Target screening of chemicals of concern in recycled water

Abstract

The results of a characterisation study of water samples collected from an Advanced Water Recycling Plant (AWRP) operating in Perth, Western Australia are presented. The AWRP treats secondary wastewater by ultrafiltration, reverse osmosis (RO) and ultraviolet radiation (UV) to produce recycled water for groundwater replenishment. Water samples collected after RO and UV treatment were characterised by liquid chromatography-high resolution mass spectrometry, using an established protocol for target screening. The target screening of 291 compounds detected a total of 13 chemicals in post-RO and post-UV water, including 2 corrosion inhibitors (4+5-methyl-1H-benzotriazole, benzotriazole), 3 pesticides (metolachlor, propiconazol, prosulfocarb), 3 pharmaceuticals (lamotrigin, metformin, tramadol), 1 personal care product (galaxalidone), 3 artificial sweeteners (saccharin, acesulfame, sucralose) and 1 flame retardant (triethyl phosphate). The corrosion inhibitors benzotriazole and 4+5-methyl-1H-benzotriazole, and the pharmaceutical metformin were detected in hundreds of ng L⁻¹, while the other compounds were present in low ng L⁻¹ concentrations. Analysis of UV treated water samples showed that UV treatment also helped to reduced UV degradable compounds such as the corrosion inhibitors (>50% removal), triethyl phosphate (~50% removal) and the artificial sweetener acesulfame (~95% removal). Overall, the detection of 13 chemicals through target screening analyses did not account for the residual dissolved organic carbon (DOC) in post RO water, the majority of which is still an intriguing unknown. However, the target screening did show that there were no obvious “known” anthropogenic contaminants contributing to the majority of the DOC in post-RO and post-UV treated water. Calculated risk quotients (RQ) for all detected chemicals in UV treated water were 2 to 6 order of magnitude below 1, implying an high degree of safety associated with human consumption of recycled water. Overall the chemicals screening provided further evidence of the overall safety of the use of recycled wastewater treated by RO and UV as a potable water source.