Formation mechanism of persistent free radicals during pyrolysis of Fenton-conditioned sewage sludge: Influence of NOM and iron

Zhen Li; Sijing Chen; Lu Liu; Dingkang Qian; Mengjiao Yuan; Jie Yu; Zhuqi Chen; Jiakuan Yang; Xintai Su; Jingping Hu; Huijie Hou

doi:10.1016/j.watres.2024.121376

Formation mechanism of persistent free radicals during pyrolysis of Fenton-conditioned sewage sludge: Influence of NOM and iron

Water Res. 2024 May 1:254:121376. doi: 10.1016/j.watres.2024.121376. Epub 2024 Feb 29.

Authors

Zhen Li¹, Sijing Chen¹, Lu Liu¹, Dingkang Qian¹, Mengjiao Yuan¹, Jie Yu², Zhuqi Chen³, Jiakuan Yang⁴, Xintai Su⁵, Jingping Hu⁶, Huijie Hou⁷

Affiliations

¹ School of Environmental Science and Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, PR China; Hubei Provincial Engineering Laboratory of Solid Waste Treatment, Disposal and Recycling, Wuhan 430074, PR China.
² State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology (HUST), Wuhan 430074, PR China.
³ School of Environmental Science and Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, PR China; School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, PR China.
⁴ School of Environmental Science and Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, PR China; Hubei Provincial Engineering Laboratory of Solid Waste Treatment, Disposal and Recycling, Wuhan 430074, PR China; State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology (HUST), Wuhan 430074, PR China.
⁵ School of Environment and Energy, Guangdong Provincial Key Laboratory of Solid Wastes Pollution Control and Recycling, South China University of Technology, Guangzhou, Guangdong 510006, PR China.
⁶ School of Environmental Science and Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, PR China; Hubei Provincial Engineering Laboratory of Solid Waste Treatment, Disposal and Recycling, Wuhan 430074, PR China; State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology (HUST), Wuhan 430074, PR China. Electronic address: hujp@hust.edu.cn.
⁷ School of Environmental Science and Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, PR China; Hubei Provincial Engineering Laboratory of Solid Waste Treatment, Disposal and Recycling, Wuhan 430074, PR China. Electronic address: houhuijie@hust.edu.cn.

PMID: 38489852
DOI: 10.1016/j.watres.2024.121376

Abstract

The present study provided an innovative insight into the formation mechanism of persistent free radicals (PFRs) during the pyrolysis of Fenton-conditioned sludge. Fenton conditioners simultaneously improve the dewatering performance of sewage sludge and catalyze the pyrolysis of sewage sludge for the formation of PFRs. In this process, PFRs with a total number of spins of 9.533×10¹⁹ spins/g DS could be generated by pyrolysis of Fenton-conditioned sludge at 400°C. The direct thermal decomposition of natural organic matter (NOM) fractions contributed to the formation of carbon-centered radicals, while the Maillard reaction produced phenols precursors. Additionally, the reaction between aromatic proteins and iron played a crucial role in the formation of phenoxyl or semiquinone-type radicals. Kinetics analysis using discrete distributed activation energy model (DAEM) demonstrated that the average activation energy for pyrolysis was reduced from 178.28 kJ/mol for raw sludge to 164.53 KJ/mol for Fenton conditioned sludge. The reaction factor (f_i) indicated that the primary reaction in Fenton-conditioned sludge comprised of 27 parallel first-order reactions, resulting from pyrolysis cleavage of the NOM fractions, the Maillard reaction, and iron catalysis. These findings are significant for understanding the formation process of PFRs from NOM in Fenton-conditioned sludge and provide valuable insight for controlling PFRs formation in practical applications.

Keywords: Biochar; Fenton; Natural organic matter; Persistent free radicals; Pyrolysis; Sewage sludge.

MeSH terms

Carbon
Iron*
Kinetics
Pyrolysis
Sewage*

Substances

Iron
Sewage
Carbon