Optimized Operational Strategies for Managing Salinity in Reused Drainage Water

Drainage Water Reuse (DWR) is vital for irrigation in arid regions; however, salinity remains a major limit on crop yields and long‑term soil health. This study tests three operating strategies for the Bahr El‑Baqar Wastewater Treatment Plant (WWTP), which mixes differently saline drains and discharges into El‑Salam Canal, itself blending Nile water with agricultural drainage. The strategies seek to improve canal salinity while balancing treatment capacity, operating costs, and agronomic needs. A calibrated hydro‑salinity mixing model simulated three strategies, using seasonal 95th‑percentile flows and TDS to represent conservative winter and summer conditions. In Strategy 1, the WWTP is operated progressively from a single unit (0.8 MCM/d) up to full capacity (5.21 MCM/d) while retaining high‑salinity drains in the influent; despite the 6.5‑fold increase in discharge, canal TDS remains 60–81% above the baseline (875 mg/L), stabilizing at 1431–1585 mg/L and effectively limiting cultivation to salt‑tolerant crops. Strategy 2 replaces these drains with moderate‑salinity sources, enabling operation at the design capacity of 5.6 MCM/d while keeping the Total Dissolved Solids (TDS) within 1039 –1409 mg/L and broadening crop suitability. Strategy 3 operates the WWTP at roughly half capacity (3.0 MCM/d) and supplements canal inflow with additional low‑salinity drainage obtained by expanding the reuse of drains that are currently only partially reused along El‑Salam Canal. This configuration maintains canal TDS at 1165–1205 mg/L (about 33–38% above baseline), a range compatible with many cereals, vegetables, and fruit trees when combined with appropriate leaching, while substantially reducing energy and chemical consumption.