Biodegradation of organic micropollutants in GAC filters – temporal development and spatial variations

The capacity for micropollutant removal in granular activated carbon (GAC) filters for wastewater treatment changes over time, which could be attributed to biodegradation and adsorption. Knowledge on the biological degradation of organic micropollutants, however, is scarce. In this work, the degradation of micropollutants in several full-scale GAC and sand filters was investigated through incubation experiments over a period of three years, using 14C-labeled organic micropollutants with different susceptibilities to biodegradation (ibuprofen, diclofenac, and carbamazepine), with parallel 16S rRNA gene sequencing. The results showed that the degradation of diclofenac and ibuprofen in GAC filters increased with increasing numbers of bed volumes and was highly dependent on the availability of oxygen in the filter. Despite relatively large differences in bacterial composition between filters, the degradation of diclofenac was consistently high in the GAC filters that were operated with high oxygen concentration (> 8 mg/L). A slight increase in the biodegradation of diclofenac was also observed with greater filter depth, as well as for bitumen-based compared to coconut-based GAC. The results of this comprehensive experimental work provide an increased understanding of the interactions between microbial composition, filter material, and oxygen availability in the biodegradation of organic micropollutants in GAC filters.