Pesticides and other micropollutants are often found in groundwater above the limits set by the EU. To ensure safe drinking water, drinking water production relies on energy-intensive adsorption or advanced oxidation technologies. Biodegradation, the major process for xenobiotics' natural attenuation in the environment, appears as a sustainable and cost-effective solution for this problem. However, anaerobic groundwater environments show low biological activity. Redox condition is of particular interest as redox-dependent biodegradation has been reported for several micropollutants. Nevertheless, most studies on micropollutants biodegradation are performed under aerobic conditions, so little is known about anaerobic micropollutant biodegradation. Therefore, this study investigated the biodegradation of micropollutants by four microbial cultures under five different redox conditions.
A selection of 16 micropollutants frequently found in groundwater was used. The degradation of these micropollutants was investigated under five different redox conditions - aerobic, nitrate, iron and sulfate reducing, and methanogenic, in batches inoculated with microbial cultures from two soils (Ditch and Soil) and two activated sludge (IndustrialAS and MunicipalAS). After about 110 days of experiment, the cultures were re-spiked with micropollutants to study further degradation. The evolution dynamics in the microbial culture was also investigated.
In general, soil cultures performed better than both activated sludge under all redox conditions except aerobic (Figure 1). Aerobic condition resulted in more extensive micropollutant biodegradation and higher number of degraded micropollutants, regardless of the inoculum. Nitrate reducing condition resulted in low removal efficiencies, comparable to the ones observed under sulfate reducing conditions. After re-spiking, an overall slower micropollutant degradation and lower number of micropollutants degraded was observed, indicating that the availability of micropollutants alone did not exert enough selective pressure to cultivate a micropollutant-degrading microbial community. Introduction of oxygen in anaerobic environments or the addition of a co-substrate are approaches worth investigating to increase micropollutant biodegradation.
