Unveiling the mechanisms of medium-chain fatty acid production from waste activated sludge alkaline fermentation liquor through physiological, thermodynamic and metagenomic investigations

Shu-Lin Wu; Jing Sun; Xueming Chen; Wei Wei; Lan Song; Xiaohu Dai; Bing-Jie Ni

doi:10.1016/j.watres.2019.115218

Unveiling the mechanisms of medium-chain fatty acid production from waste activated sludge alkaline fermentation liquor through physiological, thermodynamic and metagenomic investigations

Water Res. 2020 Feb 1:169:115218. doi: 10.1016/j.watres.2019.115218. Epub 2019 Oct 22.

Authors

Shu-Lin Wu¹, Jing Sun², Xueming Chen³, Wei Wei¹, Lan Song⁴, Xiaohu Dai⁵, Bing-Jie Ni⁶

Affiliations

¹ State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China.
² State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, PR China. Electronic address: jingsun@tongji.edu.cn.
³ Process and Systems Engineering Center (PROSYS), Department of Chemical and Biochemical Engineering, Technical University of Denmark, 2800, Kgs. Lyngby, Denmark.
⁴ School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, PR China; Shenzhen Institute of Sustainable Development, Shenzhen, 518055, PR China.
⁵ State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, PR China.
⁶ State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, PR China. Electronic address: bjni@tongji.edu.cn.

PMID: 31677435
DOI: 10.1016/j.watres.2019.115218

Abstract

Effective sludge treatment with bioenergy production is attracting increasing interests as large quantities of waste activated sludge (WAS) are produced during the wastewater treatment. In this study, a new biotechnical process for converting the WAS alkaline fermentation liquor (WASAFL) into valuable, easy-separated medium chain fatty acids (MCFAs) through chain elongation (CE) was investigated, which may provide a new insight into sludge treatment. In the process, ethanol was served as the electron donor (EDs) and WASAFL were main electron acceptors (EAs). The MCFAs productions were investigated under three different ED to EA ratios (i.e., 1:2, 1:1 and 2:1). The result showed that MCFAs production was increased from 2.88 ± 0.01 to 5.28 ± 0.18 g COD/L with the increase of ED to EA ratio. However, the highest MCFA selectivity was achieved at 72.9% when the ED to EA ratio was 1:1. The decrease in the selectivity at high ED:EA ratio is mainly due to the production of higher alcohol (i.e., n-butanol and n-hexanol). The thermodynamic analysis confirmed all CE processes for MCFAs production from WASAFL were exothermic reactions, with the spontaneity and energy release of the reactions increased with the ethanol level. The microbial community analysis showed that the relative abundances of Clostridium, Oscillibacter, Leptolinea and Exilispira were positively correlated with the MCFAs production. The metagenomic analysis suggested that both the reverse β-oxidization pathway and fatty acid biosynthesis pathway contributed to the CE process in the studied system. The functional enzymes were mainly associated within Clostridium, with Clostridium Kluyveri, Clostridium botulinum and Clostridium magnum being likely the key species responsible for the CE process.

Keywords: Alkaline fermentation liquor; Fatty acid biosynthesis; Medium chain fatty acids; Metagenomics; Reverse β-oxidization; Waste activated sludge.

MeSH terms

Fatty Acids*
Fatty Acids, Volatile
Fermentation
Hydrogen-Ion Concentration
Sewage*
Thermodynamics
Wastewater

Substances

Fatty Acids
Fatty Acids, Volatile
Sewage
Waste Water