Abstract:The growing scarcity of potable water supplies is among the most important issues facing many cities, in particular those using single sources of water that are climate dependent. Consequently, urban centers are looking to alternative sources of water supply that can supplement variable rainfall and meet the demands of population growth. A diversified portfolio of water sources is required to ensure public health, as well as social, economical and environmental sustainability. One of the options considered is the augmentation of drinking water supplies with advanced treated recycled water. This paper aims to provide a state of the art review of water recycling for drinking purposes with emphasis on membrane treatment processes. An overview of significant indirect potable reuse projects is presented followed by a description of the epidemiological and toxicological studies evaluating any potential human health impacts. Finally, a summary of key operational measures to protect human health and the areas that require further research are discussed.

We investigated water quality at an advanced water reclamation plant and three conventional wastewater treatment plants using an "ecotoxicity toolbox" consisting of three complementary analyses (chemical analysis, in vitro bioanalysis and in situ biological monitoring), with a focus on endocrine disruption. The in vitro bioassays were chosen to provide an appropriately wide coverage of biological effects relevant to managed aquifer recharge and environmental discharge of treated wastewater, and included bioassays for bacterial toxicity (Microtox), genotoxicity (umuC), photosynthesis inhibition (Max-I-PAM) and endocrine effects (E-SCREEN and AR-CALUX). Chemical analysis of hormones and pesticides using LCMSMS was performed in parallel to correlate standard analytical methods with the in vitro assessment. For two plants with surface water discharge into open drains, further field work was carried out to examine in situ effects using mosquitofish (Gambusia holbrooki) as a bioindicator species for possible endocrine effects. The results show considerable cytotoxicity, phytotoxicity, estrogenicity and androgenicity in raw sewage, all of which were significantly reduced by conventional wastewater treatment. No biological response was detected to RO water, suggesting that reverse osmosis is a significant barrier to biologically active compounds. Chemical analysis and in situ monitoring revealed trends consistent with the in vitro results: chemical analysis confirmed the removal trends observed by the bioanalytical tools, and in situ sampling did not reveal any evidence of endocrine disruption specifically due to discharge of treated wastewater (although other sources may be present). Biomarkers of exposure (in vitro) and effect (in vivo or in situ) are complementary and together provide information with a high level of ecological relevance. This study illustrates the utility of combining multiple lines of evidence in the assessment of water quality.

The quality and safety of reverse osmosis (RO)-treated secondary wastewater, for indirect potable re-use, was assessed using a dataset of 375 chemicals measured in RO-treated wastewater. A screening health risk assessment indicated that four N-nitrosamines were of potential concern, although median concentrations of these chemicals were always below health values. The most frequently detected chemicals in RO-treated water were disinfection by-products, volatile organic compounds, metals and complexing agents, in contrast to many monitoring programs that focus on pharmaceuticals, personal care products and hormones. Frequent detections in RO-treated wastewater were most related to high concentrations in secondary wastewater, relative to limit of reporting, and the potential for chemicals to form or be added during the treatment process, rather than poor rejection by RO membranes. Between 3.7 and 10.7 μg/L of dissolved organic carbon (DOC) in RO permeate could be attributed from chemicals detected on at least one occasion, with the majority of this total attributed to chemicals detected in less than 25% of samples. While chemicals below detection may contribute a significant component of DOC, it is likely that natural organic matter and soluble microbial products still contribute the majority of DOC to RO permeate. 2A high degree of safety is demonstrated for the use of RO-treated wastewater as an indirect source of potable water.

A suite of 34 disinfection by-products (DBPs), including 8 halomethanes, 9 haloacetic acids, 6 haloacetonitriles, 6 haloaldehydes, 4 haloketones and the halonitromethane chloropicrin, were monitored in two microfiltration (MF) and reverse osmosis (RO) treatment plants as part of a larger study of chemical removal by MF/RO treatment for water recycling purposes. Both DBP detection frequency and concentration increased during treatment, and this was attributed to a chloramination step used to minimize RO membrane fouling. The degree of DBP formation was particularly related to plant residence time, with DBPs falling into two distinct groups; the first group in which DBP concentration increased with increasing residence time (e.g. chloroform and bromochloroacetaldehyde) and a second group in which increased residence time did not affect the concentration (e.g. dichloroacetic acid and 1,1-dichloropropanone). These results indicate that MF/RO plant design and wastewater quality are both important factors in minimising DBP formation within MF/RO treatment. RO rejection was influenced by several chemical-specific properties, including pKa, log Kow and DBP class. Rejection of haloacetic acids, present as charged molecules, was consistently better than 90% and did not alter with log Kow. For all other DBPs, present as neutral molecules, rejection was much more variable, and decreased with decreasing log Kow, although the effect of MW and log Kow on rejection could not be separated. The DBP formation described in this study lead to variable estimations of DBP removal by RO and thus it is recommended that DBPs are used as indicators of RO removal efficiency with caution, and only after DBP formation within RO treatment has been studied.

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