Abstract: Sludge is rich in a large number of organic matters, and with the action of microorganisms, organic matter can be gradually decomposed by humic acid. Meanwhile, humic acid affects not only the degradation of organic matter but also the sludge solidification. Thus, the sludge is immersed in a constant alkaline buffer solution environment (pH=9.0). The results show that the alkaline buffer solution can accelerate the decomposition of organic matter, consume humic acid and keep the solution alkaline. When the decomposition of organic matter is completed, humic acid is released, and the degradation process continues to approximate 28 days. By adding cement and lime solidified silt, it is found that the strength of solidified silt containing organic matter increases firstly and then decrease with curing time, but the strength of solidified silt containing pre-degraded organic matter does not decrease. It indicates that the durability of solidified soil can be improved by pre-degradation of silt organic matter by the alkaline buffer solution.

Key words: sludge, humic acid, pH value, organic matter content, long-term performance