Utilization of soda residue and ground granulated blast furnace slag to stabilize/solidify sewage sludge in leachate soaking environment

Abstract

This study investigated sewage sludge stabilized/solidified with soda residue (SR) and ground granulated blast furnace slag (GGBS) after being dewatered with quicklime. The soaking durability test was conducted on the solidified sludge in tap water or landfill leachate. The toxicity and mineralogical characteristics of the solidified sludge were evaluated. The results showed that the unconfined compressive strength (UCS) of the solidified sludge met the strength requirement for use as a temporary cover material (≥ 50 kPa) for a short time (< 7 d). The solidified sludge had considerable soaking durability because UCS increased with the soaking time. The increase in the GGBS dosage improved the soaking durability of the solidified sludge. The UCS values of sludge solidified with 50% SR and 30% GGBS (sample S5G3) and with 80% SR (sample S8G0) after soaking in leachate for 60 d were 712.9 and 82.6 kPa, respectively. The X-ray diffraction (XRD) analysis indicated that hydration products, such as ettringite, Friedel's salt, gismondine, brushite, and hydrocalumite, contributed to the strength, soaking durability, and leachability performance of the solidified sludge. The inhibition of some hydration reactions and precipitation of ettringite and calcite on the surface of the specimens soaked in leachate led to a lower strength than that soaked in tap water. Sample S5G3 has the potential to be used as a filling or construction material, and sample S8G0 is suitable to be used as a temporary cover material in landfill.