Treatment of restaurant wastewater using ultrafiltration and nanofiltration membranes

In this work, two commercial ultrafiltration (UF) membranes, i.e. UF PES-10 kDa and UF PVDF-100 kDa and two nanofiltration (NF) membranes, i.e. NF-90 and NF-270 were used to treat restaurant wastewater discharged from local medium-sized restaurant which served typical Malay halal foods. The wastewater which was subject to membrane treatment process was collected at the point of discharge without undergoing any pre-treatment process. The separation performances of membranes were characterized with respect to BOD5, COD, turbidity and conductivity removal while the membrane sustainability was evaluated based on the water flux recovery. Promising results of COD and turbidity removal (between 97.8 and 99.9%) were able to achieve regardless of membrane type, indicating the size of pollutants contributing to COD and turbidity values are significantly larger than 100 kDa. Removal rates of BOD5 and conductivity were found to be strongly dependent on the membrane pore size. As NF-90 exhibited the smallest pore structure among the membranes studied, it showed the highest BOD5 (86.8%) and conductivity removal (82.3%). In terms of sustainability, it is found that the original water flux of NF-90 was able to be retrieved by >50% compared to between 15 and 38% reported in the UF membranes, after only a simple rinsing process. This indicated that NF-90 is less susceptible to fouling and is more suitable and reliable to be employed for restaurant wastewater treatment.