Evaluation of Contaminant Removal of Reverse Osmosis and Advanced Oxidation in Full-Scale Operation by Combining Passive Sampling with Chemical Analysis and Bioanalytical Tools

Abstract

Advanced water treatment of secondary treated effluent requires stringent quality control to achieve a water quality suitable for augmenting drinking water supplies. The removal of micropollutants such as pesticides, industrial chemicals, endocrine disrupting chemicals (EDC), pharmaceuticals, and personal care products (PPCP) is paramount. As the concentrations of individual contaminants are typically low, frequent analytical screening is both laborious and costly. We propose and validate an approach for continuous monitoring by applying passive sampling with Empore disks in vessels that were designed to slow down the water flow, and thus uptake kinetics, and ensure that the uptake is only marginally dependent on the chemicals' physicochemical properties over a relatively narrow molecular size range. This design not only assured integrative sampling over 27 days for a broad range of chemicals but also permitted the use of a suite of bioanalytical tools as sum parameters, representative of mixtures of chemicals with a common mode of toxic action. Bioassays proved to be more sensitive than chemical analysis to assess the removal of organic micropollutants by reverse osmosis, followed by UV/H₂O₂ treatment, as many individual compounds fell below the quantification limit of chemical analysis, yet still contributed to the observed mixture toxicity. Nonetheless in several cases, the responses in the bioassays were also below their quantification limits and therefore only three bioassays were evaluated here, representing nonspecific toxicity and two specific end points for estrogenicity and photosynthesis inhibition. Chemical analytical techniques were able to quantify 32 pesticides, 62 PCPPs, and 12 EDCs in reverse osmosis concentrate. However, these chemicals could explain only 1% of the nonspecific toxicity in the Microtox assay in the reverse osmosis concentrate and 0.0025% in the treated water. Likewise only 1% of the estrogenic effect in the E-SCREEN could be explained by the quantified EDCs after reverse osmosis. In comparison, >50% of the estrogenic effect can typically be explained in sewage. Herbicidal activity could be fully explained by chemical analysis as the sampling period coincided with an illegal discharge and two herbicides dominated the mixture effect. The mass balance of the reverse osmosis process matched theoretical expectations for both chemical analysis and bioanalytical tools. Overall the investigated treatment train removed >97% estrogenicity, >99% herbicidal activity, and >96% baseline toxicity, confirming the suitability of the treatment train for polishing water for indirect potable reuse. The product water was indistinguishable from local tap water in all three bioassays. This study demonstrates the suitability and robustness of passive sampling linked with bioanalytical tools for semicontinuous monitoring of advanced water treatment with respect to micropollutant removal.

Chemicals in reverse osmosis-treated wastewater: occurrence, health risk, and contribution to residual dissolved organic carbon

“…Thus the majority of NDMA exposure for humans is not from drinking water consumption and the increased risk to human health from NDMA provided by drinking water consumption is still relatively minor. Our assessment of a low health risk from ROtreated WW agrees with other assessments undertaken using multiple bioassays (Van Buynder et al 2009;Escher et al 2011;Macova et al 2011). In particular, screening undertaken during the project using a cytokinesis-block micronucleus assay with a human lymphoblastoid cell-line indicated that there was no significant cytotoxicity or genotoxicity for either secondary wastewater or RO-treated wastewater (Van Buynder et al 2009), and the toxicity of RO-treated WW has been shown to be indistinguishable from that of drinking water .…”

Effect-based trigger values for in vitro bioassays: Reading across from existing water quality guideline values

“…A similar approach for the oxidative stress response quantified with the AREc32 bioassay resulted in a provisional EBT-EC IR1.5 of 3 REF . Both provisional EBT-EC were able to suitably differentiate between water quality before and after advanced water treatment in recycling In contrast to integrative assays, the majority of receptormediated effects (e.g., inhibition of enzymes or activation of hormone receptors) can typically be explained by known chemicals (Escher et al, 2011;Leusch et al, 2005Leusch et al, , 2014bRutishauser et al, 2004;Tang and Escher, 2014). Effects can be expressed as socalled bioanalytical equivalent concentrations (BEQ), which represent the concentrations of a reference chemical that would elicit the same effect as the water sample of unknown composition.…”

Pesticide impact on aquatic invertebrates identified with Chemcatcher® passive samplers and the SPEARpesticides index

“…Time-weighted average concentrations (c TWA ) of pesticides in the water phase were calculated from a generic sampling rate for all target compounds (Escher et al, 2011) Chemcatchers were the sampling devices of choice for this study because they reliably detect polar and semi-polar pesticides in surface waters (Schäfer et al, 2008a(Schäfer et al, , 2008bShaw et al, 2010;Stephens et al, 2005). An SDB-RPS Empore disk modified with sulfonic acid groups was applied as receiving phase to detect hydrophilic and semi-hydrophilic chemicals with log K OW b 4 (Gunold et al, 2008;Moschet et al, 2015;Sanchez-Bayo and Hyne, 2014;Stephens et al, 2005;Vermeirssen et al, 2008).…”

“…For the calculation of c TWA , we propose the use of a generic sampling rate (as suggested by Escher et al (2011) in another context), additionally corrected for specific hydrodynamic conditions at each sampling site, which would make the use of Chemcatchers even easier.…”