This study examined the disinfection efficiency of free chlorine and monochloramine for improve water quality, but if sources of controlling biofilm organisms in a model pipe system. The composition of the pipe material microbial contamination (e.g., sediment, was found to be a major influence on disinfection efficiency. Bacteria grown on galvanized, tubercles, flocculated materials) are not copper, or PVC pipe surfaces were readily inactivated by a 1-mg/L residual of free chlorine or eliminated, deterioration will soon monochloramine. Biofilms grown on iron pipes treated with free chlorine doses as high as 4 recur.lO In practice, it is difficult to mg/L (3-mg/L residual) for two weeks did not show significant changes in viability, but if effectively apply these procedures to treated with 4 mg/L of monochloramine for two weeks, these biofilms exhibited a more than transmission mains and trunk lines 3-log die-off. Accumulation of corrosion products on iron pipes was found to interfere with without extreme effort, high costs, and free chlorine disinfection.

This article examines the application of biological treatment strategies to current problems of the water industry. The studies focused on the production of biologically stable water, increased disinfectant stability, and reduced formation of disinfection by‐products. Results show that biological processes can meet the practical as well as the regulatory requirements of the industry.

Previous research has shown a relationship between corrosion of an iron pipe and the protection of biofilm bacteria from disinfection. It is believed that the corrosion product reacts with chlorine disinfectants and prevents the biocide from penetrating the biofilm layer and inactivating the attached bacteria. The results of the current study show that even low levels of corrosion, i.e., <1 mpy, could interfere with free chlorine disinfection. High corrosion rates affected monochloramine disinfection. The research also suggested that the type of corrosion influences the efficiency of disinfection of the biofilm. Increases in the ratio of chloride and sulfate to bicarbonate (the Larson index) have been shown to be associated with pitting corrosion, which appears to interfere with disinfection more than general corrosion. Multiple linear regression models were able to predict approximately 75 percent of the variation in biofilm inactivation. Provided that low corrosion rates and Larson indexes are achieved, no one corrosion inhibitor is preferred over another to control biofilm bacteria. The authors recommend that water utilities monitor and control corrosion rates and Larson indexes to levels as low as feasible.

No abstract

A survey of 94 water companies and districts was conducted in early 1988 to determine lead levels at customer taps and to evaluate the factors that influence these levels. The results of the survey indicate that lead‐based solder is the most significant source of lead at the tap. In addition, brass faucets were found to contribute substantially to the lead in the first‐draw samples. Although water quality and site characteristics cannot be used to predict lead levels, certain factors are associated with higher lead concentrations. Other than the presence of corrosion inhibitors, pH was the only water quality factor that appeared to influence lead levels at the tap. Site factors were also important, with plumbing age being the most significant.

Thermal regenerations were conducted on a granular activated carbon (GAC) that had become exhausted (spent) in a water treatment plant where it had been in service nearly four years. This GAC contained 2 percent calcium. With this field‐loaded calcium intact, proper regeneration restored the spent GAC to the same pore structure and surface area that was exhibited by several virgin GACs. When calcium appeared inside the spent GAC, it always caused micropores to be converted to small mesopores during thermal oxidation. In contrast, if the calcium was leached out of the spent GAC with acid, thermal oxidation increased only the micropore volume. Several regeneration variables were tested, including pyrolysis temperature (650–950°C), oxidation temperature (650–950°C), oxidant gas (steam and CO2), oxidant flow rate, and oxidant extent. All regenerated products of the spent GAC that had been taken to the same targeted apparent density displayed the same surface area and pore structure except those regenerated at low temperatures (650–750°C) with both steam and CO2 together: these produced carbons with lower volumes of small pores and lower surface areas.

The design, operation, and performance of granular activated carbon (GAC) filter‐adsorbers were documented and potential problems were identified by means of a survey of operating plants and a review of the literature. It was found that GAC as a total or partial replacement for sand is as effective as conventional filtration media for removing turbidity, provided an appropriate medium size has been selected. In addition, filter‐adsorbers can consistently eliminate tastes and odors from water supplies for extended periods of time. Sand‐replacement filter‐adsorbers, however, do not function well for removing less strongly adsorbed compounds such as trihalomethanes, volatile organics, and fractions of total organic carbon. More research is needed to determine whether microbial growth in filter‐adsorbers is beneficial or detrimental.

Properly treated, blended, and monitored waste streams can be recycled through the water treatment process, thus relieving disposal problems and conserving water. Waste streams recycled to the influent of a water treatment plant typically contain contaminants at concentrations that are of concern. These contaminants may include Giardia and Cryptosporidium, trihalomethanes, manganese, and assimilable organic carbon. This research shows that proper management—treatment, equalization, and monitoring—of the waste streams can render them suitable for recycling in many situations.