Submerged nanofiltration of biologically treated molasses fermentation wastewater for the removal of melanoidins

The possibility and efficiency of submerged nanofiltration (SNF) in the removal of melanoidins from the biologically treated molasses fermentation wastewater were evaluated in this study. Submerged filtration tests were conducted with biologically treated molasses fermentation effluent employing lab-made membrane modules manufactured from lab-fabricated flat-sheet thin-film composite polyamide nanofiltration membranes with a molecular weight cut-off (MWCO) of about 580 Da. Treatment efficiency in terms of color removal, permeate flux as well as COD reduction was investigated under different trans-membrane pressures (TMPs) and various volume concentrating factors (VCFs). The results showed that melanoidins could be effectively removed from the biologically treated molasses fermentation wastewater by submerged nanofiltration and the electrolytes presented in the effluent were nearly not retained by the membrane, so that the nanofiltration membrane module could be operated under a low suction pressure. Both the removal efficiency of melanoidins and the reduction ratio of COD increased with the increase of TMP and/or VCF at the expense of water permeability. Steady flux of 3.90 L/m2 h, color removal ratio of 99.5% and COD reduction ratio of 93.8% could be achieved by the submerged nanofiltration system operated under the TMP of 0.8 bar and VCF of 4.0. Furthermore, under the same VCF, compared with the pressurized nanofiltration system (PNF), the SNF system is more anti-fouling and easily to be physically cleaned.