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Automatic pH control for anaerobic bacteria of wastewater treatment of paper and pulp industry

Paper and pulp industrial effluents have high lignin content, high concentration of organic halides, low biodegradability and toxicity problems, which can affect the water ecosystem and destroy the species population. Anaerobic treatment for industrial wastewater is widely used in the world. For such a process, pH is a critical factor that affects the activity of these microorganisms. The optimum value of pH for the anaerobic process is (6.8 to 7.2). It is difficult to control the pH, because of non-linearity due to the existence of a logarithmic relationship between pH level and hydrogen ion concentration, and also due to the existence of response lagging and significant overshoot. Focusing on difficulties in pH control, a mathematical model for automatic pH control for anaerobic bacteria of the wastewater treatment plant is established in this paper. Usually, the control strategy depends on the practicality of the process mathematical model. Our approach to solving this problem is to install a cascade control system with a pH control loop and flow rate control loop. The flow control loop controls the flow and ensures the speedy self-stabilization of flow resulting in the elimination of oscillation in neutralizing liquid concentration in a small-time, while the pH control loop that contains a proportional controller adjusts the pH at the value of 7. The pH control loop will be the main loop while the flow controlling loop is the auxiliary loop. Our proposed pH control system has been designed so as to have quick rise time, no overshoot, smooth steady-state performance, small adjusting time, and good precision. It fulfils most of the requirements of automatic pH control systems.