Biological activated carbon (BAC) filters can be used as post-treatment for greywater to remove residual total organic carbon (TOC). The two main TOC removal processes are adsorption to the GAC and biological degradation. Biodegradation leads to the growth of microorganisms in the filter bed that can lead to increased pressure loss over the filter bed. However, the importance of sorption and biodegradation and how they complement each other is unclear for long-term TOC removal. In this study, we monitored TOC removal in a BAC filter that followed a membrane bioreactor for greywater treatment over more than 900 days. The removal performance depended on the operational time of the BAC filter, the influent TOC concentration, and for the upper part of the filter on the empty bed contact time (EBCT). For the overall filter, the EBCT did not significantly influence the TOC removal, showing that it was designed sufficiently large for the different flow rates observed. The analysis of the long-term data revealed equal importance of sorption and biodegradation if considered over the whole operation period and the whole filter bed. In the upper part of the filter, where most of the TOC was removed, TOC was mainly removed by biodegradation. In the lower part of the filter, sorption capacity remained and allowed to buffer high influent TOC concentrations. The generous filter design with low average filtration rate ensured long-term TOC removal. Backwashing, as the only maintenance needed, was required only after more than 800 days of operation. Backwashing the BAC filter effectively reduced the pressure loss but had no significant influence on the effluent water quality. With this study, we could show that BAC filters are a suitable post-treatment step for greywater treatment with its highly variable flow and TOC concentrations.
