Thermodynamic and thermoeconomic analysis and optimization of sludge digestion and dewatering systems in wastewater treatment plants

This thesis study investigates the thermodynamic and exergoeconomic analysis and optimization of sludge digestion and dewatering systems using operational data from the Konya Wastewater Treatment Plant. All analyses, from the inlet of wastewater to the sludge drying process, were performed using the Engineering Equation Solver (EES) program, and efficiency losses as well as potential improvement areas were identified. Based on the identified losses, improvement strategies were proposed with the aim of optimizing the exergy efficiency of the system. The results of the exergy analysis indicate that the exergy efficiency of the biogas engine is 30.8%, and that the total efficiency increases to 39.8% when a cogeneration system is employed. The overall exergy efficiency of the plant was calculated as 34.3%, and it was observed that this value increases to 56.9% when stabilized sludge is used as fuel. Exergoeconomic analyses were conducted based on the Specific Exergy Costing (SPECO) method, and the results show that the desulfurization unit has the highest exergoeconomic factor. This indicates that a significant portion of the component cost arises from capital investment and operating expenses. The results of the exergoeconomic analysis were evaluated in terms of cost and efficiency to improve the overall system performance. Within the scope of the optimization study, sludge drying systems were examined, with a particular focus on hybrid drying systems. To determine the optimum costs, analyses considering performance and area constraints were carried out, and the most cost-effective drying model was identified as a greenhouse-type hybrid drying system supported by solar panels. The analyses demonstrate that, under regional conditions, the hybrid drying cost reaches its minimum at the maximum achievable dryness level of 70% for greenhouse-type drying. Keywords: Exergoeconomic analysis, Exergy, Sludge drying, Thermodynamics, Wastewater treatment