Impacts of ozonation and membrane filtration on drinking water biostability and the effects of sample storage on the assimilable organic carbon (AOC) bioassay

One of the measures of drinking water biostability is the Assimilable Organic Carbon (AOC) bioassay. Holding experiments indicated that AOC values were affected by storage of samples over a 7-day period (65% increase). For samples obtained from the Floridan aquifer in two separate distribution systems, it was found that the allowable period of storage of samples for AOC analysis was 2 days when pasteurization was performed at 70°C for 30 minutes, up to 7 days of storage for a pasteurization of 72°C for 30 minutes followed by an ice bath for 30 minutes.; To determine the short and long-term effects of the introduction of ozonation as a treatment process on a drinking water treatment plant that previously used chlorination alone, a two-year study of biostability was performed. Ozonation resulted in very significant increases (over 100%) in AOC as compared to chlorination alone. This effect resulted in a similar increase in distribution system Heterotrophic Plate Counts (HPC) even though chlorine residuals did not change.; To monitor the effectiveness of nanofiltration (NF) as a water treatment process for the removal of AOC and Biodegradable Dissolved Organic Carbon (BDOC), a full-scale water treatment plant was investigated for one year. NF was effective in the reduction of BDOC (96% removal) and Dissolved Organic Carbon (92% removal). It was also observed that a higher disinfectant residual was maintained in the NF distribution system compared to lime softened water from the same aquifer. In contrast to these improvements in water quality, the full-scale NF did not reject the major fraction of AOC.; The effect of raw water characteristics (pH, hardness and ionic strength) on AOC and BDOC removal via membrane filtration (i.e. reverse osmosis---RO---and nanofiltration) was determined in bench-scale studies. AOC removal was a function of membrane type (RO vs. NF), hardness and ionic strength; and the relative removal was optimized at conditions of low hardness and low ionic strength. On the other hand, BDOC removal was a function of membrane type, pH, hardness, ionic strength and their interactions. Optimum relative removal was observed at conditions of high pH, low hardness and low ionic strength. RO membranes showed BDOC removal superior to NF membranes.