AWWA JAW64227

Biofilters seeded with mixed-culture nitrifiers from Lake Austin, Texas, and fed nutrient and Lake Austin water biodegraded the four trihalomethanes (THMs) commonly found in treated drinking water - bromoform, chloroform, dibromochloromethane, and dichlorobromomethane. THMs were degraded by cometabolism, and degradation increased with increased THM bromine substitution and increased total ammonia-nitrogen biodegradation. Overall, these experiments resulted in sustained THM removals ranging from 10 to 60% for varying operating conditions. Three operational issues were also studied: THM product toxicity, nutrient limitations, and monochloramine inhibition of ammonia and THM degradation. The cometabolism stability index represents a simple and useful parameter for evaluating the likelihood of product toxicity problems in biofilter operation. Nutrient limitations (e.g., iron and copper) may exist for natural water sources, and supplemental nutrients may be needed to achieve maximum THM degradation rates. Influent monochloramine concentrations of 1 mg/L (or less) as Cl₂ appear to be a good target for stable operation of developed biofilm. Includes 34 references, tables, figures.