Clemencia Rodriguez

Indirect Potable Reuse: A Sustainable Water Supply Alternative

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.

Recycled water: potential health risks from volatile organic compounds and use of 1,4-dichlorobenzene as treatment performance indicator.

Characterisation of the concentrations and potential health risks of chemicals in recycled water is important if this source of water is to be safely used to supplement drinking water sources. This research was conducted to: (i) determine the concentration of volatile organic compounds (VOCs) in secondary treated effluent (STE) and, post-reverse osmosis (RO) treatment and to; (ii) assess the health risk associated with VOCs for indirect potable reuse (IPR). Samples were examined pre and post-RO in one full-scale and one pilot plant in Perth, Western Australia. Risk quotients (RQ) were estimated by expressing the maximum and median concentration as a function of the health value. Of 61 VOCs analysed over a period of three years, twenty one (21) were detected in STE, with 1,4-dichlorobenzene (94%); tetrachloroethene (88%); carbon disulfide (81%) and; chloromethane (58%) most commonly detected. Median concentrations for these compounds in STE ranged from 0.81 μg/L for 1,4-dichlorobenzene to 0.02 μg/L for carbon disulphide. After RO, twenty six (26) VOCs were detected, of which 1,4-dichlorobenzene (89%); acrylonitrile (83%) chloromethane (63%) and carbon disulfide (40%) were the more frequently detected. RQ(max) were all below health values in the STE and after RO. Median removal efficiency for RO was variable, ranging from -77% (dichlorodifluoromethane) to 91.2% (tetrachloroethene). The results indicate that despite the detection of VOCs in STE and after RO, their human health impact in IPR is negligible due to the low concentrations detected. The results indicate that 1,4-dichlorobenzene is a potential treatment chemical indicator for assessment of VOCs in IPR using RO treatment.

Occurrence of iodinated X-ray contrast media in indirect potable reuse systems

A lack of knowledge of the health and environmental risks associated with chemicals of concern (COCs) and also of their removal by advanced treatment processes, such as micro-filtration (MF) and reverse osmosis (RO), have been major barriers preventing establishment of large water recycling schemes. As part of a larger project monitoring over 300 COCs, iodinated X-ray contrast media compounds (ICM) were analysed in treated secondary wastewater intended for drinking purposes. ICM are the most widely administered intravascular pharmaceuticals and are known to persist in the aquatic environment. A direct injection liquid chromatography tandem mass spectrometry (DI–LC–MS/MS) method was used to monitor secondary treated wastewater from three major wastewater treatment plants in Perth, Western Australia. In addition, tertiary water treated with MF and RO was analysed from a pilot plant that has been built as a first step in trialling the aquifer recharge. Results collected during 2007 demonstrate that MF/RO treatment is capable of removing ICM to below the analytical limits of detection, with average RO rejection calculated to be greater than 92%. A screening health risk assessment indicated negligible human risk at the concentrations observed in wastewater.

A Proposed Approach for the Assessment of Chemicals in Indirect Potable Reuse Schemes

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.

A Review of On-Site Wastewater Treatment Systems in Western Australia from 1997 to 2011

On-site wastewater treatment systems (OWTS) are widely used in Western Australia (WA) to treat and dispose of household wastewater in areas where centralized sewerage systems are unavailable. Septic tanks, aerobic treatment units (ATUs), and composting toilets with greywater systems are among the most well established and commonly used OWTS. However, there are concerns that some OWTS installed in WA are either performing below expected standards or failing. Poorly performing OWTS are often attributed to inadequate installation, inadequate maintenance, poor public awareness, insufficient local authority resources, ongoing wastewater management issues, or inadequate adoption of standards, procedures, and guidelines. This paper is to review the installations and failures of OWTS in WA. Recommendations to the Department of Health Western Australia (DOHWA) and Local Government (LG) in regard to management strategies and institutional arrangements of OWTS are also highlighted.

Assessing Health Risks from Pesticides in Recycled Water: A Case Study of Augmentation of Drinking Water Supplies in Perth, Western Australia

ABSTRACT A characterization of pesticides in secondary treated effluent (STE) and a screening health risk assessment were conducted to evaluate potential health impacts of recycled water for potable reuse. Samples of STE were examined pre- and post-reverse osmosis (RO) treatment in two plants. Risk quotients (RQ) were estimated by expressing the maximum and median concentration as a function of the health value. Of 128 pesticides analyzed, 11 were detected in STE. Trifluralin was detected in 86.5% of the STE samples followed by metolachlor (67.6%), 2,4-D (50%), and propiconazole (42.5%). Metolachlor was the only pesticide detected post-RO in one sample (0.08 μg/L, limit of reporting = 0.05 μg/L). RQ(max) were all below health values in the STE with the exception of thiophanate methyl (RQ max = 2.4). RO was able to reduce the concentration of all pesticides below LOR. Median removal efficiency for RO ranged from 67.1% (atrazine) to 98.8% (2,4-D). The results indicate that, despite the detection of pesticides in STE, the impact on indirect potable reuse is negligible due to the low concentrations in STE and their subsequent removal during RO treatment. Implementation of risk management strategies to optimize safety and recommendations for a monitoring program are also discussed.