NON-TARGETTED SCREENING OF WASTEWATER DISINFECTION BY PRODUCTS USING SILICONE PASSIVE SAMPLERS

Abstract

To reuse or not to reuse treated municipal wastewater effluent is still an open question. Answer of this question lies in detailed health and environmental risk-benefit analysis. Circularity of water is an emerging idea that is at the very heart of water conservation. Wastewater treatment offers treated wastewater with a quality that should be beneficial for reuse. Typically, wastewater treatment involves several steps such as biodegradation of organic matter, precipitation of suspended solids, nutrients removal, and disinfection to inactivate or kill pathogenic microorganisms. However, disinfection process produces a wide-range of chemicals referred to as disinfection by-products (DBPs), which are of health and environmental concern. Only a dozen of DBPs are regulated for monitoring in the developed world. Whereas the number of DBPs produced during disinfection may be in thousands. This makes complete health and environmental risk-benefit analysis of disinfected effluent a daunting challenge for monitoring agencies. In this study, I illuminated a pathway which helps scientist overcome the challenge of resolving the complexity around the question of safe reuse of wastewater. I integrated innovative passive sampling, chromatographic, mass spectrometric and computational approaches for monitoring the complete spectrum of DBPs. I started with the developing an estimation model to predict polydimethylsiloxane (PDMS)-water partition coefficient: a property needed to calculate the concentration in water phase by measuring concentration on passive sampling phase (PDMS). The model, which was based on 2-parameters linear free energy relationship (2p-LFER) between partition coefficients of PDMS-water, and octanol-water and air-water systems, exhibited 𝑅2=0.96 and 𝑅𝑀𝑆𝐸=0.38 log unit. Next, PDMS passive samplers deployed at Al-Wathba 2 Wastewater Treatment Plant, Abu Dhabi, United Arab Emirates for 30 days at the disinfection (chlorination) tank. Passive samplers were analyzed using comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-ToF-MS) technique at National Institute for Environmental Studies, Tsukuba, Japan. The raw chromatograms were deconvolved into five layers using Non-Negative Matrix Factorization (NMF)-based algorithm. Filters such as occurrence in replicates, absence in field blank, match score with the reference library were used to increase in the confidence of detection of DBPs. As a result, I screened 32 DBPs which might be present in the wastewater effluent with high probability. Lastly, I carried out the risk assessment of detected DBPs for the attributes of persistence, bioaccumulation and toxicity (PBT) using U.S. Environmental Protection Agency’s Estimation Program Interface (EPI Suite™) version 4.11. Several DBPs detected in the wastewater were flagged for the PBT concern, indicating the wastewater reuse for agriculture and landscaping might not be a safe practice. This indeed calls for further studies for targeted quantification and in-depth health and environmental risk assessment.