Influence of organic matter type and content on the intrinsic compressive behavior of sewage sludge

• For high-active organic soils, physical and compression indices rise with organic content, while they decline for low-active ones. • The above‑mentioned parameters of low‑activity soils are positively correlated with particles smaller than 10 μm; in both types of soils, specific gravity decreases with increasing organic matter content. • When vertical effective stress exceeds 100 kPa, the compression curves of the two organic soils can be normalized to the same ICL: I v =0.103(log σ ' v ) 2 -1.499(log σ ' v )+2.566, with a correlation coefficient of 0.99. • Microscopic mechanism is verified by SEM. The compressibility of municipal sewage sludge is significantly influenced by its type and content of organic matter. This study investigated the impact of organic matter type and dosage on sludge compressibility. To this end, raw sludge was mixed with different amounts of dry soil powder and humus to prepare two types of organic soil specimens. These specimens were subjected to a series of tests, including Atterberg limits, specific gravity, particle size analysis, and one-dimensional confined compression tests. For organic soils with organic content ranging from 15% to 65%, the results indicate that the sludge-dry soil powder organic soil exhibits high activity, whereas the sludge-humus organic soil shows low activity. For high-activity organic soils, parameters such as liquid limit, plastic limit, plasticity index, compression coefficient, compression index, and intrinsic compression parameters exhibited an increasing trend with increasing organic content. Conversely, these parameters exhibited a decreasing trend for low-activity organic soils. The specific gravity of both organic soils decreases linearly with increasing organic content. For low-activity organic soils, the compression parameters show a strong correlation with the content of particles smaller than 10 μm. The average intrinsic compression line (ICL) for the two types of organic soil was plotted, revealing that their compression curves were highly comparable and lay on the same ICL under vertical effective stress greater than 100 kPa. This study provides a comprehensive overview of the theoretical and practical aspects of sludge disposal, resource recovery and leachate assessment.