Applied Research and Development Center, Southern Nevada Water Authority, P.O. Box 99954, Las Vegas, NV, 89193, USA.
HDR Engineering Inc., 5426 Bay Center Drive, Suite 400, Tampa, FL, 33609-3444, USA.
Water Res. 2019 Jan 1;148:526-534. doi: 10.1016/j.watres.2018.10.085. Epub 2018 Oct 30.
The combination of biological growth and particle loading can adversely affect hydraulic performance in drinking water biofilters. In this study, upstream oxidant addition was used to distribute biologically-derived filter clogging in granular activated carbon (GAC) biofilters. Oxidant penetration was assessed during pilot-scale operation and backwashing of dual media (GAC/sand) and multimedia (GAC/anthracite/sand) biofilters. Influent chlorine (HOCl), monochloramine (NHCl), and hydrogen peroxide (HO) residuals were optimized to react with the GAC surface in the upper portion of the filter media bed (depth < 0.5 m) to attenuate biomass development. As the oxidant residual was quenched by surface-mediated reaction with the filter media, biomass growth was promoted deeper in the filter bed (depth > 0.5 m). The oxidant-induced effects on biomass and hydraulic performance were monitored through measurements of adenosine triphosphate (ATP) and head loss accumulation at different media depths. Addition of oxidants (e.g., 0.6 mg Cl/L HOCl) could decrease terminal head loss by 20% in dual media filters and 40% in multimedia filters. These hydraulic benefits were achieved without significantly affecting removal of assimilable organic carbon (AOC), total organic carbon (TOC), turbidity, and particle counts. Oxidant type, residual concentration, media type, media age, and media depth influenced the passage of oxidant residuals and distribution of filter biomass. When oxidants were added during backwashing, oxidant residual was quenched through the bed depth from a combination of reactions with GAC media and biofilm degradation. This attenuation of residual oxidant may prevent the oxidant residual from penetrating the entire bed depth, potentially compromising backwashing objectives.
生物生长和颗粒负载的结合会对饮用水生物滤池的水力性能产生不利影响。在本研究中，采用上游氧化剂添加的方法来分布颗粒活性炭（GAC）生物滤池中的生物衍生的滤池堵塞。在中试规模运行和双层（GAC/砂）和多层（GAC/无烟煤/砂）生物滤池反冲洗期间评估了氧化剂穿透情况。优化进水氯（HOCl）、一氯胺（NHCl）和过氧化氢（HO）残留量，使其与过滤介质床（深度<0.5m）的上部的 GAC 表面反应，以衰减生物量的发展。随着氧化剂残留被过滤介质表面介导的反应消耗，生物量在过滤床更深的地方（深度>0.5m）生长。通过测量不同介质深度的三磷酸腺苷（ATP）和水头损失积累，监测氧化剂对生物量和水力性能的影响。添加氧化剂（例如，0.6mg Cl/L HOCl）可以使双层介质过滤器的终端水头损失降低 20%，多层介质过滤器的水头损失降低 40%。这些水力效益的实现不会显著影响可同化有机碳（AOC）、总有机碳（TOC）、浊度和颗粒计数的去除。氧化剂类型、残留浓度、介质类型、介质年龄和介质深度影响氧化剂残留的穿透和过滤生物量的分布。当在反冲洗期间添加氧化剂时，氧化剂残留通过与 GAC 介质和生物膜降解的组合反应从床层深度耗散。这种氧化剂残留的衰减可能会阻止氧化剂残留穿透整个床层深度，从而影响反冲洗的目标。
