In this work, a new model was developed to quantitatively evaluate and compare anaerobic/anoxic/aerobic (A(2)O) and reversed A(2)O processes for municipal wastewater treatment using projection pursuit method based on particle swarm optimization (PSO). The optimal projection direction was obtained by optimizing the projection index function using the PSO algorithm. By fitting the logistic equation, the evaluation model was established. Then, the calculated ranks of the evaluation samples were computed. The overall performance of both A(2)O and reversed A(2)O processes were evaluated using the established model as a case study. The results show that the mean rank of the A(2)O process (1.79 +/- 0.39) was lower than that of the reversed A(2)O process (1.97 +/- 0.41), indicating that the former was better than the later under the same operating conditions. Through resolving multi-factor evaluation problems, such a PSO-based model is demonstrated to be effective to quantitatively assess wastewater treatment processes. (C) 2016 Elsevier B.V. All rights reserved.