Nitrification occurred in two covered finished‐water reservoirs in Southern California following a change from free chlorine to chloramine disinfection. The proliferation of autotrophic ammonia‐oxidizing bacteria was suspected to be the cause. Adverse water quality effects caused by the nitrification episodes included a rapid decline in the total chlorine and total ammonia‐nitrogen residuals and elevated levels of nitrite and heterotrophic plate count bacteria. As a result, the reservoirs were taken out of service and breakpoint‐chlorinated. This article examines the conditions leading to the development of nitrification in reservoirs containing chloraminated water, along with the measures that can be used to control the process.
These two processes effectively remove MTBE but may also increase bromate. Initial pilot‐scale investigations demonstrated that both ozone alone and a combination of ozone and hydrogen peroxide (known as peroxone) can remove methyl tertiary butyl ether (MTBE) from water sources used by the Metropolitan Water District of Southern California. Under the tested conditions, peroxone more effectively removed MTBE than did ozone alone. In pilot tests, peroxone (here, 4 mg/L ozone and 1.3 mg/L hydrogen peroxide) removed an average of about 78 percent of the MTBE from water samples taken from the California State Water Project and the Colorado River. However, in peroxone‐treated samples from both water sources at ambient conditions, bromate was produced at concentrations above the maximum contaminant level of 10 μg/L for bromate in drinking water. A lower pH of 6.5 reduced bromate formation by about 20 percent in samples from both water sources, but it did not reduce the bromate concentration below 10 μg/L (the water sources contained about 0.1 mg/L bromide). Further optimization of the peroxone process may minimize bromate formation while providing acceptable MTBE removal and disinfection.
Bench‐scale experiments were conducted to determine the effectiveness of using pulsed‐ultraviolet (UV) irradiation and pulsed‐UV/hydrogen peroxide (H2O2) processes to destroy N‐nitrosodimethylamine (NDMA). The effects of various UV and H2O2 dosages and source waters, as well as nitrate (NO3–) and initial NDMA concentrations, were investigated as control parameters for both completely mixed batch reactor and continuously stirred tank reactor tests. The presence of compounds that interfere with UV light (e.g., NO3–) and the formation of total trihalomethanes after pulsed‐UV treatment were also studied. Pulsed‐UV technology was highly effective for destroying NDMA. The pseudo–first‐order rate constants were calculated to be in the range of 1.4 to 12.2 min–1. This technology offers other benefits (e.g., disinfection) and can be applied directly to drinking water treatment. However, potential concerns in pulsed‐UV photolysis of NDMA include (1) the formation of undesirable chemicals as reaction intermediates and (2) possible reformation/regeneration of NDMA after chlorination of pulsed‐UV–treated effluent. Pulsed‐UV with a small amount of H2O2 could be used to control the reaction by‐products and to inhibit the reformation of NDMA by using hydroxyl radicals generated during an advanced oxidation process. In contrast, pulsed‐UV with a larger amount of H2O2 could inhibit NDMA decay by direct photolysis.
More than 200 agricultural drains in the Sacramento River Delta contribute significant levels of trihalomethane (THM) precursors to California State Project water. It has been hypothesized that these drains, associated with crop irrigation involving highly organic peat soils, are probably responsible for the higher levels of dissolved organic carbon and THM formation potential in the California Aqueduct emanating from the delta in comparison with the principal freshwater tributaries entering the delta. The purpose of this study was to evaluate this hypothesis. It was found that the dissolved organic matter from drains is characterized by a higher molecular weight and greater THM reactivity than that found in delta tributaries.
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