This study proposes an optimal design method for maximizing the sustainability of an integrated wastewater treatment plant with a combined heat and power generation system. The proposed system is analyzed based on thermo-environ-economic analysis to investigate the effects of the components' efficiencies, temperature differences in the heat exchangers, and pressure ratio of the compressor and gas turbine. The multi-objective genetic algorithm is used to minimize the thermoeconomic and environmental objective functions, which are assumed as the total cost rate and total environmental impact obtained from exergy, annual cost rate, and life-cycle assessment analyses. The optimization results showed that the total cost rate and environmental impacts are decreased by 16.9% and 5.3%, respectively. The power generated by the optimized system can cover 47% of the power demand of wastewater treatment plant as well as the total heat requirement of the system. (C) 2017 Elsevier Ltd. All rights reserved.