AWWA WQTC58991

During drinking water disinfection, natural organic matter (NOM) combines with the disinfectant to produce disinfection byproducts (DBPs), including haloacetic acids (HAAs) and trihalomethanes (THMs). Considerable evidence is emerging that HAAs are biodegradable within biofilters in drinking water treatment plants. Because HAAs and THMs are formed simultaneously during drinking water chlorination, approaches for biodegrading both classes of DBPs must be developed before biological treatment can be considered a realistic option for destroying a reasonable portion of the DBPs formed during prechlorination. Because of the greater difficulty in biodegrading THMs, the development of a THM biotreatment process is the limiting factor in implementing biological treatment for DBP control. This research provides fundamental information on the feasibility and development of a new biological treatment process for the destruction of 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. The current focus of the research is determination of THM degradation kinetics with the pure culture Nitrosomonas europaea, an enriched culture of Nitrosomonas oligotropha from Dr. Daniel Noguera's laboratory at the University of Wisconsin at Madison, and a mixed culture from Lake Austin in Austin, Texas. In addition to these kinetic experiments, biofilter experiments were initiated to demonstrate process performance. Includes 9 references, tables, figures.