Reclaiming biologically stable water from treated secondary effluent using a dual-membrane system

Abstract

The effectiveness of a lab-scale multibarrier membrane system, comprised of microfiltration (MF) and reverse osmosis (RO) modules, for reclaiming biologically stable water from treated secondary effluent was evaluated under various operating and environmental conditions. The biological stability of reclaimed water was quantified by using assimilable organic carbon (AOC). The results obtained from this study revealed that the RO process was able to reduce AOC more efficiently under either a high operating pressure (>50 psi) or under the condition of a medium recovery ratio (∼20%) with a slightly alkaline (pH ∼ 7.5) operating environment. Generally, the MF could reduce the turbidity of its feed water from 4.1-5.3 NTU to only around 0.3 NTU, which helped to enhance RO operation by slowing down the fouling development rate. The removal efficiencies of the RO, under optimal conditions, was 98.1-98.9% for total organic carbon (TOC) and 96.1-98.7% for AOC, respectively. The observations were compared with the corresponding results obtained from continuous flow experiments, which confirmed that good performance of the membrane system in terms of AOC removal could last for 15-16 days before the fouling phenomenon became severe (i.e., led to a 10-20% decrease in AOC removal). With membrane cleaning, it was able to restore the capability of the RO in terms of TOC and AOC rejections. Under optimal conditions, the AOC level detected in the RO permeate ranged from 10 to 50 μg/L. This observation indicated that a dual-membrane system was able to reclaim biologically stable water from treated secondary effluent. © Mary Ann Liebert, Inc.