Development of a Spatial Optimization Model for MSW Management by Hydrothermal Carbonization: A Case Study on Dhaka

Hydrothermal carbonization (HTC) is a promising solution to cope with the large amount of municipal solid waste (MSW) produced in densely populated metropolitan areas of developing countries. But technical and logistical limitations typically necessitate optimal plant locations and a strong supply chain for MSW-based HTC plants to be economically attractive. To that end, a novel linear programming (LP)-based spatial optimization model has been developed that takes multiple critical constraints (biomass availability, hydrochar yield, market demand, costs of transporting and handling biomass and hydrochar, and land cost) into account to maximize the net profit of HTC plants. Dhaka, being a mega city, is burdened with the issue regarding disposal of large quantity of MSW. A case study was conducted based on the MSW management system of Dhaka North City Corporation (DNCC) for two schemes, a single (79.26 MWthermal) plant and a double (39.63 MWthermal) plant, in Dhaka city and its surrounding area. The model showed that the single plant scheme generated a higher profit (~18.5 million USD) than the double plant scheme (~17.7 million USD). Locations within Dhaka city near the secondary transfer stations were found to be favorable for plant establishment in both schemes. Further analysis revealed that plants' net profit is highly dependent on their optimal locations, with total transportation cost being the most significant location-sensitive element. Standardized coefficients suggest that for a single plant scheme, total transportation cost will always have a more dominant effect than land cost. This model will be able to guide the policy makers to take necessary steps for proper management of ever-growing city waste by setting up HTC facilities at optimal locations.