Synergistic effects in the copyrolysis of municipal sewage sludge digestate and salix: Reaction mechanism, product characterization and char stability
2021
Wang, Shule | Mandfloen, Per | Jönsson, Pär | Yang, Weihong
Anaerobic digestion is a practical process for recovering energy and materials from sewage sludge. However, land disposal of the derived digestate results in environmental problems, such as eutrophication and salinization. Copyrolysis of sewage sludge digestate and lignocellulosic biomass produces a high-quality oil, a diluted hazardous component of biochar. This study investigates the copyrolysis behavior of lignocellulosic biomass and sludge digestate with different blending ratios using bench-scale experiments. Compared to individual feedstock pyrolysis, copyrolysis shows a higher energy distribution in the liquid product and a lower energy distribution in the char and gas product. The highest energy yield with respect to the organic fraction of liquid product is observed in the copyrolysis case, corresponding to 36.4% of the total energy in the feedstock. The interaction between the sludge digestate and lignocellulosic biomass is studied through product characterizations, mechanistic investigations and char stability assessments. The liquid products in the copyrolysis cases show a relatively high abundance of esters, aliphatic hydrocarbons, pyridines and pyrroles. The reaction pathways of proteins, lipids and carbohydrates are investigated. Two synergistic reaction pathways are proposed. The char stability and nitrogen distribution are investigated. According to the results, the synergistic interaction between feedstocks enhances the quality and energy yield of the liquid biofuel. The char product from copyrolysis has higher potential for use as a carbon sink and fertilizer.
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