Comprehensive 4E (energy, exergy, exergoeconomic, and exergoenvironmental) analysis and optimization of wastewater sludge gasification: A case study in a resource-constrained area

Global population growth has driven increased energy demand and waste generation, particularly in industrial sectors. This study evaluates the techno-economic feasibility of wastewater sludge gasification (WSG) as a waste-to-energy solution for resource-constrained areas. Comprehensive energy, exergy, exergoeconomic, and exergoenvironmental (4E) analyses were conducted to assess and optimize the WSG process, identifying inefficiencies, costs, and environmental impacts. Sensitivity analyses of key gasification parameters further refined performance, economic viability, and environmental outcomes. In a case study in Kerman, Iranan, the results reveal an overall exergy efficiency of 22.61 %, limited by inefficiencies in the boiler and gasification components, with exergy destruction rates of 47.4 %, 22 %, and 20.9 %, respectively. Optimization of these components is recommended to enhance system efficiency. The study also demonstrates WSG's lower carbon footprint compared to conventional sludge treatment methods (incineration and landfill) and highlights its potential for cost reduction in industrial symbiosis scenarios. Moreover, syngas production was optimized to achieve an ideal hydrogen-to-carbon monoxide ratio for direct reduction iron production, offering a sustainable alternative to traditional steam methane reforming. The findings suggest that integrating WSG with steel production not only addresses local resource constraints but also provides a scalable, cost-effective approach to syngas generation, advancing industrial energy efficiency and waste management in similar regions.