Performance of a Continuous Reactor for Electrochemical Treatment of Pulp Mill Wastewater

The present paper reports the performance characteristics of a continuous electrochemical reactor (ECR) for the treatment of black liquor (BL) discharged from an agri-based pulp and paper mill. The ECR had a working volume of 2 dm³ and used six iron electrode plates with an active electrode area per unit volume of 54 m² m^-3. The ECR operated at an optimal galvanostatic state at a current density of 55.56 Am^-2 with a corresponding cell voltage of ~ 3.1V at near neutral pH without any additives. The residence time (t) in the range of 2-4 h favors the degradation of chemical oxygen demand (COD), color and turbidity. A COD removal of 78.2 and 82.15% was achieved at flow rates of 1 and 0.5 dm³ h^-1, respectively, with a corresponding color removal of ~90 and 79%. The ECR showed good performance at flow rate spikes from 0.5®1®2 dm³h^-1 and 1®2 dm³h^-1 with ~79 and ~73 % COD removal, respectively. The specific energy consumption (SEC) decreased in a narrow range from 16.3 to 14.3 kWh kg^-1 of COD removed for t varying from 4 to1 h. For a charge of 0.625 Ahdm^-3, the current efficiency (CE) values of 310 and 274% were obtained for t = 2 and 1 h, respectively. Batch and continuous study results compared well at t = 2 and 1 h. The ECT showed deterioration in the COD removal efficiency on long time runs with the anode plates swarmed with micro flocs which necessitate their removal.