Influence of intermittent flow on removal of organics in a biological activated carbon filter (BAC) used as post-treatment for greywater

Angelika Hess,Cécile Bettex,Eberhard Morgenroth

doi:10.1016/j.wroa.2020.100078

Angelika Hess, Cécile Bettex + Show 1 more

Open Access

https://doi.org/10.1016/j.wroa.2020.100078

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Abstract

Highly variable flow has to be expected in decentralized greywater treatment and can lead to intermittent operation of the treatment system. However, few studies have addressed the influence of variable flow on the treatment performance of a biological activated carbon filter (BAC). In this study, we investigated the influence of intermittent flow using small-scale BAC columns, which treat greywater as a second treatment step following a membrane bioreactor (MBR). Three operating strategies to respond to variable flow were evaluated. The activated carbon was characterized before and after the experiments in terms of biological activity and sorption capacity. The performance of the BAC filters was assessed based on total organic carbon (TOC) removal, TOC fractions and growth potential. No significant differences were observed between constant flow compared to on-off operation with intermittent flow over the range of tested influent concentrations. Peaks with high TOC during 24 h periods were attenuated by sorption and biological degradation. Adsorbed TOC was released after switching back to normal concentrations for influent concentrations more than 5 times higher than usually observed, the BAC functioned as a temporary sink. In line with these results, the high influent TOC values led to increased biological activity in the filter but did not influence the sorption capacity. The experiments showed that intermittent flow does not negatively impact the performance of a BAC and that there is no need for additional equalization tanks to buffer the variable flow, for example in household-scale greywater treatment.

Highlights

Greywater reuse offers a great water saving potential and in the recent years, interest in greywater treatment and reuse has increased (National Academies of Sciences 2016)
We investigated the influence of intermittent flow using small-scale biological activated carbon filter (BAC) columns, which treat greywater as a second treatment step following a membrane bioreactor (MBR)
The experiments showed that intermittent flow does not negatively impact the performance of a BAC and that there is no need for additional equalization tanks to buffer the variable flow, for example in household-scale greywater treatment

Summary

Introduction

Greywater reuse offers a great water saving potential and in the recent years, interest in greywater treatment and reuse has increased (National Academies of Sciences 2016). We treat the greywater with a conventional membrane bioreactor (MBR) followed by a biological activated carbon filter (BAC). MBRs are often installed as a first treatment step for greywater treatment (Friedler et al, 2006; Jefferson et al, 2004; Wu 2019). A BAC after the membrane reduces the organics and helps to ensure safe water quality (Ziemba et al, 2019). A disinfection step for virus inactivation and removal of pathogens would be necessary to reach water that is hygienically safe. With the chosen treatment configuration we combine physical and biological greywater treatment as suggested in literature (Li et al, 2009)

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