Strength and Leachability of Solidified Sewage Sludge with Different Additives: Fid-Bau Portal

Strength and Leachability of Solidified Sewage Sludge with Different Additives

Lin, Cheng / Zhu, Wei / Han, Jie

Production and disposal of sewage sludge have raised increasing concerns due to their poor mechanical properties and negative environmental effect. Cement-based solidification/stabilization can improve the properties of sewage sludge so that it can be used either as an earth-construction material or landfills. To achieve this goal, a large amount of cement should be used, thus increasing the treatment cost and ${CO}_{2}$ emission arising from cement production. To reduce cement usage, three inorganic additives (e.g., calcium-bentonite, fly ash, and kaolinite) were used and investigated in this study to improve the effectiveness of solidification/stabilization of sewage sludge with cement. The benefits of these additives to the treated sewage sludge were evaluated in terms of unconfined compressive strength and leaching of pollutants including alkalinity, chemical oxygen demand (COD), and heavy metals (e.g., copper, lead, and zinc). X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) were conducted to examine the mechanisms associated with the behavior of the treated sludge resulting from these additives. The test results show that calcium-bentonite was a favorable additive to improve the effectiveness of cement to solidify/stabilize the sewage sludge. As the ratio of sewage sludge, and cement, to calcium-bentonite by weight reached 1:0.2:0.2, the unconfined compressive strength of the treated sewage sludge could meet the requirement for landfilling at seven days and that of a construction material at 28 days.