Evaluation of the hybrid system combining electrocoagulation, nanofiltration and reverse osmosis for biologically treated textile effluent: Treatment efficiency and membrane fouling

Abstract

The efficiency of the hybrid electrocoagulation-nanofiltration-reverse osmosis (EC-NF-RO) system for the treatment of biologically treated textile effluent was investigated. The treatment performances and membrane fouling behaviours of nanofiltration (NF) and hybrid EC-NF systems were compared. EC process was evaluated concerning mitigate the membrane fouling and increasing the removal efficiencies. Besides, the treated wastewater with the hybrid EC-NF process was finally processed using RO process for reuse purpose in the textile industry. The EC treatment was applied using Fe and Al electrodes at various conditions; pH:4-10, current density:0.5-17 mA/cm2 and operating time:30-180 min. Fe electrode showed better performance in terms of higher removal efficiencies (76% COD, 96% DFZ436), lower energy (21.1 kWh/m3) and electrode consumptions (3.7 kg/m3) for the optimum conditions. Scanning Electron Microscopy-Energy Dispersive Index (ESEM-EDX) and Fourier-Transform Infrared Spectroscopy (FTIR) analyses were carried out for EC sludge samples obtained with Fe and Al electrodes. Desal 5 DL and NF 270 membranes were tested in terms of removal efficiency and membrane fouling for NF and hybrid EC-NF process of textile wastewater. Membrane fouling was evaluated with flux values, resistance-in-series model results as well as Atomic Force Microscopy (AFM), FTIR and contact angle measurements. NF 270 membrane achieved better chloride (28%) and conductivity (41%) removal efficiencies for NF treatment. EC pretreatment did not result in any noticeable improvement in rejections except for chloride (48%) and conductivity (59%) for the hybrid EC-NF process with NF 270. The ratios of Rc decreased to 40% for NF 270 and 42% for Desal 5DL after EC pretreatment. NF270 membrane indicated high permeate flux and low membrane fouling considering cake resistance distribution, surface roughness, hydrophilicity and chemical structure variation. >93% COD, 99% conductivity, 97% chloride, and 91% TDS removal efficiencies were obtained with the hybrid EC-NF-RO process. Finally, the obtained high quality water by RO after the EC + NF 270 hybrid process could be used for all textile finishing process.