Biological activated carbon filter for greywater post-treatment: Long-term TOC removal with adsorption and biodegradation. (1st December 2021)

• Record Type: Journal Article
• Authors: Hess, Angelika; Morgenroth, Eberhard
• Is Part Of: Water research. Number 13(2021)
• Publication Date: 2021-12-01
• Subjects: Biological activated carbon -- Greywater reuse -- Adsorption -- Biodegradation -- Backwashing; Water supply -- Periodicals; Water-supply engineering -- Periodicals; Water -- Pollution -- Research -- Periodicals; 361.6105
• DOI: 10.1016/j.wroa.2021.100113
• Languages: English
• ISSNs: 2589-9147

Abstract

Highlights: Total organic carbon removal in a biological activated carbon filter for greywater post-treatment monitored over 900 days. Long-term stable total organic carbon removal was demonstrated with around 60% removed. Biodegradation and adsorption overall contributed equally to the total organic carbon removal. Remaining sorption capacity at the bottom of the filter buffered high influent total organic carbon. Little reactor maintenance required: only infrequent backwashing. Abstract: Biological activated carbon (BAC) filters can be used to remove residual total organic carbon (TOC) from greywater after a membrane bioreactor. The two main TOC removal processes are adsorption to the granular activated carbon (GAC) and biological degradation. Biodegradation leads to the growth of microorganisms in the filter bed, which can lead to increased pressure loss over the filter bed. However, the roles of sorption and biodegradation in long-term TOC removal and how they complement each other are unclear. We monitored TOC removal from greywater in a BAC filter installed following a membrane bioreactor over more than 900 days. Removal performance depended on the operational time of the BAC filter, the influent TOC concentration, and in the upper part of the filter on the empty bed contact time (EBCT). Across the overall filter, the EBCT did not significantly influence TOC removal, showing that the filter was sufficiently large for the range of flow rates observed. Analysis of the long-term data revealed the equal importance of sorption and biodegradation over the whole operation period and the whole filter bed. Most of the TOC was removed in the upper part of the filter, where biodegradation was the dominant mechanism. In the lower part of the filter, sorption capacity remained and allowed high influent TOC concentrations to be buffered. The generous filter design with low average filtration rates ensured long-term TOC removal. The only maintenance needed was backwashing, which was required only after more than 800 days of operation. Backwashing effectively reduced the pressure loss but had no significant influence on the effluent water quality. Our study shows that BAC filters are a suitable post-treatment step for the treatment of greywater with highly variable flow and TOC concentrations. Graphical abstract: Image, graphical abstract