Optimizing Dissolved Oxygen and Sludge Retention Time via ASM1 Simulation for Energy and Emission Reduction in Tropical Multi-Industrial WWTPs Toward Net Zero.

Energy optimization in multi-industrial wastewater treatment plants (WWTPs) located in tropica regions remains challenging due to highly fluctuating loading conditions and the lack of long-term operational datasets. This study employed a 365-day dataset (156 samples) to calibrate (270 days, 116 samples) and validate (95 days, 40 samples) Activated Sludge Model No. 1 (ASM1) using SUMO 24 software for energy optimization at an industrial park WWTP in northern Ho Chi Minh City, Vietnam. The study aimed to support energy optimization and emission reduction strategies toward the Net Zero 2050 target. The calibrated model demonstrated good predictive performance for TCOD, TSS, TN, and NH4 +-N (R2 = 0.75-0.92; NSE = 0.50-0.88; MAPE = 15.2%-25.1%). Energy auditing revealed that the biological treatment system accounted for 50.6% of total electricity consumption, with aeration alone contributing 37.2%. A total of 35 simulation scenarios based on the DO × SRT matrix (DO: 1.5-4.5 mg/L; SRT: 3-7 days) identified the optimal operating region at DO = 1.5-2.5 mg/L combined with SRT = 5-7 days. A three-phase pilot study was subsequently implemented: Phase 1 (P1) increased SRT (5 → 7 days), which stabilized nitrification and expanded the TN safety margin from 3.9% to 7.5%; Phase 2 (P2) reduced DO (3.0 → 2.0 mg/L), resulting in a 17.66% reduction in energy consumption (34,831 kWh/year; 76.63 million VND/year) and a decrease of 21.72 tCO2e/year in emissions while maintaining a TN safety margin of +14.8%; and Phase 3 (P3) (DO 2.0 → 1.5 mg/L) was rejected because it caused nitrification instability, reduced the TN safety margin to 6.7%, and increased the sludge volume index (SVI) beyond 120 mL/g. Therefore, P2 (DO = 2.0 mg/L; SRT = 7 days) is recommended for full-scale implementation at the plant. The proposed framework integrating ASM1 simulation, energy auditing, emission assessment, pilot validation, and a Net Zero roadmap demonstrates strong scalability for similar industrial WWTPs across Southeast Asia.