Electrochemical degradation of pulp and paper industry waste-water

BACKGROUND: Conventional biological waste-water treatment techniques are insufficient to degrade large quantities of dissolved lignin discharged by small-scale paper mills. The current investigation is aimed at comparing the overall performance of basic electrochemical reactor configurations such as batch, batch recirculation, recycle and single pass systems, in removing the organic part of waste-water from a small-scale, agro-based paper industry. The effect of current density, supporting electrolyte concentration, duration of electrolysis, specific electrode surface and fluid flow rate on the removal of pollutants and energy consumption are critically evaluated. The improvement in biodegradability of the effluent during treatment is also noticed. RESULTS: The batch recirculation mode of operation was found to be superior in comparison with a batch system using the same specific electrode surface for both COD removal (73.3 vs. 64%) and capacity utilization (rate constant 1.112 x 10(-3) vs. 1.049 x 10(-3) cm s(-1)). The pollutant removal performance of the batch recirculation system improved considerably with increase in the circulation flow rate. At the best operating point in the recycle system, 59% of COD was removed, corresponding to a current efficiency of 68.9% and specific energy consumption of 18.46 kWh kg(-1). The biodegradability index of the waste-water was improved from 0.18 +/- 0.01 to 0.36 +/- 0.01. CONCLUSION: A recycle reactor was the best configuration, because of its flexibility of operation. Circulation flow rate and withdrawal flow rate enable the control of transfer coefficients and treatment duration respectively. Electrochemical treatment not only removes the bulk of the organic matter, but also makes the remaining pollutants more easily biodegradable. (c) 2009 Society of Chemical Industry