In this paper, a modification is done in Gravitational Search Algorithm (GSA) where an alpha parameter (α) is modified. This modification is done in order to provide different gravitational constant, G(t) and acceleration (a) to each agent as trying to improve its performance. Then this modified GSA algorithm is tested to see the effectiveness of PID controller in finding the value of KP, KI and KD of an activated sludge process (ASP) system in terms of computational time. These results are then compared with the computational time of original GSA approach and Particle Swarm Optimization (PSO) to see the effectiveness of the new approach.