Co-hydrothermal carbonization of sludge and food waste for hydrochar valorization: Effect of mutual interaction on sulfur transformation

Zhenqi Wang; Jingchun Huang; Junwen Wang; Zhen Hu; Minghou Xu; Yu Qiao

doi:10.1016/j.scitotenv.2023.167318

Co-hydrothermal carbonization of sludge and food waste for hydrochar valorization: Effect of mutual interaction on sulfur transformation

Sci Total Environ. 2023 Dec 20:905:167318. doi: 10.1016/j.scitotenv.2023.167318. Epub 2023 Sep 24.

Authors

Zhenqi Wang¹, Jingchun Huang², Junwen Wang¹, Zhen Hu¹, Minghou Xu¹, Yu Qiao¹

Affiliations

¹ State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan 430074, China.
² State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan 430074, China. Electronic address: hjccxc@hust.edu.cn.

PMID: 37742985
DOI: 10.1016/j.scitotenv.2023.167318

Abstract

Co-hydrothermal carbonization of sludge and food waste is a promising method for hydrochar valorization. The sulfur content and form of hydrochar are the key parameters that determine its further utilization. However, the effect of the chemical composition of food waste on sulfur redistribution remains unknown. Herein, the sulfur transformation behavior during the co-hydrothermal carbonization of sludge and model compounds (cellulose, starch, xylan, and palmitic acid) of food waste was investigated, with focus on the detailed reaction pathways from inorganic-S/organic-S media in aqueous to hydrochar. The added model compounds, particularly the starch and xylan, increased the sulfur retention ratio from 41.0 to 44.7- 49.2 % in hydrochar. Among them, starch and xylan can react with aliphatic-S in aqueous via cyclization and oxidization to form the thiophene-S/aromatic-S and sulfone-S and can react with SO₄^2--S to form sulfone-S via sulfonate reaction. These formed organic-S can polymerize with hydrolyzed intermediates (i.e., 5 hydroxymethyl-furfural, glucose, and xylose) from model compounds to transform into hydrochar. Cellulose enhanced the formation of sulfone-S in hydrochar via the reactions between the water-insoluble partial hydrolysate and SO₄^2- in the aqueous. Additionally, palmitic acid hydrolysate provided an acidic environment that facilitated the polymerization of thiophene-S/aromatic-S from aqueous to hydrochar. Generally, the chemical composition of food waste largely affects the redistribution behavior of sulfur during co-hydrothermal carbonization, and this occurs primarily due to the differences in the hydrolysate and degree of hydrolysis for various model compounds. The results can provide guidance for preparing sludge-based hydrochar possessing different sulfur content and species, that can be used as clean fuel or carbon material.

Keywords: Co-hydrothermal carbonization; Food waste; Interaction; Sewage sludge; Sulfur transformation.