Target-oriented recruitment of Clostridium to promote biohydrogen production by nano-ferrihydrite

In this study, the hydrogen production of anaerobic sludge was investigated through heat treatment and with enrichment of hydrogen-producing microorganisms in the presence of nano-ferrihydrite. Hydrogen production and hydrogen yield peaked at 0.97 mmol and 2.55 mol H-2/mol glucose in the batch experiment amended with nano-ferrihydrite. In contrast, no hydrogen was detected in the blank batch group without nano-ferrihydrite. Microbial community analysis based on 16S rRNA gene sequencing revealed that Clostridium (77.3%) and Bacillus (81.4%) were the dominant genera of the batch groups in the presence and absence of nano-ferrihydrite, respectively. In accordance with the community structure, acetate and butyrate were the primary end products in the batch group dominated by Clostridium, while lactate and ethanol were the main products in the batch group with primarily Bacillus. The carbon conversion efficiency was elevated by 265%, from 22.6% in the control group to 82.4% in treatment with nano-ferrihydrite. More importantly, the energy conversion efficiency markedly shifted from 21.5% under the control condition to 100.3% in the presence of nano-ferrihydrite. Subsequently, a bacterium named C. pasteurianum YC-1 with the ability to yield 2.61 mol H-2/mol glucose, was isolated in this study. The improved hydrogen generation can be attributed to nano-ferrihydrite being capable of shaping the microbial structure, altering metabolic pathways, and acting as released Fe(II) for hydrogenase synthesis and as a pH buffer. This study demonstrates that nano-ferrihydrite is an effective, green, and low-cost material to strengthen fermentation and biohydrogen production by the screening-oriented recruitment of Clostridium