KWR Watercycle Research Institute, Groningenhaven 7, 3433 PE, Nieuwegein, The Netherlands.
National Institute for Public Health and the Environment, Bilthoven, The Netherlands; Department of Earth Sciences, University of Utrecht, Utrecht, The Netherlands.
Water Res. 2018 Aug 1;139:158-167. doi: 10.1016/j.watres.2018.03.054. Epub 2018 Mar 24.
Soil passage of (pretreated) surface water to remove pathogenic microorganisms is a highly efficient process under oxic conditions, reducing microorganism concentrations about 8 log within tens of meters. However, under anoxic conditions, it has been shown that removal of microorganisms can be limited very much. Setback distances for adequate protection of natural groundwater may, therefore, be too short if anoxic conditions apply. Because removal of microorganisms under suboxic conditions is unknown, this research investigated removal of bacteriophage MS2 and PRD1 by soil passage under suboxic conditions at field scale. At the field location (dune area), one injection well and six monitoring wells were installed at different depths along three suboxic flow lines, where oxygen concentrations ranged from 0.4 to 1.7 mg/l and nitrate concentrations ranged from 13 to 16 mg/L. PRD1 and MS2 were injected directly at the corresponding depths and their removal in each flow line was determined. The highest bacteriophage removal was observed in the top layer, with about 9 log removal of MS2, and 7 log removal of PRD1 after 16 meters of aquifer transport. Less removal was observed at 12 m below surface, probably due to a higher groundwater velocity in this coarser grained layer. MS2 was removed more effectively than PRD1 under all conditions. Due to short travel times, inactivation of the phages was limited and the reported log removal was mainly associated with attachment of phages to the aquifer matrix. This study shows that attachment of MS2 and PRD1 is similar for oxic and suboxic sandy aquifers, and, therefore, setback distances used for sandy aquifers under oxic and suboxic conditions provide a similar level of safety. Sticking efficiency and the attachment rate coefficient, as measures for virus attachment, were evaluated as a function of the physico-chemical conditions.
预处理地表水在有氧条件下通过土壤通道去除致病微生物是一种非常有效的过程，可在几十米的距离内将微生物浓度降低约 8 个对数级。然而，在缺氧条件下，已经表明微生物的去除可能会受到很大限制。如果存在缺氧条件，那么为自然地下水提供充分保护的后退距离可能会太短。由于亚缺氧条件下微生物的去除情况未知，因此本研究调查了在野外规模的亚缺氧条件下通过土壤通道去除噬菌体 MS2 和 PRD1 的情况。在该野外位置（沙丘区），在三条亚缺氧流线上的不同深度安装了一口注入井和六口监测井，其中氧气浓度范围为 0.4 至 1.7mg/L，硝酸盐浓度范围为 13 至 16mg/L。直接将 PRD1 和 MS2 注入到相应的深度，并确定在每条流线上的去除情况。在最上层观察到最高的噬菌体去除率，MS2 的去除率约为 9 个对数级，PRD1 的去除率约为 7 个对数级，在含水层输送 16 米后。在地表以下 12 米处的去除率较低，这可能是由于该较粗粒层中的地下水速度较高所致。在所有条件下，MS2 的去除效果均优于 PRD1。由于较短的传输时间，噬菌体的失活受到限制，报道的对数去除主要与噬菌体附着在含水层基质上有关。本研究表明，在有氧和亚缺氧砂质含水层中，MS2 和 PRD1 的附着相似，因此，在有氧和亚缺氧条件下用于砂质含水层的后退距离提供了相似的安全水平。作为病毒附着的度量，附着效率和附着速率系数被评估为理化条件的函数。
