Sewage sludge production in Egypt is continuously increasing. Therefore, the pressing needs are to find/develop more efficient, economic and sustainable technologies for sludge treatment. For many years, the main attention was devoted only to sludge drying processes, mainly through natural drying beds, without any interest to sludge quality. Recently, there is an increasing interest in the application of anaerobic sludge stabilization and power generation. The main objectives of this paper are to evaluate and compare the application of aerobic and anaerobic digestion processes for sewage sludge stabilization with respect to various parameters including energy balance, environmental impacts, sludge capacities and economic aspects. Moreover, the area of application for aerobic/anaerobic digestion processes according to the Egyptian conditions is evaluated. The study showed that, while continuous operation of the aerobic digestion process requires approximately 1176 kWh/ton of dry digested solids, the energy recovery from the anaerobic digestion process is estimated to be 667 kWh/ton electrical energy and 678 kWh/ton thermal heat. The economic analysis showed that, the anaerobic digestion process becomes more cost effective for wastewater treatment plant of capacity greater than 40,000 inhabitants (8000 m3/day) under Egyptian conditions. Furthermore, the life cycle assessment analysis demonstrates that the anaerobic digestion process is the most environmentally friendly for all tested environmental impact categories. |
