Optimization and PID Control of pH and Temperature in an Electrocoagulation Process

Abstract

In this work, effects of temperature and pH in batch treatment of pulp and paper mill wastewater using electrocoagulation has been investigated. Conductivity, temperature, and pH are selected as controlled variables; supporting electrolyte, cooling water, acid and base flow rates are selected as manipulated variables, respectively. Real time experimental multi input-multi output (MIMO) control of conductivity, temperature, and pH under constant current conditions are achieved using MIMO Proportional Integral Derivative (PID) control algorithms coded in MATLAB™. A central composite design (CCD) has been applied to the system under controlled conditions and optimum pH and temperature values are obtained using response surface methodology (RSM). Both controlled and uncontrolled experiments are performed using optimum values and results are compared in terms of removal efficiencies of pollutants. Results show that 34.47% chemical oxygen demand (COD), 98.06% total suspended solids (TSS), 99.80% turbidity, 99.93% color, and 13.40% SO42- removal is achieved in 45 minutes of process operation under controlled conditions and COD, TSS, turbidity, color and SO42- removal are increased by 10.92, 2.97, 4.06, 2.89, 3.17 respectively in comparison with uncontrolled operation. The highest removal percentages are obtained under controlled operating conditions as 98.5% and 98.3% for turbidity and color, respectively, for 10 minutes operation. It is concluded that optimum process operating conditions for removal of turbidity and color of pulp and paper mill wastewater is obtained under constant 6.45 pH, 23.24 °C temperature, 1.78 mS/cm conductivity, and power consumption is reduced by 25.3% under controlled conditions.