The neglected effects of polysaccharide transformation on sludge humification during anaerobic digestion with thermal hydrolysis pretreatment

Jun Gao; Lei Li; Shijie Yuan; Sisi Chen; Bin Dong

doi:10.1016/j.watres.2022.119249

The neglected effects of polysaccharide transformation on sludge humification during anaerobic digestion with thermal hydrolysis pretreatment

Water Res. 2022 Nov 1:226:119249. doi: 10.1016/j.watres.2022.119249. Epub 2022 Oct 14.

Authors

Jun Gao¹, Lei Li¹, Shijie Yuan¹, Sisi Chen², Bin Dong³

Affiliations

¹ State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
² State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China. Electronic address: chensisi@tongji.edu.cn.
³ State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China. Electronic address: dongbin@tongji.edu.cn.

PMID: 36323201
DOI: 10.1016/j.watres.2022.119249

Abstract

Humus accumulation during sludge stabilization is attracting increasing attention because of its land use potential. This study investigated the effects of thermal hydrolysis pretreatment (THP) on sludge humification and the related regulatory mechanisms during anaerobic digestion (AD). The sludge subjected to AD with THP at 160 °C (AnD-160) exhibited 7.3% and 8.5% higher total extractable carbon (TEC) and humic acid carbon (HAC) concentrations than the unpretreated sludge, respectively, while the sludge subjected to AD with THP at 180 °C (AnD-180) exhibited 1.4% and 7.0% lower concentrations. Humification of AnD-160 and AnD-180 were enhanced and inhibited, respectively. THP influenced sludge humification during AD through both intracellular polyphenol synthesis and extracellular humus condensation pathways related to polysaccharide metabolism. The 160 °C-pretreated sludge exhibited higher polysaccharide availability (more soluble polysaccharides and reducing sugars) than the other samples and thus had more active intracellular polyphenol metabolism during AD. The polyphenol accumulation stimulated the synthesis of related condensation enzymes (polyphenol oxidase and quinone oxidoreductases), facilitating extracellular HA production during AD. However, THP at 180 °C resulted in the highest production of melanoidins with CO-C heterocycles through C = O and CH sites of polysaccharides (778.46 vs. 193.87 R.U. nm²-mL/g for the unpretreated sample). This heterocyclization decreased the polysaccharide availability and inhibited intracellular polyphenol synthesis, consequently inhibiting condensation enzymes supply and extracellular HA production during AD. Overall, this study highlights the crucial but neglected role of polysaccharides in sludge humification during AD: the availability of polysaccharides affected by their occurrence state and molecular structure could determine the humification, which can be regulated by THP at different temperature.

Keywords: Anaerobic conversion; Humification; Polysaccharide transformation; Sewage sludge; Thermal hydrolysis.

MeSH terms

Anaerobiosis
Carbon
Hydrolysis
Methane
Polyphenols*
Polysaccharides
Sewage*
Soil
Waste Disposal, Fluid / methods

Substances

Sewage
Polyphenols
Polysaccharides
Carbon
Soil
Methane