Clemencia Rodriguez

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.

An assessment of potential health impacts of dioxin and dioxin-like compounds in recycled water for indirect potable reuse was conducted. Toxic equivalency factors (TEFs) for 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (PCBs) congeners have been developed by the World Health Organization to simplify the risk assessment of complex mixtures. Samples of secondary treated wastewater in Perth, Australia were examined pre-and post-tertiary treatment in one full-scale and one pilot water reclamation plant. Risk quotients (RQs) were estimated by expressing the middle-bound toxic equivalent (TEQ) and the upper-bound TEQ concentration in each sampling point as a function of the estimated health target value. The results indicate that reverse osmosis (RO) is able to reduce the concentration of PCDD, PCDF and dioxin-like PCBs and produce water of high quality (RQ after RO=0.15). No increased human health risk from dioxin and dioxin-like compounds is anticipated if highly treated recycled water is used to augment drinking water supplies in Perth. Recommendations for a verification monitoring program are offered.

Indirect potable reuse schemes are an important consideration in the sustainable management of scarce water resources. However, communities still hold real concerns about the potential health risks of micropullutants in recycled water entering their potable water supply. Microfiltration or ultrafiltration followed by reverse osmosis is currently the standard treatment technology for potable use of recycled water. Nevertheless, membranes are not 100% efficient in the removal of trace organic contaminants and the potential health risks of these micropullutants need to be assessed. The aim of this paper is to present a three-tiered approach for the preliminary assessment of micropullutants in recycled water. A risk quotient is calculated by comparing measured concentrations against benchmark values. Tier 1 corresponds to regulated chemicals; the maximum contaminant level in drinking water is used as benchmark value. Tier 2 corresponds to unregulated chemicals with toxicity information; slope factors or risk specific doses are used to calculate benchmark values. Tier 3 corresponds to unregulated chemicals without toxicity information. The “Threshold of Toxicological Concern” concept is used to calculate benchmark values. The characterization of chemicals of concern following reverse osmosis in a water reclamation plant and the application of the three-tiered approach for the evaluation of the potential health risks is presented.

The city of Perth in Western Australia is facing a future of compromized water supplies. In recent years, this urban region has been experiencing rapid population growth, coupled with drying climate, which has exacerbated water shortages. As part of the government strategy to secure water sustainability and to address an agenda focused on all elements of the water cycle, a target of 20% reuse of treated wastewater by 2012 was established. This includes a feasibility review of managed aquifer recharge for indirect potable reuse. A characterization of contaminants in wastewater after treatment and an assessment of the health implications are necessary to reassure both regulators and the public. To date, the commonly used approach involves a comparison of measured contaminant concentrations with the established drinking-water standards or other toxicological guidelines for the protection of human health. However, guidelines and standards have not been established for many contaminants in recycled water (unregulated chemicals). This article presents a three-tiered approach for the preliminary health risk assessment of chemicals in order to determine key contaminants that need to be monitored and managed. The proposed benchmark values for the calculation of risk quotients are health based, systematically defined, scientifically defensible, easy to apply, and clear to interpret. The proposed methodology is based on the derivation of health-based levels for unregulated contaminants with toxicity information and a “threshold of toxicological concern” for unregulated contaminants without toxicity data. The application of this approach will help policymakers set guidelines regarding unregulated chemicals in recycled water.