Economic and Environmental Assessment of Sewage Sludge Treatment Processes Application in Egypt

The sewage sludge production in Egypt is rapidly increasing resulting from the continuous increase of population, urban planning and industrial developments. This sludge needs to be adequately treated and environmentally managed to reduce the negative impacts of its application or disposal. Therefore, the main currently pressing needs are to find/develop more efficient, economical and sustainable technologies for sludge treatment. The main objectives of this study are to evaluate and compare the application of aerobic/anaerobic digestion, natural/mechanical dewatering and composting processes in sewage sludge treatment options in Egypt with respect to various parameters including energy balance, environmental impacts, sludge capacities and economic aspects. Moreover, the area of application of each treatment process, according to the Egyptian conditions, is evaluated. The Life cycle assessment methodology was applied to assess and compare the environmental impacts of the treatment processes to find out the environmental critical points and to provide a technical and scientific support to the municipal authorities for the environmental optimization of sludge management. The study shows that the application of anaerobic digestion process with energy recovery is proven to be a promising option for sewage sludge stabilization in Egypt. It has the lowest costs and environmental impacts due to the energy recovery. The using of rice straw as a bulking agent in the windrow composting of sewage sludge could help to some extent in reducing the environmental problems arising from the disposal of this agricultural residue. The application of anaerobic digestion process becomes more cost effective for wastewater treatment plants (WWTPs) capacities greater than 40,000 inhabitants (8000 m/day). Whereas, the drying beds process was more cost effective with WWTPs capacities less than 90,000 inhabitants under Egyptian conditions. Keyword: Anaerobic digestion, aerobic digestion, windrow composting, environmental impacts, economic aspects, area of application, life cycle assessment.