The objectives of this assignment financed by the World Bank were to: (1) Assess the amount of Carbon Emission Reductions (ERs) that Tunisia's wastewater sector could achieve, focusing on the Greater Tunis, Nabeul-Hamamet, and Sousse areas, and (2) Identify potential and viable Clean Development Mechanism (CDM) wastewater projects. STELLA met with officials from the Ministry of Environment and key stakeholders involved in the wastewater sector (ONAS), and visited selected wastewater treatment plants (Choutrana, Sud-Méliane). STELLA collected relevant data on wastewater treatment plants (WWTP) with a capacity of more than 18,000 people-equivalent, calculated the amount of greenhouse gases (GHG) released due to the current sludge treatment practice, and assessed to what extent these emissions could be reduced. Wastewater CDM projects approved so far by the UNFCCC consist of installing anaerobic sludge digesters and flaring or using the methane produced on site. STELLA also conducted an economic and financial analysis of the potential CDM projects. We compared the economic and financial costs and benefits of anaerobic digestion projects for the six largest WWTP, based on a discounted cash flow analysis over the lifetime of the project. We calculated the Net Present Values (NPV) of each project based on expected revenues (with and without the sale of carbon credits) as well as investment and operation and maintenance (O&M) costs.