Removal, transport, and transformation of organic micropollutants in managed aquifer recharge: Insights from target and non-target analyses

Managed aquifer recharge (MAR) systems can reduce the stress on groundwater resources by intentionally infiltrating and abstracting (surface) water for drinking water production. Organic micropollutant (OMP) removal and transformation products (TPs) formation in MAR depend on several factors, including their sorption and biodegradation potential. Via target and non-target analyses, we monitored OMPs (parent compounds + TPs) from infiltrated water to abstracted groundwater and drinking water. Our results show that MAR improves water quality, with 61 % of the 31 OMPs in the infiltrated water being removed by >90 %. However, persistent contaminants, including artificial sweeteners and PFAS, were not removed and reached drinking water. The charge state of hydrophilic OMPs determined transport, which was driven by electrostatic interactions with soil: positively charged OMPs were retained near the infiltration point, while negatively charged OMPs travelled to the groundwater abstraction wells. Our results reveal important blind spots in the standard list of priority OMPs measured to assess drinking water quality. Specifically, non-target analysis revealed 50 % more OMPs than those detected using target analysis, and uncovered many overlooked TPs. 46 TPs were detected in groundwater but were absent in infiltrated water, indicating possible OMP biodegradation in MAR. However, 28 possibly persistent TPs were also detected in the MAR system. Therefore, post-treatment technologies targeting persistent and mobile contaminants should be applied to complement MAR at the drinking water treatment plant. Our findings can contribute to optimizing MAR systems for improved OMP removal and highlight the need for a more comprehensive approach to water quality assessment for cleaner drinking water production.