Technical and Economical Evaluation of a Thermal, and Two Oxidative Techniques for the Reduction of Excess Sludge Production

Abstract

Municipal wastewater treatment is closely linked with the production of sludge. This production may be reduced by combining a sludge disintegration technique with a conventional biological reactor, such as an activated sludge. The disintegration techniques are based on mechanical, electrical, thermal, thermo-chemical, biological and oxidative treatments. This work tries to give an evaluation of the efficiency and the economics of disintegration techniques that have demonstrated their potential to reduce the excess sludge production when combined to an activated sludge plant fed with a real urban wastewater. A high ESP reduction rate is achievable (more than 40%) by using disintegration technique such as a thermal (95°C), an ozonation or a hydrogen peroxide treatment. These three disintegration techniques were studied in details in our laboratories. The experiments carried out provided the technical data in order to make an assessment of the economics of the three selected combined processes. The ozone appeared to be the most interesting route for sludge reduction but the heating route is also economically competitive with conventional sludge treatment and disposal especially if stringent constraints on the sanitary quality of the sludge are imposed.