Process control is an important part of wastewater treatment plants which is important for a plant to work at optimum conditions because it enhances lifetime of a plant and also reduce unit product cost. Process control may be as simple as on/off valve that is triggered upon offset of the system measured parameters from the desired set point. Different controllers are used in wastewater treatment plants such as combination of proportional, integral and derivative systems and also proportional/integral controls. Selection of controller is on the basis of high stability, fast response and also minimum disturbance to the system. This review is presented for commonly used and newly developed control and instrumentation in reverse osmosis and multistage flash distillation. This review paper introduces the control systems and integrated process simulation environment software used for optimization of wastewater plants.