Performance of biological activated carbon (BAC) filtration for the treatment of secondary effluent: A pilot-scale study

In addition to the adsorption capability for organic compounds, granular activated carbon (GAC) can also serve as a good media for the growth of microbial communities in biofilters. Despite its potential, the application of BAC filtration for municipal wastewater treatment has been little addressed in the literature. In this context, this paper aimed to investigate BAC filtration as a post-treatment of anaerobic effluent in pilot scale and its performance in removing organic matter and turbidity. Removal efficiencies during the biofilters run times and along biofilters depth were also evaluated. Three BAC filters were evaluated under different operating conditions of filtration rates (from 13 to 32 m d(-1)) and empty bed contact time (EBCT) (from 45 to 112 min) during 170 days. The lowest filtration rate (13 m d(-1)) presented the best performance in terms of dissolved organic carbon (DOC) removal (68.2 +/- 4.0%), leading to mean DOC effluent concentration of 6.8 +/- 0,9 mg L-1. The BAC reached the stability of biological activity from the 63rd day of operation, however, the adsorption process was still occurring contributing to DOC removal. These DOC removals were higher than those results reported in the literature for BAC filters treating drinking water and municipal wastewater. The DOC removal efficiencies were maintained during the filter run times, showing the robustness of the system even after the interference caused by the backwashing process. BAC filtration was also capable of removing turbidity, with removal efficiencies between 84.5 +/- 3.6% and 70.63 +/- 6.8% depending on the filtration rate. The results indicated the capability of BAC systems to remove efficiently organic carbon and turbidity from effluents with high organic content, mean of 23.97 (+/- 3.96) mg.L-1, and also valuable support to determine adequate operating parameters for BAC filters application in secondary effluent treatment, such as filtration rate (13 m d(-1)), EBCT (112 min), and detailed backwashing procedures.