In wastewater treatment processes, the emphasis has recently shifted to include reduction of energy costs and sludge production in the efficient removal of micro-organisms and viruses. Anaerobic processes consume less energy than aerobic processes, since no aeration is required. In addition, bacteria have slower growth rates under anaerobic conditions, hence producing less sludge.
To meet discharge standards, anaerobic effluent is also subject to downstream post-treatment. Membrane filtering is an ideal process for this treatment since it can achieve a high-quality effluent. The article considers membrane modules submerged in the upper part of the upflow anaerobic sludge blanket (UASB) reactor.
Whether the treatment process is aerobic or anaerobic, membrane fouling is always a major limitation in the membrane separation process. This limitation leads to a decrease in permeate flux or an increase in transmembrane pressure (TMP). Air sparging and intermittent permeation have been widely used as membrane-cleaning methods in aerobic processes. In UASB reactors, however, the effluent contains less suspended solids and more dissolved solids (of a wide range of sizes). The authors therefore aim to determine the effects of air sparging and intermittent permeation on the reduction of membrane fouling in a submerged anaerobic membrane reactor. The anaerobic effluent characteristics, such as mean particle size, surface charge and soluble extracellular polymeric substances (EPS), were evaluated in order to explain the membrane fouling mechanisms. The optimal fouling reducing method was determined according to membrane fouling tendency and energy consumed.
The authors examine the effects of air sparging and intermittent permeation on membrane foulding tendency individually. A comparison between the two methods is made utilising the rate of increase of TMP.
Experiments indicated that intermittent permeation is more effective than air sparging in the reduction of membrane fouling. In addition, the intermittent permeation process was shown to consume less energy. The authors propose optimal operating conditions of a 25 L/m2 h flux and an idle time of 4 minutes with every 10-minute filtration, in order to alleviate membrane fouling and achieve low energy consumption.