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During drinking water disinfection, natural organic matter (NOM) combines with the disinfectantto produce disinfection byproducts (DBPs), including haloacetic acids (HAAs) andtrihalomethanes (THMs). Considerable evidence is emerging that HAAs are biodegradablewithin biofilters in drinking water treatment plants. Because HAAs and THMs are formedsimultaneously during drinking water chlorination, approaches for biodegrading both classes ofDBPs must be developed before biological treatment can be considered a realistic option fordestroying a reasonable portion of the DBPs formed during prechlorination. Because of thegreater difficulty in biodegrading THMs, the development of a THM biotreatment process is thelimiting factor in implementing biological treatment for DBP control. This research providesfundamental information on the feasibility and development of a new biological treatmentprocess for the destruction of THMs formed in drinking water treatment plants.The treatment process is based on THM cometabolism by nitrifying bacteria growing onammonia (NH3) in multimedia filters. Cometabolism can be defined as the fortuitousbiodegradation of a target chemical (i.e., the cometabolite) through reactions catalyzed by one ormore non-specific microbial enzymes. This research is unique in that almost no work has beendone on biological treatment processes for THMs. The process may be especially useful forutilities that prechlorinate for some period prior to ammonia addition to form chloramines. Bycombining the reactive surface properties of granular activated carbon (GAC) for chloraminedestruction with nitrifying bacteria that grow in biofilters without the addition of organic carbonto the water, an innovative treatment process will be developed that allows for upstreamdisinfection, 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 formedwithin the treatment plant, thereby resulting in a lower concentration of THMs entering thedistribution system.The basic premise for this THM cometabolism treatment process derives from research notspecifically directed toward drinking water treatment (i.e., soil and aquifer remediation research).Therefore, much basic research is needed to document process performance under drinking watertreatment conditions and to assess the feasibility of the proposed process. The key question iswhether nitrifying bacteria growing in granular media beds can reliably cometabolize THMs at asufficient 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 pureculture Nitrosomonas europaea, an enriched culture of Nitrosomonas oligotropha from Dr.Daniel Noguera's laboratory at the University of Wisconsin at Madison, and a mixed culturefrom Lake Austin in Austin, Texas. In addition to these kinetic experiments, biofilterexperiments were initiated to demonstrate process performance. Includes 9 references, tables, figures.

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Edition: Vol. - No. Published: 11/02/2003 Number of Pages: 18File Size: 1 file , 390 KB