The optimum operational condition of membrane bioreactor (MBR): cost estimation of aeration and sludge treatment

A methodology to obtain the most economical operational condition of membrane bioreactor (MBR) is developed. In order to achieve the optimum design parameters of MBR with which operational costs are minimized, aeration and sludge treatment costs were estimated for various operational conditions. Generally sludge treatment cost and aeration cost were inversely proportional to each other, which means sludge treatment cost is minimized when aeration cost is maximized and vice versa. Therefore, there might exist an optimum point between the two extreme cases. However, sludge treatment cost turned out to overwhelm the aeration cost over the reasonable operational conditions. Therefore, sludge minimization was considered to be a key for the economical operation of MBR. In the case of typical municipal wastewater of which COD was 400 mg L−1, steady-state MLSS was expected to increase from 11,000 to 15,000 mg/L without sludge removal when HRT was decreasing from 16 to 12 h. For the range of operational conditions considered in this study, economically optimum HRT and target MLSS were turned out to be 16 h and 11,000 mg/L, respectively. Under this condition, aeration for the biodegradation of organic matters would be 13.3 m3 air/min when influent was 1000 m3/day.