In-situ reaction mechanism of vacuum pyrolysis for extracting valuable materials from waste excess biological sludge

Abstract

The large amount of biomass components contained in waste excess biological sludge make it a highly potential energy provider. The effective separation of organic and inorganic substances in waste biological sludge is crucial for the resource reuse of sludge. In this study, the vacuum pyrolysis technology has been developed to treat waste excess biological sludge. The product yields were 51.53 wt% residue, 48.47 wt% pyrolysis oil, and pyrolysis gas, respectively. Thermogravimetric analysis showed that at 10, 20, and 30 K∙min−1, the E value slightly changed from 11.02 to 12.08 kJ∙mol−1, with corresponding A values of 0.24, 0.46, and 0.74, respectively. High heating rate leads to an increase in reaction rate, but is not conducive to the effective separation of organic compounds. Based on in-situ analysis of vacuum temperature changes, FTIR and XRD indicate that organic functional groups fracture regularly, but inorganic substances do not show significant changes. XPS elemental flow analysis shows that P and S are enriched in residue after reaction, and Mg and Zn may enter the pyrolysis oil and gas. We also studied quality balance and cost evaluation. The total cost of pure air pyrolysis for 1 m3 dry sludge is approximately $143.375. In summary, the practical application of sludge vacuum pyrolysis technology still faces significant challenges, and this study provides support for improving understanding of the vacuum pyrolysis process of waste excess biological sludge.