AWWA WQTC60732

This research provides fundamental information on the feasibility and development of a new biological treatment process for the destruction of trihalomethanes (THMs) formed in drinking water treatment plants. The treatment process is based on THM cometabolism by nitrifying bacteria growing on ammonia (NH₃) in multimedia filters. Cometabolism can be defined as the fortuitous biodegradation of a target chemical (i.e., the cometabolite) through reactions catalyzed by one or more non-specific microbial enzymes. This research is unique in that almost no work has been done on biological treatment processes for THMs. The process may be especially useful for utilities that prechlorinate for some period prior to ammonia addition to form chloramines. By combining the reactive surface properties of granular activated carbon (GAC) for chloramine destruction with nitrifying bacteria that grow in biofilters without the addition of organic carbon to the water, an innovative treatment process will be developed that allows for upstream disinfection, while at the same time protecting bacteria in the downstream process (i.e., filtration) from the disinfectant. With this protection, bacteria will be able to biodegrade THMs formed within the treatment plant, thereby resulting in a lower concentration of THMs entering the distribution system. The basic premise for this THM cometabolism treatment process derives from research not specifically directed toward drinking water treatment (i.e., soil and aquifer remediation research). Therefore, much basic research is needed to document process performance under drinking water treatment conditions and to assess the feasibility of the proposed process. The key question is whether nitrifying bacteria growing in granular media beds can reliably cometabolize THMs at a sufficient rate to make this process attractive to utilities that practice (or want to practice) prechlorination, especially those practicing prechlorination with subsequent chloramination. Previous batch kinetic experiments demonstrated that all four THMs could be degraded by both a pure culture, Nitrosomonas europaea, and mixed culture nitrifiers (Wahman et al. 2003). Based on these results, biofilter experiments were conducted with columns seeded with mixed culture nitrifiers from Lake Austin, Texas, receiving nutrient water in the feed. Includes 3 references, tables, figures.