Predicted feasibility and economic return of drainage water recycling in an arid region

Significance of using drainage water (DW) is rising as freshwater resources are under growing pressure around the world, particularly in arid regions like Khuzestan province in Iran, which faces both water scarcity and excessive agricultural DW disposal predicaments. Drainage water recycling (DWR), capturing and storing DW for reuse as supplemental irrigation, is becoming increasingly popular due to its ability to fulfill both production and environmental objectives. In this context, a theoretical study was conducted to predict the impact of DWR on sugarcane yield within Amirkabir Agro-industry. The study also aimed to suggest an optimal proportion of reusable DW, taking into account the highest overall economic and environmental benefits. For this purpose, an all-inclusive index named the comprehensive profitability of consumed water (CPCW) was introduced and employed to incorporate various critical attributes of DWR system, in terms of crop yield, cost opportunity, disposal cost, and environmental impacts. Demonstrating an optimal ratio of 23 % for recycled DW, the study showed a 19% reduction in sugarcane yield resulting from a 45% increase in irrigation water salinity, leading to the highest CPCW index. The calculated water savings can increase alternate opportunity costs to supplement irrigation for downstream date orchards (28780 ha) or wheat fields (86400 ha). The reduction in drainage disposal costs had a significant impact on improving the CPCW index. To comply more with the priorities of the farmers, a more reasonable reduction of 15% in the crop yield was considered, which led to 20 % proportional recycled DW. This practice reused 323 Mm3 of drainage water. A sum of 666 Mm3 of water from Karun River was conserved through this practice. Overall, the proposed DWR practice has proven highly effective in substantially reducing the adverse environmental consequences of DW disposal to downstream natural water bodies.