Assessing the risk from trace organic contaminants released via greywater irrigation to the aquatic environment

Onsite non-potable reuse of greywater reduces the energy costs associated with the transport of wastewater and the stress on traditional source waters. However, greywater contains trace organic contaminants (TOrCs) that can be harmful to the aquatic environment when released via irrigation. In this work, the risk associated with TOrCs was evaluated for two potential irrigation scenarios, the use of untreated greywater and the use of greywater treated via conventional activated sludge. Risk quotient (RQ) ratios were calculated using the maximum concentration of each compound in the untreated or treated greywater divided by the relevant aquatic predicted no effect concentration. The TOrCs with RQs > 0.1 or 1 were classified as moderate and high priority, respectively. A review of greywater literature showed that a total of 350 compounds have been detected, with 132 classified as moderate or high priority in untreated greywater. Post-treatment 44 TOrCs remained as high priority due to high concentrations in greywater and/or poor removal during treatment, but only 14 of them were detected in multiple geographic locations. The final list of 14 TOrCs includes plasticizers/flame retardants (di-(2-ethylhexyl) phthalate, bisphenol A, and triphenyl phosphate), surfactants/preservatives/fragrances (4-nonylphenol, benzyldimethyl dodecylammonium chloride, tonalide, methylparaben, and 2-6-di-tert-butyl-4-methylphenol), UV-filters (benzophenone-3 and octocrylene), and pharmaceuticals/antibiotics (acetaminophen, trimethoprim, caffeine, and triclosan). This subset of TOrCs would be useful surrogates to monitor during greywater treatment for irrigation as potential hazards for nearby aquatic environments.