Sewage sludge as bio fuel

Sewage sludge as bio fuel efficiently uses the amount of energy present inside the sludge itself. The sludge is digested, dewatered and dried to a sludge granulate. The sludge is pre treated by thermal hydrolysis to maximize the sludge degradation, the dewaterability and biogas generation. The strong sludge reduction results in a strong reduction (2 to 4 times) of the amount of water to be evaporated and the energy needed in the drying unit. The amount of electricity and heat needed for all the processes can be generated with the amount of biogas produced during sludge digestion. The wastewater treatment plant is hereby changed from energy consuming to an energy producing plant making use of sludge granulates as bio fuel. The concentrated wastewater (nutrients, micro pollutants) generated during dewatering of the digested sludge is less than 1 % of the total wastewater flow treated in the main process. The concentrated wastewater stream can be efficiently treated in compact reactors, with the possibility to recover and reuse resources as phosphate.The technical and economic feasibility of this concept is proven in a desk study for around 4,300 tons dry matter of sludge.