## 3 Results and Discussion  
### Cost-Benefit Analysis of Water Reclamation Projects for Industrial Water Supply  
CBAs of water reclamation projects for industrial water supply were conducted based on wastewater flow rates of 5200, 10,000, 15,000, and 25,000 m\({}^{3}\)/day. The NPVs of water reclamation projects for industrial water supply for cases that included and excluded environmental benefits are shown in Figure 3 (Table S5). The details of the costs and benefits in the NPVs are summarized in Table S6. Considering only the direct costs and benefits resulted in NPVs less than zero in all cases, this indicates that the projects were not economically feasible. The total direct benefits of a project were less than the investment and operation and maintenance costs. However, when the environmental benefits of not discharging WWTP effluents into public waters were considered along with the direct costs and benefits, the NPVs were greater than 0 in all cases except for those with a flow rate of 5200 m\({}^{3}\)/day and discount rates of 5%, 7%, 9% and 11% and those with flow rates of 10,000 and 25,000 m\({}^{3}\)/day and an 11% discount rate. In all cases, the IRRs were smaller than the fixed discount rates when only the direct costs and benefits were considered, as shown in Table 3. Given that the NPVs of the projects were negative in these cases, it was impossible to calculate the IRRs such that the NPVs became zero. By contrast, when the indirect benefits to the environment were considered together with the direct costs and benefits, in most cases, the IRRs were larger than the chosen discount rates, which ranged from 4.6% to 11.5%. Moreover, the selling prices of reclaimed water appeared to have a major impact on project feasibility. If the selling prices of reclaimed water were too low, the projects were not feasible. Therefore, we further determined the minimum selling prices of reclaimed water that would still make the projects feasible. The results are shown in Table 4. In all cases, when only the direct costs and benefits were considered, the minimum selling prices of reclaimed water ranged from 29.73 to 36.24 THB/m\({}^{3}\). By contrast, when environmental benefits were included, the minimum selling prices were 23.23-29.73 THB/m\({}^{3}\), which were lower than the prices without environmental benefits. At these prices, the NPVs became positive, the BCRs were equal to 1, and the IRRs were equal to the selected discount rates. However, these prices were associated with a PP of 20 years. Therefore, selling prices should be set higher to make the investment more profitable and to reduce the PP. These results clearly show that water reclamation projects for industrial water supply within industrial parks are more economically feasible when environmental benefits are included. However, such projects are not economically feasible under all scenarios when only the direct costs and benefits are considered. This consideration aligns with the perspective of industrial parks, where externalities are generally not considered. In other words, water reclamation for industrial water supply is infeasible from the perspective of industrial parks, and thus, it does not provide financial incentives for project implementation. However, from the public's perspective, the benefits outweigh the costs when all aspects, including environmental benefits, are considered. Therefore, the government may