Investigating the formation and fate of micropollutant transformation products in subsurface water systems

Because of climate change, the Netherlands is currently facing seasonal problems with freshwater provision. Alternative water sources, such as surface water and wastewater treatment plant effluents, are being infiltrated to replenish aquifers and store water. However, micropollutants are widespread in the environment, including groundwater and surface water. The infiltration of alternative water sources may introduce more micropollutants into aquifer systems, threatening the quality of the drinking water produced. Furthermore, there is increasing concern on the underground formation, through microbial processes, of micropollutant transformation products (TPs), which can be more harmful than the parent compounds.

Technological challenge

During the travel time in the subsurface and once in groundwater systems, the fate of micropollutants is affected by biotic and abiotic processes. Microorganisms can biodegrade the contaminants changing their structure and forming TPs or mineralizing them into CO2 and water. TPs can be more recalcitrant and mobile than the parent compounds, but are more difficult to identify, and are thus considered an important blind pot. Under the most favorable conditions, indigenous microbial population may be able to complete the mineralization of contaminants and their TPs. Biodegradation of micropollutants and TP formation is indeed affected by a wide range of parameters, including redox conditions, dissolved organic carbon (DOC) availability and contaminant concentration (Figure 1). In groundwater systems, the conditions (i.e. anaerobic and oligotrophic) are
such that do not support biodegradation. However, the presence of micropollutants and TPs in drinking water sources is most unwanted. By providing DOC or more energetically favorable electron acceptors, biodegradation in subsurface water systems may be stimulated. Moreover, by testing different contaminant concentrations, it may be possible to understand if the microbial transformation of contaminants into TPs is due to metabolic or cometabolic processes. This understanding will be useful to find possible solutions to steer
biodegradation towards mineralization.

In the present research, laboratory experiments and field investigation will be closely interconnected and used to assess TPs fate and formation in subsurface
water systems. The analysis of data and samples from case studies in the Netherlands will be critical to reach this aim and provide useful insights for a
safer production, storage and reuse of water in the future.