Techno-Economic Feasibility and Greenhouse Gas Emissions Assessment of Composting Versus Biodrying in Mechanical–Biological Treatment: Case Study in Alexandria, Egypt

Egypt’s municipal solid waste (MSW) sector faces persistent challenges due to increasing generation rates, limited recovery, and a high organic fraction, motivating the selection of appropriate biological treatment options within Mechanical–Biological Treatment (MBT) systems. This study compares composting-based MBT and biodrying-based MBT for a case application in Alexandria, Egypt, using an integrated techno-economic and greenhouse gas (GHG) assessment. Discounted cash-flow modelling was applied using defined CAPEX and OPEX, along with revenue from recovered products. GHG accounting used documented emission factors and activity data against an unmanaged landfill baseline representative of current disposal practices. The system boundary covers waste reception and mechanical processing, biological treatment, process energy use, and residual disposal. Results show that composting achieves higher financial performance (NPV USD 2.55 million) than biodrying (NPV USD 0.99 million), while delivering a 48.5% reduction in net system GHG emissions relative to the baseline. Sensitivity analysis indicates that the comparative ranking is primarily driven by electricity prices, revenue assumptions, CAPEX, and baseline-related emissions parameters. Under the defined assumptions, composting is the preferred MBT biological pathway for the analyzed case, and interpretations are limited to the evaluated boundaries.