Physical and economical evaluation of laboratory-scale membrane bioreactor by long-term relative cost–benefit analysis

Abstract

Two laboratory-scale single-stage submerged membrane bioreactors (MBRs) were operated in parallel to examine the effect of different flux conditions and several fouling mitigation methods. After control operation (filtration only), three fouling control methods (relaxation, standard backwash and chemical backwash) at 27 litres per m2 per hour (LMH) flux and four different flux conditions (54, 36, 27 and 18 LMH) with standard backwash were applied. Physical performance of MBRs was evaluated based on the operational duration to reach maximum transmembrane pressure and the volume of permeate produced during the operational duration. Then relative cost–benefit analysis was carried out. Results showed that the combination of chemical backwash and standard backwash was the most effective for fouling mitigation in terms of physical improvement of MBR performance. However, the combination proved less economical (400% + α relative cost) than standard backwash alone (343% relative cost), because of the additional cost for pumps and chemicals. It also showed that lower flux (18 LMH) is desirable as it showed better physical performance (1,770% improvement as compared to the highest flux, 54 LMH) and proved more economical than higher flux configuration. Therefore, it is concluded that the operation with standard backwash at the lowest possible flux is the best combination to improve MBR performance as well as long-term cost–benefit. HIGHLIGHTS Many studies focus mainly on high-cost, high-performance techniques without economic justification. But this research focused on the interpretation of performance improvement made by several fouling control methods in terms of relative cost as well as physical performance.; Chemical backwash supported by standard backwash showed the best physical performance among the other operations with different fouling control methods. However, the best operation in physical performance was proven to be less economical than standard backwash operation, because it showed higher long-term cost than that of standard backwash operation.; Therefore this study suggested one of useful tools to justify any fouling control methods in MBR research field not only by physical performance but also by cost-benefit.;

Keywords

• cost–benefit analysis
• economical evaluation
• fouling control
• membrane bioreactor
• performance evaluation