The increasing use of reclaimed water for irrigation in areas lacking access to advanced wastewater treatment and reclaimed water distribution systems calls for an examination of irrigation-site-based treatment technologies that can improve the quality of this alternative water source. To address this need, we investigated the impact of zero-valent iron (ZVI)-sand filtration on the bacterial community structure and functional potential of conventionally treated reclaimed water utilized in downstream applications. Over a 2-month period, reclaimed water was collected from a tertiary wastewater treatment plant in the Mid-Atlantic, U.S. and trucked to our greenhouse facility. The water was stored in rain barrels and then filtered through one ZVI-sand filter every 5 days. Filtrate was then subjected to enumeration, phylotyping, shiga toxin screening, and antimicrobial susceptibility testing of Escherichia coli. Aliquots of filtrate were also DNA extracted, and purified DNA was subjected to 16S rRNA gene sequencing and metagenomic shotgun sequencing. The genera Dechloromonas, Desulfotomaculum, Leptonema, and Thermomonas, which contain denitrifying and sulfate reducing species, commonly used in bioremediation, and known to increase the inherent reactivity of ZVI, were significantly more relatively abundant in ZVI-sand filtered reclaimed water compared to reclaimed water. The concentration of E. coli in ZVI-sand filtered reclaimed water was significantly lower compared to that of reclaimed water, and cefoxitin- and tetracycline-resistant E. coli were undetectable after ZVI-sand filtration. ZVI-sand filtration reduced the occurrence of human as well as plant pathogenic genera (Aeromonas, Mycobacterium, Shewanella, Acidovorax, Agrobacterium, and Clavibacter) but increased the proportion of Azospira, a nitrogen fixing bacterial genera, in the microbial community. Our exploratory functional analysis showed a modest non-significant increase in the proportion of open reading frames for genes associated with iron uptake, oxidative stress, as well as defense and repair mechanisms after ZVI-sand filtration. These data indicate an iron rich environment in the filter causing an oxidative stress response by the bacterial community present in the reclaimed water. Our findings demonstrate that ZVI-sand filtration effectively filters conventionally treated reclaimed water. Longer-term, field-based studies are needed to evaluate the effectiveness of the filter in agricultural settings and inform the development of future agricultural water reuse regulations.

中文翻译：

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零价铁砂过滤可减少人类和植物病原菌，同时增加再生水中促进植物生长的细菌

在无法获得高级废水处理和再生水分配系统的地区越来越多地使用再生水进行灌溉，这就要求对基于灌溉地点的处理技术进行检查，以提高这种替代水源的质量。为了满足这一需求，我们研究了零价铁 (ZVI) 砂过滤对下游应用中使用的常规处理再生水的细菌群落结构和功能潜力的影响。在 2 个月的时间里，从美国中大西洋的三级污水处理厂收集再生水，并用卡车运到我们的温室设施。水储存在雨桶中，然后每 5 天通过一个 ZVI 砂滤器过滤一次。然后对滤液进行计数、系统发育、志贺毒素筛选、和大肠杆菌的药敏试验。滤液的等分试样也提取 DNA，纯化的 DNA 进行 16S rRNA 基因测序和宏基因组鸟枪测序。Dechloromonas、Desulfotomaculum、Leptonema 和 Thermomonas 属含有反硝化和硫酸盐还原物种，常用于生物修复，并且已知会增加 ZVI 的固有反应性，与再生水相比，在 ZVI 砂过滤再生水中的含量明显相对丰富. 与再生水相比，ZVI 砂过滤再生水中的大肠杆菌浓度显着降低，并且在 ZVI 砂过滤后检测不到耐头孢西丁和四环素的大肠杆菌。ZVI 砂过滤减少了人类和植物病原菌属（气单胞菌属、分枝杆菌、希瓦氏菌、嗜酸菌、农杆菌和棒状杆菌），但增加了微生物群落中固氮细菌属固氮螺的比例。我们的探索性功能分析显示，在 ZVI 砂过滤后，与铁吸收、氧化应激以及防御和修复机制相关的基因的开放阅读框比例适度增加，但不显着。这些数据表明过滤器中富含铁的环境导致再生水中存在的细菌群落产生氧化应激反应。我们的研究结果表明，ZVI 砂过滤可有效过滤经过常规处理的再生水。长期，