An exergoeconomic analysis of a wastewater treatment plant: investigation and optimization of sludge drying—a case study

The primary parameters in wastewater treatment plant applications are pollutant removal in compliance with standards and energy costs. This study conducts exergy, exergoeconomic, and optimization analyses on the Konya Wastewater Treatment Plant to enhance its energy efficiency. All assessments of the plant were based on actual operational data. Numerical calculations were executed using Engineering Equation Solver software. Exergoeconomic analyses were performed using the Specific Cost Method, while optimization calculations employed the Net Present Value approach. Thermodynamic calculations revealed that the exergy efficiency of the biogas engine was 30.8%, which increased to 39.8% when integrated into a cogeneration system. The overall exergy efficiency of the plant was calculated to be 35.3%, which rose to 58.6% when stabilized sludge was utilized as fuel. During the optimization phase, various drying systems were evaluated, and a hybrid greenhouse-solar-panel drying system was identified as the optimal model. The analyses indicated that the total cost was minimized at the maximum dryness value (70%), suggesting that the greenhouse-type drying system could achieve regional conditions. Compared to thermal and solar energy systems, hybrid systems have been observed to offer significant advantages in first-year costs. Optimization studies reveal that hybrid systems provide 41% greater cost savings in initial investment and operational expenses compared to thermal systems, and 29% greater savings compared to solar energy systems. Meeting the system's energy demand with fossil fuels results in annual emissions of 76,850 tons of CO₂ and 1500 tons of harmful pollutants, equivalent to removing 19,000 cars from traffic or preserving 7300 hectares of forest. Significant soil and ecosystem degradation also occurs. The use of solar energy substantially reduces these environmental impacts, improving air quality and conserving natural resources.