The effect of hydrothermal reaction temperature, time and solid-liquid ratio on the physicochemical properties of excessive sludge was investigated during the hydrothermal pretreatment of excessive sludge. The results showed that the dissolution rate of CODCr
and the reduction of sludge increased with the increasing of hydrothermal reaction temperature. At 200 ℃, the dissolution rate of CODCr
was the highest, 96.5% higher than that of the raw sludge. The maximum reduction of sludge was 80.1% and the ammonia nitrogen changed irregularly. The hydrothermal time had little effect on the reduction of sludge and the dissolution of ammonia nitrogen. When the hydrothermal time was 1 hour, the dissolution rate of CODCr
reached the highest, 96.5% higher than that of the raw sludge. When the solid-liquid ratio was 10%, the dissolution of ammonia nitrogen reached the least of 1.093mg/g after hydrothermal pretreatment. By comprehensively investigating the effect of the three factors on the physicochemical properties of excessive sludge, the optimal hydrothermal conditions were identified at solid-liquid ratio of 10% at 200 ℃ after 1hour of hydrothermal treatment. Under these conditions, the best sludge pretreatment effect could be obtained, and the maximum CODCr
dissolution ratio thus reached.