Removal of Emerging Contaminants in Drinking Water Treatment

生物过滤是一种饮用水处理工艺，它依赖于在过滤介质上形成生物膜的天然微生物。生物过滤器已被证明可以有效地去除各种各样的化合物，包括微污染物，味道和气味引起的化合物和无机物。 N-亚硝基二甲胺（NDMA）是一种疑似致癌活性的消毒副产物（DBP）。越来越多使用氯胺进行二次消毒的饮用水处理厂报告称，由于氯胺与作为NDMA前体的二甲胺（DMA）等含氮小分子反应，成品水中含有NDMA。关于NDMA前体，假设生物过滤能够减少一些前体，但可能有助于其他前体。这些可以包括细菌和可溶性微生物产物（SMP），其由作为废物从生物膜释放的化合物组成，或从培养基上剪切下来。预计生物过滤器衍生前体的释放取决于生物过滤器的操作条件，包括过滤器设计和预处理。 许多不同的NDMA前体已被证明来自人为来源。特别感兴趣的是在氯胺化时具有高摩尔转化率的药物活性化合物。在废水中发现了许多容易转化为NDMA的PhAC，但它们在饮用水厂进水中的存在将取决于潜在的废水影响。中试将同时评估流速、介质类型和预处理对生物过滤去除前体化合物的影响。中试和全面研究将评估5至30分钟的EBCT范围，以检查生物质的形成和NDMA前体的去除或形成。尽管预计较长的EBCT将提供更好的NDMA前体和可生物降解的有机物的去除，但尚不清楚增加的生物质密度是否会导致过滤器流出物中NDMA前体的形成。可能需要仔细考虑优化有机物的去除而不产生过量的生物质，这可能导致NDMA前体形成增加。 NDMA前体去除效率的确认将为其他研究人员提供有价值的信息。这对于已经具有生物过滤的公用事业以及那些考虑替代传统颗粒过滤器的公用事业也很重要。此外，参与水处理行业的顾问、膜和碳生产商以及加拿大卫生部和省级环境部等监管机构也将从中受益。

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.