Hydrogen supplementation enhances microbial removal of selected organic micropollutants, reduces associated ecotoxicity, and improves nutrient removal in domestic wastewater effluent.

Organic micropollutants (OMPs) compose a group of emerging contaminants that occur in environmental waters at trace concentrations (μg/L to ng/L) with suspected adverse effects on ecosystems and human health. Conventional wastewater treatment plants (WWTPs) are not designed to eliminate the more recalcitrant OMPs. As such, WWTP-effluents are a major source of OMPs in the aquatic environment, and sustainable advanced treatment options are required. One option concerns the biodegradation of OMPs, but several studies show that it might be constrained by the residual low energy content in effluent waters. Since molecular hydrogen (H2) has been identified as a universally available energy source utilised by various bacteria in oligotrophic environments, supporting mixotrophic growth, we examined the hypothesis that H2 can enhance OMP-removal and concomitant ecotoxicity from domestic wastewater effluent. To this end, a lab-scale biological trickling filter supplemented with H2 (1.5% in the aeration with ambient air) was operated in continuous mode for treating a field-collected domestic WWTP-effluent. In total, 51 OMPs were detected in the WWTP-effluent, of which azithromycin and clarithromycin contributed to 76.5% of the total ecotoxic effects, as demonstrated in a cyanobacterial growth inhibition assay. The H2-supplemented trickling filter enhanced the removal of azithromycin and clarithromycin by (69.5 ± 1.5)% and (46.0% ±2.9)%, respectively, and increased the reduction of total OMP-associated ecotoxic effects by 56.5%, compared to the non-H2-supplemented control. Moreover, H2 supplementation improved PO43- and NO3- removal by a factor of 2.3 and 1.5, respectively. These findings demonstrate that H2 supplementation may support microbial processes involved in OMP-removal from domestic wastewater in a microbial treatment system, thereby reducing concomitant ecotoxicity.