Removal of Emerging Contaminants in Drinking Water Treatment

生物过滤是一种饮用水处理工艺，依靠自然产生的微生物在滤料上形成生物膜。生物过滤器已被证明可以有效地去除各种化合物，包括引起化合物和无机物的微污染物、味道和气味。 N-亚硝基二甲胺(NDMA)是一种被怀疑具有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，由于氯胺与用作NDMA前体的含氮小分子(如二甲胺)发生反应，成品水中存在NDMA。关于NDMA前体，假设生物过滤能够减少一些前体，但可能会贡献其他前体。这些可能包括细菌和可溶性微生物产品(SMP)，这些产品由作为废物从生物膜中释放出来的化合物组成，或者从介质中剪切出来。预计生物滤池衍生前体的释放取决于生物滤池的运行条件，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。特别令人感兴趣的是具有药用活性的化合物，它们在氯胺化后具有高的摩尔转化率来转化为NDMA。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。中试测试将同时评估流量、介质类型和预处理对生物过滤去除前体化合物的影响。试点和全面研究将评估从5到30分钟不等的EBCT，以检查生物量的形成和NDMA前体的去除或形成。尽管预计较长的EBCT将更好地去除NDMA前体和可生物降解的有机物，但尚不清楚生物质密度的增加是否会导致过滤出水中NDMA前体的形成。可能需要认真考虑，在不产生可能导致NDMA前体形成的过剩生物量的情况下，优化有机物的去除。 对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。这对已经有生物过滤的公用事业公司以及那些考虑用来代替传统颗粒过滤器的公用事业公司也很重要。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制定机构将实现收益。

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.