Development of intergrated electrocoagulation and membrane process for water reclamation from biotreated palm oil mill effluent

Abstract

Electrocoagulation (EC) is a simple, environmentally friendly and cost effective process, when integrated with membrane filtration, becomes very attractive for developing a sustainable water reclamation system. The critical parameters namely initial pH, time and current density largely impact the EC process efficiency. Few works have been done on observing the interaction of these critical parameters and the possible combined effect on the overall pollutant removal efficiency. Also, with membrane pore blocking study, the efficiency of the overall integrated process can be enhanced by determining the dominant fouling mechanism. Therefore, the knowledge of the combined effect of critical parameter interaction followed by membrane fouling study would enhance the overall efficiency of the integrated process to sustainably reclaim water. Using aluminum electrodes with interelectrode distance of 10 mm, with a set range of initial pH, current density, and time of 3-8, 40-160 mA/cm2 and 15-60 minutes, respectively, the effect of the three critical variables were investigated on synthetic wastewater, representing biotreated palm oil mill effluent (BPOME). Next, a pore blocking study was undertaken with the EC treated BPOME after crossflow membrane filtration process with transmembrane pressure of 0.5 bar and pore size of 1 kDa. The optimum Chemical Oxygen Demand (COD) removal of 71.5% was determined at pH 6, current density of 160 mA/cm2 (with current 1.75 A) at EC time of 15 minutes. The experiment was validated with real BPOME, resulting in the removal efficiency of 60.7% COD, 99.91% turbidity, 100% total suspended solids (TSS) and 95.7% color. The interaction of parameters observed in this study indicated a synergistic contribution of initial pH and current density in removing maximum wastewater COD in 15 minutes of EC. After following with membrane ultrafiltration process, the COD removal increased to 71.7%, and the dominant fouling mechanism prevailing was cake formation as determined by fitting with Hermia’s pore blocking models. EC with activated carbon (AC) addition, run with the optimized parameters, significantly improved the final treated quality with a 100% TSS, 99% of both color and turbidity and 84.6% COD removal. The best permeate quality was achieved with 1 wt. % addition of AC in EC reactor, and the removal of TSS, turbidity and color was nearly 100% and COD was removed 99.7% with final value of 5±1 mg/L, which are within the range of reusable process water standard. Also, addition of AC in EC, sustainably enhanced the final treated effluent quality with fouling mitigation in the subsequent membrane ultrafiltration.