Biological degradation of organic micropollutants in GAC filters–temporal development and spatial variations
Maria Takman, Alexander Betsholtz, Åsa Davidsson, Michael Cimbritz, Ola Svahn, Stina Karlsson, Stine Karstenskov Østergaard, Jeppe Lund Nielsen, Per Falås
Abstract
The capacity for organic micropollutant removal in granular activated carbon (GAC) filters for wastewater treatment changes over time. These changes are in general attributed to changes in adsorption, but may in some cases also be affected by biological degradation. Knowledge on the 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 biological degradation (ibuprofen, diclofenac, and carbamazepine), with parallel 16 S rRNA gene sequencing. The results showed that the degradation of diclofenac and ibuprofen in GAC filters increased with increasing numbers of bed volumes when free oxygen was available in the filter, while variations over filter depth were limited. Despite relatively large differences in bacterial composition between filters, a degradation of diclofenac was consistently observed for the GAC filters that had been operated with high influent oxygen concentration (DO >8 mg/L). The results of this comprehensive experimental work provide an increased understanding of the interactions between microbial composition, filter material, and oxygen availability in the biological degradation of organic micropollutants in GAC filters. Organic micropollutants are emitted to aquatic environments via for example municipal wastewater, with potential unwanted environmental effects. These compounds can be removed through filtration with granular activated carbon (GAC). The removal takes place primarily through adsorption, but also through biological degradation. Biological degradation is challenging to confirm, due to difficulties to differentiate between degradation and adsorption in GAC filters. In this study, degradation of organic micropollutants was confirmed in several GAC filters and the microbial community was analyzed. Factors that substantially improved the degradation were identified, and the study can thus improve the removal of hazardous compounds in GAC filters.