Treatment of micropollutants in municipal wastewater using white-rot fungi
Treatment of micropollutants such as pharmaceuticals and pesticides in municipal wastewater is challenging due to their very low concentrations (ng/l to µg/l), their relatively low biodegradability, and their different physico-chemical characteristics. One potential way to improve micropollutant biodegradation in wastewater treatment plant (WWTP) effluent is by using microorganisms such as white-rot fungi that produce powerful unspecific oxidative exo-enzymes (laccase, peroxidase) that are able to oxidize several micropollutants recalcitrant to bacterial degradation. The goals of this study were (i) to evaluate the ability of white-rot fungi to degrade pharmaceuticals and pesticides and (ii) to develop a fungal treatment which allows removal of a broad range of pollutants but also long-term survival of the fungus in the system. For the first objective, batch experiments with the white-rot fungus Trametes versicolor were conducted first in defined medium containing glucose and spiked with 10 mg/l of pollutant (naproxen, sulfamethoxazole or isoproturon), and then in real unsterile WWTP effluents (not spiked) with wheat straw as sole carbon and energy source. T. versicolor was able to remove over 90% of naproxen in less than 24 h, and sulfamethoxazole and isoproturon in less than 4 d in defined media spiked with these pollutants. In real unsterile biologically treated wastewater, T. versicolor could remove over 90% of the anti-inflammatory drugs diclofenac and mefenamic acid in less than 24 h, and naproxen in less than 48 h, despite their low concentrations (400-800 ng/l). These good removal rates were however not observed for other compounds that needed longer reaction times, due to the short survival (one week) of the fungus in unsterile wastewater. To increase the chance to maintain this organism in the treatment, we designed a fungal unsaturated biotrickling filter composed of wood chips colonized by the mycelium of the white-rot fungi T. versicolor or Pleurotus ostreatus. Unsterile tap water or treated wastewater spiked with pollutants (10 mg/l) were then trickled with recirculation through the wood-mycelium support. This system allowed a much better survival of the two fungi and was able to remove almost completely naproxen, diclofenac, mefenamic acid, paracetamol, bisphenol A, and triclosan in less than 8 h. Future experiments will show whether the oxidation potential of these fungal filters is applicable to a wider range of pollutants.