## 2 Methods
### Cost-Benefit Analysis of Water Rclamation Projects  
CBA was used to analyze the economic feasibility associated with reclaimed wastewater projects in industrial parks with different flow rate scenarios. The analysis was completed by assessing various indicators: NPVs, IRRs, BCRs, and PPs [15; 40]. The methodology flowchart of the CBA of water reclamation projects in industrial parks, including all of the scenarios conducted in this study, is illustrated in Figure 2. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Direct Costs and Benefits**} & \multicolumn{5}{c}{**Wastewater Flow Rates (m\({}^{3}\)/d)**} \\ \cline{2-6}  & **240** & **480** & **2400** & **3600** & **4800** \\ \hline Volume of reclaimed water produced (m\({}^{3}\)/d) [1] & 240 & 480 & 2400 & 3600 & 4800 \\ \hline
**Direct costs** & & & & & \\ Construction costs (THB million) [2] & 1.4 & 2 & 12 & 16 & 24 \\ Pipeline system costs (THB million) [3] & 0.505 & 0.87 & 2.795 & 2.795 & 5.21 \\ Operating and maintenance costs (million \(\text{THB}/\text{year}\)) [4] & 0.1971 & 0.3942 & 1.971 & 2.9565 & 3.942 \\ \hline
**Direct benefits** & & & & & \\ \hline Reclaimed water prices (THB/m\({}^{3}\)) [5] & 12 & 12 & 12 & 12 & 12 \\ \hline Nitrogen fertilizer price [6] (THB/kg) & 11.5 & 11.5 & 11.5 & 11.5 & 11.5 \\ \hline Phosphorus fertilizer price [6] (THB/kg) & 17.1 & 17.1 & 17.1 & 17.1 & 17.1 \\ \hline \hline \end{tabular} \({}^{(1)}\) We assumed no loss in the water reclamation systems. [2] The construction costs of sand filtration and chlorine contact tank units in water treatment plants are obtained from the Provincial Waterworks Authority of Thailand.  
\({}^{(2)}\) The costs of pipeline installation in Thailand are obtained from contractor companies under the assumption that the water distribution distance was 5 km. [4] [PERSON] et al. (2020) [34]. [5] These are the reclaimed water (second grade water) prices disclosed by an industrial estate. [6] The fertilizer prices are from the Bureau of Agricultural Economic Research, Thailand.  
\end{table} 
Table 2: Information for estimating the direct costs and benefits of water reclamation projects for the irrigation of plants and green areas, consisting of sand filtration and chlorination. NPV is the difference between a project's benefits and its cost over the project's lifetime, as shown in Equation (3). A 20-year lifespan was assumed for all water reclamation plants [13]. Discount rates of 3%, 5%, 7%, 9%, and 11% were used in the analysis, covering the rates commonly used for water projects in Thailand and internationally [13; 41; 42]. In 2020, the Comptroller General's Department, Thailand, recommended the use of a 5% lending interest rate to estimate the reference prices of construction projects. The social discount rate recommended by the Asian Development Bank (ADB) is 9% [43]. For the private sector, discount rates can be considered through weighted average cost of capital analysis to reflect the opportunity cost of private investment, which largely depends on the capital structure of companies and can be as high as 11%. Alternatively, lending interest rates can be adopted as discount rates. In Thailand, for loans from four major commercial banks, the minimum retail rate is 6.75% [44]. However, if projects are eligible to receive loans from the Environment Fund in Thailand, the interest rates are as low as 2-3% [45]. Nevertheless, large private companies can often afford to undertake projects with environmental benefits as their corporate social responsibility projects, regardless of whether they yield no or low profits. Water reclamation projects may fall into this category, where the discount rates used are usually low. Therefore, the discount rates of 3% to 11% were chosen in this study to cover typical ranges of discount rates.