The possibility of reusing excess sludge treated by hydrothermal reaction for the purpose of improving the efficiency of the enhanced biological phosphate removal (EBPR) process was investigated. Excess sludge from a fish-processing industry located in Japan was treated in high-temperature and high-pressure water, at a reaction temperature ranging from 200 to 400 degrees C, a pressure of 1.8 to 30MPa and a constant reaction time of 7 min. For the conditions tested, the results showed that when the reaction temperature was increased the content of readily biodegradable substrate in the total CODCr increased. In addition, the amount of some volatile fatty acids (VFAs) produced by the hydrothermal reaction increased as reaction temperature increased. From the phosphate release tests under anaerobic conditions, it was possible to demonstrate that not only the VFAs, but also the readily and slowly biodegradable substrates are used as potential carbon source by the phosphate-accumulating organisms (PAOs).2312935