the cationic polymer doses at two treatment plants were decreased. The lowest concentrations of NDMA were observed in the service areas that received water that was coagulated at low polymer doses and did not contain recycled filter backwash water.

The rate of sorption of copper(II) and lead(II) onto activated carbons Nuchar SA and Filtrasorb 400 was observed to occur rapidly at the outset, followed by a slow and prolonged sorption. This indicates that previous sorption studies conducted for short equilibration periods likely underestimated the actual capacity of activated carbon for heavy metals. Although copper and lead ions desorbed from the activated carbon surface rapidly, the rate of desorption of lead was slower, prevailing over several days. Sorption of copper and lead ions on Nuchar SA was found to be fully reversible.zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Water Environ. Res.,zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 65, 238 (1993).

FIGURE 1U US SL L t tr re ea at tm me en nt t p pl la an nt t s sc ch he em ma at ti ic c a an nd d o op pe er ra at ti io on na al l c co on nd di it ti io on ns s Rapid mix Flocculator and settler Chloraminated 6 mil gal (23 ML) clearwell Chloraminated 6 mil gal (23 ML) clearwell Chloraminated 6 mil gal (23 ML) clearwell Ozone contactor GAC/sand filters + surface wash Alum Polymer Aeration basin Anthracite/sand filters + air scour 3 mil gal (11 ML) baffled Cl 2 contactor USL reservoir O 2 (hypolimnetic oxygenation) Rapid mix Flocculator and settler Ozone contactor GAC/sand filters + surface wash Aeration basin