STUDIES ON FOULING OF CROSSFLOW MEMBRANES

Abstract

Water, as we all know, is the basic need of life and it covers around 71% of the earth’s surface. But availability of fresh water, which is required by humans, is very less (<1%) and increasing population makes the problem even worse. Also the used water or wastewater contains many constituents which are detrimental to environment and hygiene, hence its safe disposal is also required. So in order to survive in this scenario, we have to recycle and reuse the used water again and again and hence the requirement of treatment of wastewater begins. Initially, the wastewater treatment plant (WWTP) were used to be of large size but with increasing population the cost of area become more and more. Hence we have to reduce the area required by WWTP. In this context, membrane bioreactors (MBRs) are only few decade old advancements. They are much compact than their predecessors as they eliminates many units which are there in conventional WWTP. The quality of their effluents is also higher. In spite of having many advantages, the cost of membranes and fouling in membrane become a constraint in the development of MBRs. However, in recent years, the mass scale production of production of membranes has decreased their cost significantly. Hence, the fouling in membrane remains the most important obstacle in the development of MBRs. The main focus of present study is to present the details of fouling in MBR and analyse the suitability of MBR for medium strength synthetic wastewater treatment. At MLSS around 4000 mg/L, flow rate was decreased from around 42 mL/min to around 10 mL/min in 420 minutes while at MLSS around 7200 mg/L the same decrement occurred in 300 minutes for submerged MBR. At MLSS around 4000 mg/L, flow rate was decreased from around 5 mL/min to around 1 mL/min in 255 minutes while at MLSS around 7700 mg/L the same decrement occurred in 105 minutes for side-stream MBR. Hence, the fouling rate of the membrane increases with increase in the MLSS concentration. The COD removal efficiency for submerged and side – stream MBRs at steady state were around 97% and 98% respectively. The BOD removal efficiency for submerged and side – stream MBRs at steady state were around 91% and 96% respectively. The nutrient removal efficiencies at steady state were more than 90% in both the submerged and side - stream MBRs. So based on these results we can say that the side – stream MBRs are better than submerged MBRs as far as permeate quality is concerned