Abstract
In traditional waste load allocation (WLA) decision making, water quality-related constraints must be satisfied. Fuzzy models, however, can be useful for policy makers to make the most reasonable decisions in an ambiguous environment, considering various surrounding environments. We developed a fuzzy WLA model that optimizes the satisfaction level by using fuzzy membership functions and minimizes the water quality management cost for policy decision makers considering given environmental and socioeconomic conditions. The fuzzy optimization problem was formulated using a max–min operator. The fuzzy WLA model was applied to the Yeongsan River basin, which is located in the southwestern part of the Korean Peninsula and Korean TMDLs were applied. The results of the fuzzy model show that the pollutant load reduction should be increased in the Gwangju 1 and Gwangju 2 wastewater treatment plants (WWTPs) and in subcatchments with high pollutant load. In particular, it is necessary to perform advanced wastewater treatment to decrease the load of 932 kg ultimate biochemical oxygen demand (BODu)/day in the large-capacity Gwangju 1 WWTP and reduce the BODu emission concentration from 4.3 to 2.7 mg/L during the low-flow season. The satisfaction level of the fuzzy model is a relatively high at 0.81.
Highlights
The general waste load allocation (WLA) model allocates the pollution load for each sewage treatment plant or each subcatchment by obtaining a solution to the optimization problem consisting of the constraints on river water quality and the objective function for the watershed water quality management cost
The pollution load reduction across the entire basin was relatively small based on WLA results, which suggests that the river water quality is close to the target water quality; the satisfaction value was large
WLA model developed considering theThe pollutant loadquality reduction pollution load reduction cost were expressed as membership functions, and a fuzzy WLA problem and satisfaction level associated with river water quality in a basin
Summary
The general waste load allocation (WLA) model allocates the pollution load for each sewage treatment plant or each subcatchment by obtaining a solution to the optimization problem consisting of the constraints on river water quality and the objective function for the watershed water quality management cost. The existing WLA decision-making problem optimizes the objective function while necessarily satisfying the constraints on water quality and the wastewater treatment efficiency. Various types of traditional WLA models have been developed using optimization techniques such as linear programming, nonlinear programming, and genetic algorithm, and these models mainly focus on economic factors such as water quality management costs [1,2,3]. In addition to the economic goal of cost minimization, two types of inequalities among waste dischargers in the basin were considered for WLA. The second type of inequality involved the fairness in the distribution of treatment efforts among waste dischargers [4]
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