## 3 Results and Discussion
### Cost-Benefit Analysis of Water Reclamation Projects for the Irrigation of Plants and Green Areas  
Water reclamation for the irrigation of plants and green areas provides several direct and indirect benefits, including revenues from the sale of reclaimed water, savings on fertilizer costs due to the nitrogen and phosphorus contents in reclaimed water, and environmental benefits from not discharging WWTP effluent into public waters. Feasibility studies of water reclamation projects for the irrigation of plants and green areas in industrial parks with post-treatment processes consisting of sand filtration and chlorine disinfection were conducted under wastewater flow rates of 240, 480, 2400, 3600, and 4800 m\({}^{3}\)/day. The NPVs were greater than 0 in all cases, regardless of whether the indirect benefits to the environment were included or not (Figure 6, Table S7). The details of the costs and benefits in the NPVs are summarized in Table S8. Notably, the investment and operation and maintenance costs were much lower than those for water reclamation projects for industrial water supply, as membrane units were not included in the treatment system. The selling prices of reclaimed water (12 THB/m\({}^{3}\)) appeared to be high. As a result, the benefits exceed the investment and operation and maintenance costs. Nevertheless, when the indirect benefits to the environment were included, the NPVs were greater than the analyses that considered only the direct costs and benefits. In all cases, the IRRs were higher than the fixed discount rates (Table 5). When only the direct costs and benefits were considered, the IRRs ranged from 45.5% to 69.2%. When indirect environmental benefits were included, the IRRs ranged from 68.0% to 103.3%. Further, the BCRs were greater than 1 in all cases, as shown in Figure 7 (Table S7), ranging from 2.44 to 3.78 when only the direct costs and benefits were considered, and from 3.42 to 5.30 when environmental benefits were included. Figure 6: NPVVs for water reclamation projects for the irrigation of plants and green areas when including and excluding environmental benefits (EB). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Flow Rate (m3/d)** & **Exclude EB** & **Include EB** \\ \hline
240 & 45.5\% & 68.0\% \\ \hline
480 & 60.5\% & 90.2\% \\ \hline
2400 & 58.6\% & 87.5\% \\ \hline
3600 & 69.2\% & 103.3\% \\ \hline
4800 & 59.4\% & 88.6\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Internal rates of return for water reclamation projects for the irrigation of plants and green areas when including and excluding environmental benefits (EB). Figure 7: Benefit–cost ratios (BCRs) for water reclamation projects for the irrigation of plants and green areas when including and excluding environmental benefits (EB). As shown in Figure 8 (Table S7), the PPs ranged from 1.5 to 2.7 years when only the direct costs and benefits were considered, and they were between 1.0 and 1.7 years when the indirect environmental benefits were considered together with the direct benefits. In summary, the PP was always less than 3 years, indicating a good investment. According to the feasibility analyses, all cases were highly cost-effective. Table 6 shows that the minimum selling prices were well below 12 THB/m\({}^{3}\) in all cases. For cases where only the direct costs and benefits were evaluated, the minimum selling price of reclaimed water ranged from 3.06 to 4.83 THB/m\({}^{3}\). At these prices, the NPVs became positive, the BCRs were equal to 1, and the IRRs were equal to the selected discount rates. Moreover, the minimum selling price decreased to zero when environmental benefits were included. In other words, reclaimed water used for the irrigation of plants and green areas can be offered free of charge. The NPVs were positive at these prices, and the BCRs were 1.01-1.57. The IRRs were 11.3-18.8%, well above the discount rates used, while the PPs were 5.7-18.9 years.