Addition of organic waste plant material to digestors in municipal wastewater treatment plants

The combined anaerobic digestion of waste plant-material and sewage sludge at waste water treatment facilities seems to be an interesting idea for the reduction of disposal problems and at the same time to advantageously make use of the waste plant-material's energy potential. Bench and pilot scale experiments showed that sufficient grinding and a high moisture content are important in order to avoid operational problems in the combined digestion process. Waste plant volatile solids up to 70% of the raw sewage sludge volatile solids may be added. Results obtained at waste water treatment plant 'Selb', Federal Republic of Germany are presented.