Effect of metals on the regulation of acidogenic metabolism enhancing biohydrogen and carboxylic acids production from brewery spent grains: Microbial dynamics and biochemical analysis

Abstract

The present study reports the mixed culture acidogenic production of biohydrogen and carboxylic acids (CA) from brewery spent grains (BSG) in the presence of high concentrations of cobalt, iron, nickel, and zinc. The metals enhanced biohydrogen output by 2.39 times along with CA biosynthesis by 1.73 times. Cobalt and iron promoted the acetate and butyrate pathways, leading to the accumulation of 5.14 gCOD/L of acetic and 11.36 gCOD/L of butyric acid. The production of solvents (ethanol + butanol) was higher with zinc (4.68 gCOD/L) and cobalt (4.45 gCOD/L). A combination of all four metals further enhanced CA accumulation to 42.98 gCOD/L, thus surpassing the benefits accrued from supplementation with individual metals. Additionally, 0.36 and 0.31 mol green ammonium were obtained from protein‐rich brewery spent grain upon supplementation with iron and cobalt, respectively. Metagenomic analysis revealed the high relative abundance of Firmicutes (>90%), of which 85.02% were Clostridium, in mixed metal‐containing reactors. Finally, a significant correlation of dehydrogenase activity with CA and biohydrogen evolution was observed upon metal addition.

Carbonic anhydrase assisted acidogenic fermentation of forest residues for low carbon hydrogen and volatile fatty acid production: enhancedin situCO2reduction and microbiological analysis

“…To enhance the productivity of caproic acid, the microbial process needs proper investigations and regulation considering the influential factors. 36,50…”

“…This finding is corroborated by the previous studies that demonstrated Clostridium sensu stricto as the primary hydrogen producer and have observed a correlation between its abundance and hydrogen yield. 36,57,58 Yang and Wang examined microbial community structure changes in dark fermentative hydrogen generation and found that Clostridium sensu stricto 1 contributed more to hydrogen production. 59 Kumar et al used experimental design to determine optimum hydrogen generation settings and discovered that Clostridium sp.…”

“…72 Likewise, other studies have made similar assumptions on volatile fatty acids production. 36,58,71 In a study conducted by De Leeuw (2019), it was observed that the presence of Caproiciproducens ASV2 in the reactor, alongside Lactobacillus rhamnosus ASV4, during the initial high level of total VFAs production resulted in a higher production of butyric and caproic acids, while the production of acetic acid was lower. This outcome is likely attributed to a chain elongation process facilitated by Caproiciproducens , utilising lactic acid generated by lactobacilli as an electron donor.…”

“…A detailed overview of the methods employed in DNA sequencing, library preparation, and bioinformatics processing has been previously described. 36…”

“…To enhance the productivity of caproic acid, the microbial process needs proper investigations and regulation considering the influential factors. 36,50 In phase II, the metabolic route was altered with respect to substrate and fermentation pH (6, 7 and 8) impacting the pattern and distribution of SCFA and MCFA. While acetic and butyric acid production was minimal across all reactors, caproic acid production was significantly influenced.…”