TREATMENT OF PULP AND PAPER INDUSTRY WASTEWATER BY ELECTRO-COAGULATION

Abstract

Pulp and paper industry is a water intensive chemical process industry and generates significant quantities of wastewater (20 to 250 m3 per ton of paper) containing high concentration of lignin and its derivatives, fatty acid, tannins, resin acid, sulphur compounds, phenol and its derivatives etc. Remediation of these pollutants is of special concern due to their highly toxic and persistent nature. Due to the low biodegradability index (less than 0.4) of pulp and paper industry wastewater, biochemical methods are not so efficient for the treatment of this effluent. Further, other conventional techniques such as adsorption, chemical oxidation, etc. require chemicals and produce secondary pollutants, thus, efforts are on for the development of effective treatment technique for the treatment of pulp and paper industry wastewater around the world. In recent years, electro coagulation (EC) technique has got strong research interest because it produces coagulants in situ by dissolving electrodes in the cell, which helps the removal of the pollutants producing negligible secondary pollutants. Under the above discussion, the present study has been undertaken for the effective treatment of pulp and paper industry wastewater by electro-coagulation. In the continuing search to achieve the desired objective, synthetic and industrial wastewater was treated by electro-coagulation using aluminum as a sacrificial electrode. A central composite design (CCD) was used to design the experiment sequences for both synthetic and industrial wastewater to study the interactive influences of parameters on the removal efficiency of pollutants as mention below. Batch experiments were performed to study the removal of lignin from synthetic wastewater and removal of TOC, COD and colour from industrial wastewater. Characterization of aluminium electrodes were carried out using various techniques such as FE-SEM and EDAX. Effect of various parameters such as current density, pH, NaCI concentration and time on the removal of lignin from synthetic wastewater has been investigated to determine the optimum process condition for maximum removal of lignin. The optimum condition for lignin removal was found to be current density 100 A/m2, pH 7.6, NaCl conc. 0.75 mg/l and time 75 min. Effect of various parameters such as current density, pH, inter-electrode distance and time on the removal of TOC, COD and colour from industrial wastewater has been investigated to determine the optimum process condition for maximum removal of pollutant mention above. The optimum condition for TOC, COD and colour removal from industrial effluent was current density 115 A/m2, pH 7, inter-electrode distance 1.5 cm and time 75 min. The analyses of result were carried out by ANOVA for both synthetic and industrial wastewater. The regression models were developed for lignin removal from synthetic wastewater and TOC, COD and colour removal from industrial wastewater. These analysis suggest the quadratic models for lignin removal from synthetic wastewater and TOC, COD and colour removal from industrial wastewater. The confirmation experiments were also conducted to compare the result of analytical findings and experimental investigations. A complete characterization of sludge which produce during electro-coagulation also have been carried out. The FTIR, TGA, DTA ,SEM and EDAX analysis were carried out which show that these may be use for combustion purpose.