Quantitative Relative Chemical Assessment to Support Risk Frameworks for Water Recycling

Water resources around the world are increasingly affected by the pressures of population growth and climate change, with substantial risks of water shortages for public supply, agriculture, energy generation, and industry, with impacts on freshwater ecology. Thus, many water utilities are turning to or considering water recycling to augment existing supplies. It is incumbent on a utility to demonstrate that augmenting its water supply with recycled water does not create undue excess risk compared to existing sources that are considered protective of public health. This research quantified the chemical risks associated with using recycled water as a source of water supply. Linear cancer slope factors and threshold dose values were used with chemical concentrations measured at an advanced water recycling pilot in the southern UK to quantify chemical risk profiles of six waters: two existing drinking water source waters, a secondary treated wastewater effluent serving as the influent to the advanced water treatment pilot, and after each treatment step in the pilot (ultrafiltration, reverse osmosis, and ultraviolet advanced oxidation). This study builds on previous work by considering risks throughout the advanced water recycling treatment train via Monte Carlo simulation and evaluating several approaches to handling censored data sets; the analysis leveraged data from an extensive sampling campaign including 37 cancer risk chemicals and 289 threshold-based risk chemicals. Overall, conclusions around relative risk were relatively insensitive to the approach used for handling censored data, while using a stochastic method provided improved insights into the variability of risk. Cancer and noncancer risk profiles of water treated through the advanced treatment train were comparable or better than existing water supply works source waters. This finding provides strong evidence that use of highly treated recycled water as a source of supply is protective of public health from chemical risks when compared to existing source water supplies.