Mechanisms of enhanced hydrogen production from sewage sludge by ferrous ion: Insights into functional genes and metabolic pathways

Hydrogen production from sewage sludge was studied in the presence of Fe2+. The results showed that the highest cumulative hydrogen production of 26 mL/100 mL was achieved with 600 mg/L Fe2+ supplementation, which was 2 times of the control test. In depth analysis of organics in liquid phase revealed that Fe2+ addition promoted sludge disintegration and protein degradation during fermentation process. Functions prediction by PICRUSt analysis indicated the effect of Fe2+ on microbial metabolism and functional genes expression. The results showed that the expression of hydrogen-producing functions, like ferredoxin hydrogenase and formate dehydrogenase was activated by Fe2+ supplementation, while the hydrogen-consuming metabolism, like methane metabolism and homoacetogenic metabolism was inhibited. Furthermore, Fe2+ addition could stimulate organics utilization. This study explored the effect of Fe2+ on functional genes abundance, revealing the mechanisms of enhanced hydrogen production by Fe2+ from the perspective of microbial metabolism.

Automated summary

The addition of Fe2+ in sewage sludge can enhance the expression of hydrogen-producing functional genes, inhibit hydrogen-consuming metabolism, and stimulate organics utilization, thereby increasing hydrogen production.