Steam explosion coupled with freeze-thaw cycles: An efficient and environmentally friendly method for deep dewatering of sewage sludge

The high moisture content of municipal sewage sludge (MSS) is one of the most critical barriers restricting its subsequent utilization. This work proposed a new method named steam explosion (SE) coupled freeze-thaw (F-T) for enhancing the deep dewatering of MSS. The influence of SE pressure, SE holding time, and freezing tem-perature on sludge dewatering performance and changes in the physical structure and chemical composition of sludge flocs were investigated. The moisture content of the sludge cake was reduced to 30.67 +/- 0.42 % under conditions of SE pressure of 2.4 MPa, SE time of 30 min, and freezing temperature of-5 degrees C after mechanical filtration. The SEM and particle size analysis results showed that steam explosion pretreatment could effectively break the sludge gel-like structure, and the resulting small sludge particles flocculated by subsequent freeze --thaw treatment. The TOC, 3D-EEM, FT-IR, XPS and other analysis results revealed that SE/F-T was conducive to decomposing sludge extracellular polymer substances (EPS) and transforming and accumulating organic matter to the outer layer of EPS. Additionally, the content distribution, speciation transformation, and leachability of heavy metals in sludge cakes were analyzed to evaluate the potential environmental risks of sludge samples. This study provided an efficient and environmentally friendly method for strengthening the dewatering performance of MSS and helped lay a theoretical foundation for the practical application of SE/F-T technology in sludge treatment.

Automated summary

This study proposed a new method named steam explosion (SE) coupled freeze-thaw (F-T) for enhancing the deep dewatering of municipal sewage sludge (MSS). The results showed that SE/F-T could effectively break the sludge gel-like structure and flocculate small sludge particles. The analysis also revealed that SE/F-T was conducive to decomposing extracellular polymer substances (EPS) and transforming and accumulating organic matter in sludge.