Abstract: This research aims to determine the appropriate effluent tax scheme and construct an optimized mathematical decision making model in order to maximize profits while bearing economic and environmental constraints in the Thachin River basin. The Thachin River is ranked as the most polluted river in Thailand where pig farms, urban communities, aquaculture and industries significantly contribute to deteriorating water quality in the basin. Therefore, the comparison of applied mathematical models for uniform and non-uniform taxation were developed, This approach can prohibit the amount of pollution discharges from exceeding the total maximum daily loading of the river. As the results, the mathematical models indicated that applying the uniform tax policy is effectively more saving of 45.25% than the non-uniform tax policy in total expenses. By modifying the uniform taxation model to consider the amount of end-of-pipe pollution emissions, the aggregate amount of wastewater contaminant in the surface water and constraints of waste loading can be prohibited from exceeding the carrying capacity of the river ecosystem.