Revealing the Mechanism of Biochar Enhancing the Production of Medium Chain Fatty Acids from Waste Activated Sludge Alkaline Fermentation Liquor

Abstract

In this work, the effectiveness of biochar with distinctively different particle sizes (i.e., 2000−5000 and 75−150 μm) derived from anaerobically digested sludge was comprehensively evaluated in the production of enhancing MCFAs (medium chain fatty acids) using waste activated sludge alkaline fermentation liquor as feedstock with ethanol as the electron donor. The results showed that fine biochar (i.e., 75−150 μm) was more favorable for enhancing the production of MCFAs with an increased electron transfer efficiency reaching 92.6%. Metagenomic analysis revealed that the total microbial taxonomic composition shifted in favor of the production of MCFAs (e.g., Clostridium kluyveri sp., Clostridium magnum sp., and Clostridium botulinum sp.). The increased relative abundance of functional enzymes associated with the production of MCFAs confirmed that both the reverse β-oxidation pathway and the fatty acid biosynthesis pathway were enhanced by biochar. Mechanistic studies revealed that the biochar had high redoxactive properties due to the functional groups (mainly quinones and hydroquinone) on its surface and an important ability to charge and/or discharge, which thus promoted the transfer of electrons for the production of MCFAs during the CE process.

Performance and Mechanism of Fe3O4 Improving Biotransformation of Waste Activated Sludge into Liquid High-Value Products

“…For example, the abundances of Firmicutes and Actinobacteriota in the 5 g/L Fe 3 O 4 group increased by 11.41 and 1.35%, as compared with those in the control group, respectively. Firmicutes was reported frequently as the dominant phylum in WAS fermentation for MCFA production . Wang et al and Wu et al reported that the abundance of Firmicutes was positive with MCFAs produced from WAS. , Consequently, Fe 3 O 4 addition increased the populations of CE-related microorganisms, which may contribute to MCFA production.…”

“…Organic matters mainly existed in the solid phase of WAS . In the solubilization process, WAS was disintegrated, accompanied by releasing organic matters into the liquid phase . Therefore, the extent of WAS solubilization could be reflected by the changes of soluble organic matters.…”

“…28 In the solubilization process, WAS was disintegrated, accompanied by releasing organic matters into the liquid phase. 29 Therefore, the extent of WAS solubilization could be reflected by the changes of soluble organic matters. Figure 2a represents the concentration of soluble protein and polysaccharides after 1 day of fermentation in each group.…”

“…Firmicutes was reported frequently as the dominant phylum in WAS fermentation for MCFA production. 29 Wang et al and Wu et al reported that the abundance of Firmicutes was positive with MCFAs produced from WAS. 11,31 Consequently, Fe 3 O 4 addition increased the populations of CE-related microorganisms, which may contribute to MCFA production.…”

Transformation of Antimonate at the Biochar–Solution Interface

“…Biochar is recognized as black carbon, , which has four characteristic XPS spectra of C 1s components (CC, CO, CO, and COOH/COOR) in the ranges 284.3–284.8 (C 1s A), 285.4–286.4 (C 1s B), 286.8–287.8 (C 1s C), and 288.9–289.4 eV (C 1s D), respectively (Figure S3). − The main CC chain (sp 3 C) that represents amorphous carbon and other three oxygen-containing groups such as CO, CO, and COOH/COOR were produced due to the bonding of oxygen to incomplete C-bonds during synthesis. The FTIR data also confirmed these groups in CMBC and HMBC.…”