Application of Novel Low-Fouling Membranes for Fish Processing Wastewater Treatment and Comparison to PES Commercial Membranes in a Lab Scale Membrane Bioreactor

Abstract

This study aimed to apply a novel low-fouling membrane that was tested for the first time for treatment of fish processing wastewater in a Membrane Bioreactor (MBR) system. The aim was to demonstrate its improved performance and ability to resist fouling as part of a follow-up work where two studied commercial PES membrane modules showed significant fouling problems. A novel low fouling membrane was prepared by coating the surface of a PolyEtherSulphone (PES) membrane with a Polymerisable Bicontinuous Microemulsion (PBM). Performance test for PES membranes and PBM-coated membranes were conducted in an automated Ultrafiltration (UF) cross-flow testing cell using humic acid as model foulant. Further tests were conducted in a lab scale MBR unit. Characterization of chemical and surface properties of the two tested membranes was carried out using Attenuated Total Reflectance Infrared (ATR-FTIR) spectrophotometer and Contact Angle Measurements (CAM). The IR spectra confirmed the presence of PBM coating on the coated membranes while contact angle measurements demonstrated low contact angles indicating that hydrophilic property was achieved for the modified PBM membrane. The cross-flow fouling test showed low color intensity deposited on PBM coated membrane thus better resistance to fouling as was further confirmed with MBR experimental results which also showed the higher average COD removal efficiency of 96 ± 1.1% for PBM module in comparison to 92 ± 4.9% observed with the PES membrane module. The two tested PES and PBM membrane modules had COD in permeate mainly within the maximum allowable concentration of < 100 mg/L as per the WHO guidelines for wastewater reuse for irrigation. Percentage removal rate for nitrogenous compounds and P-PO4 3- in permeate was 88.1 ± 1% and 83.6 ± 1% for PBM membrane module and 84.5 ± 2% and 69.3 ± 3% for PES module respectively. PES membrane module showed significant fouling at critical flux of 7.3L/m² at TMP of 230 mbar in comparison to PBM module whose flux remained constant at higher flux above 350 mbar. This was an indication that PBM module had improved ability to resist fouling for a longer time and might be more economical in the long run for use in iMBR for the production of effluent to be used for irrigation agricultural fields.