Wastewater reclamation charges and expenses on treatment processes contribute largely to total site operating and capital costs. Hence, the problem of optimizing wastewater treatment plant is vital for economy and environment. The paper addresses single-stage optimization based approach for designing optimal wastewater treatment network (WWTN). The proposed method consists in solving optimization model of WWTN superstructure. To cope with complex nonlinear problem a direct stochastic random search technique has been employed. The contribution addresses designing method and example of application.