Department of Civil and Environmental Engineering, University of Nevada, MS-0258, Reno, NV 89557-0258, USA; Truckee Meadows Water Authority, 1355 Capital Blvd, Reno, NV 89502, USA.
EOA, Inc., Oakland, CA, USA.
Sci Total Environ. 2022 Feb 10;807(Pt 3):151053. doi: 10.1016/j.scitotenv.2021.151053. Epub 2021 Oct 18.
The State of Nevada, USA Administrative Code requires a 12-log enteric virus reduction/inactivation, 10-log Giardia cyst reduction, and 10-log Cryptosporidium oocyst reduction for Category A+ reclaimed water suitable for indirect potable reuse (IPR) based on raw wastewater to potable reuse water. Accurately demonstrating log reduction values (LRVs) through secondary biological treatment prior to an advanced water treatment train enables redundancy and resiliency for IPR projects while maintaining a high level of public confidence. LRVs for Cryptosporidium and Giardia resulting from secondary biological treatment are not fully established due to a wide range of performance variabilities resulting from different types of secondary biological treatment processes employed in water reclamation. A one-year investigation of two full-scale northern Nevada (e.g. ≤4 mgd; 1.5 × 10 L/day) water reclamation facilities (WRFs) was conducted to monitor Cryptosporidium oocysts and Giardia cysts in untreated wastewater and secondary effluent. This study aimed at establishing secondary treatment LRVs, monitor WRF performance and attempted to correlate performance to protozoan reduction. California's IPR regulations, in which Nevada IPR regulations were modeled after, were based on a maximum concentration of 5-logs (cysts/L) of Giardia and 4-logs (oocysts/L) of Cryptosporidium. The recovery-corrected Giardia and Cryptosporidium concentrations measured in untreated influent (20 samples each at each WRF) were below 5-log cysts/L at the 99th percentile (maximum 4.4-log cysts/L) and 4-log oocysts/L (maximum 2.7 log oocysts/L), respectively. Both secondary treatment WRFs produced secondary effluent that is consistently better than federal and the State of Nevada requirements and perform within an operating envelop for other secondary facilities. Given the results, it appears that a minimum conservative estimate for LRVs for well-operated secondary activated sludge treatment plants (at the 5th percentile) of 0.5 LRV credit for Cryptosporidium and 2.0 LRV for Giardia is warranted. These minimum LRVs are consistent with a conservative review of the available literature.
美国内华达州行政法规要求，对于 A+类再生水（适用于基于原废水的间接饮用水再利用（IPR）），需要进行 12 对数的肠道病毒减少/灭活、10 对数的贾第虫孢囊减少和 10 对数的隐孢子虫卵囊减少。在先进的水处理工艺之前，通过二级生物处理准确地证明对数减少值（LRV），可以为 IPR 项目提供冗余性和弹性，同时保持公众的高度信心。由于在水回收中使用的不同类型的二级生物处理工艺导致性能变化范围广泛，因此二级生物处理产生的隐孢子虫和贾第虫的 LRV 尚未完全确定。对两个位于内华达州北部的全规模（例如，≤4mgd；1.5×10L/天）水回收设施（WRF）进行了为期一年的调查，以监测未经处理的废水中的隐孢子虫卵囊和贾第虫孢囊以及二级出水。本研究旨在建立二级处理 LRV，监测 WRF 性能，并尝试将性能与原生动物减少相关联。内华达州的 IPR 法规是仿照加利福尼亚州的 IPR 法规制定的，规定贾第虫的最大浓度为 5 对数（孢囊/L），隐孢子虫的最大浓度为 4 对数（卵囊/L）。在每个 WRF 处对未经处理的进水（每个 WRF 处各有 20 个样本）进行了校正回收率的贾第虫和隐孢子虫浓度测量，在第 99 个百分位数（最大 4.4 对数孢囊/L）和 4 对数卵囊/L（最大 2.7 对数卵囊/L）以下。两个二级处理 WRF 产生的二级出水均始终优于联邦和内华达州的要求，并且在其他二级设施的运行范围内。鉴于这些结果，对于运行良好的二级活性污泥处理厂（在第 5 个百分位数），似乎可以保守地估计隐孢子虫的 LRV 为 0.5LRV 信用，贾第虫的 LRV 为 2.0LRV。这些最低 LRV 与对现有文献的保守审查一致。
