Potential power generation from sludge systems for wastewater treatment

Abstract

All waste water treatment systems generate sludge, composed mainly of organic material. The amount of generated sludge per unit mass of organic material depends on the nature of the treatment system (aerobic or anaerobic), on the composition of the organic material in the influent and on the operational conditions. In order to convert the chemical energy of sludge into useful forms of energy there are basically two ways: (1) anaerobic digestion and use of the biogas or (2) thermal processes: direct combustion, pyrolysis or gasification. Na analysis shows that anaerobic digestion is preferable to thermal processes when the objective is generation of electrical power. The energy that can be generated from excess sludge in aerobic processes is clearly insufficient to cover the demand of energy for aeration and heat to evaporate the water of sludge cake before application of thermal processes. In anaerobic systems the potential of energy generation is higher and the demand is lower. Atleast in theory anaerobic system can be self sufficient in trms of energy by using the sludge. The contribution of thermal processes is relatively inexpressive and its application is only justified when it is necessary to reduce the mass of produced sludge to make transport and final destination feasible.