Removal of Emerging Contaminants in Drinking Water Treatment

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Biofiltration is a drinking water treatment process which relies on naturally occurring microorganisms that have formed a biofilm on filter media. Biofilters have been shown to effectively remove a wide variety of compounds including micropollutants, taste and odor causing compounds and inorganics.*******N-nitrosodimethylamine (NDMA) is a disinfection by-product (DBP) that is suspected of carcinogenic activity. A growing number of drinking water treatment plants that use chloramines for secondary disinfection have reported NDMA in finished water due to the reaction of chloramines with small nitrogen-containing molecules such as dimethylamine (DMA) that serve as NDMA precursors. With respect to NDMA precursors, it is hypothesized that biofiltration is able to reduce some of the precursors, but may contribute others. These may include bacterial and soluble microbial products (SMP) which are comprised of compounds released from the biofilm as waste, or sheared off of the media. It is expected that the release of biofilter derived precursors is dependent on biofilter operational conditions including filter design and pre-treatment.*******Many different NDMA precursors have been shown to be derived from anthropogenic sources. Of particular interest are pharmaceutically active compounds that have high molar conversions to NDMA upon chloramination. A number of PhACs that readily convert to NDMA are found in wastewater, but their presence in drinking water plant influents will depend on potential wastewater impacts. Pilot testing will concurrently evaluate the impact of flowrate, media type and pre-treatment for the removal of precursor compounds by biofiltration. Pilot- and full-scale studies will evaluate a range of EBCT ranging from 5 to 30 minutes to examine the formation of biomass and the removal or formation of NDMA precursors. Although it is expected that longer EBCT will provide better removals of NDMA precursors, and biodegradable organics, it is unclear whether increased biomass density will result in the formation of NDMA precursors in the filter effluent. Careful consideration may be required to optimize the removal of organics without generating excess biomass which may result in increased NDMA precursor formation.*******Confirmation of NDMA precursor removal efficiencies will provide valuable information to other researchers. This will also be of importance to utilities that already have biofiltration as well as those contemplating implementation in lieu of conventional granular filters. In addition, benefits will be realized by consultants who are involved in the water treatment industry, membrane and carbon producers, and regulatory setting agencies such as Health Canada and provincial environment ministries.******