Pilot Trials on Testing and Optimization of Polyethersulfone Membranes for Treatment of Fish Processing Wastewater through Membrane Bioreactor Technology

This study aimed to test and optimize the performance of commercial flat Polyethersulfone (PES) membranes submerged in an aerobic membrane bioreactor (MBR) for treatment of fish process wastewater. Wastewater samples were collected from Makindi fish farm (Nairobi, Kenya) processing unit and transferred to JKUAT-chemistry laboratory for analysis. Tests were conducted for Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), pH, conductivity; Total Dissolved Solids (TDS), phosphate, ammonium and nitrate before treatment to characterize the wastewater. The wastewater treatment process was conducted in a small lab scale MBR unit with a capacity of 97 L. All the operating conditions in the MBR system were optimized. The experiment was carried out in two phases. During the 1st phase, wastewater was directly fed into the MBR aeration tank. During the 2nd phase, a 90 L denitrification tank was introduced to facilitate the reduction of nitrates. The studied commercial submerged flat membrane PES modules showed relatively similar performance for Water Permeability (WP) in the range of 146.6 ± 9(L/m2*h*bar) and 119.8 ± 20(L/ m2*h*bar) for module 1 and 2 respectively, during pilot testing in an aerobic MBR. They were, however, susceptible to fouling that caused a decrease in WP thus affecting the system's efficiency. However, the permeability could be restored by chemical cleaning. COD concentration for permeate was slightly above the maximum allowable concentration of < 100 mg/L as per the WHO guidelines for wastewater reuse for irrigation. However, over 90% COD removal rate was achieved for both modules (line 1 and 2). The level of NO3-N in permeate was within an acceptable range of 5 to 30 mg/L while P-PO43- was lowered to an acceptable range of ≤ 5 mg/L as per the WHO guidelines for wastewater reuse for irrigation. The commercial flat PES membranes were found to be efficient for production of effluent that can be used for irrigation in agricultural fields. The membranes were, however, susceptible to fouling. Therefore in a follow-up study a novel low-fouling membrane will be studied.