Hydrothermal and Pyrolysis Treatment for Sewage Sludge: Choice from Product and from Energy Benefit1

AbstractBiowastes such as sewage sludge usually have high moisture contents and thermal technologies such as pyrolysis and incineration will meet the trouble of heavy evaporation load. Hydrothermal treatment has been adopted as an energy-effective method for dewatering and avoiding water evaporation. In addition, hydrothermal treatment can involve the carbonization of sewage sludge, leaving the stabilized solid product, therefore acting as a final treatment step for sewage sludge disposal. As an energy convertor, pyrolysis is a competitive technology to incineration. In this research products and energy balance for operating the hydrothermal process within temperature range of 220-270 oC were compared with those of pyrolysis process operating within 250-700 oC for sewage sludge disposal. It has been found that the hydrothermal treatment produces less solid product (char) & gas than pyrolysis process and is more energy efficient. However, it requires a rigid high pressure reactor