Comprehensive insight into synergistic enhancement of nickel and iron doped lanthanum manganese oxide for biohydrogen production via anaerobic fermentation

Anaerobic fermentation offers an effective strategy to produce H2 from organic wastes, which facilitates waste utilization and the development of sustainable energy. However, the low hydrogen yield and instability of fermentation systems block the further industrial and commercial application. In this work, nickel and iron doped lanthanum manganese oxide nanoparticles (NPs) are successfully fabricated for researching their effects on H2 production and process stability. The advantages of lanthanum manganese oxides doped by nickel and iron in terms of bacterial activity and microbial community structures are studied in a fermentation system. The physicochemical properties of LaMn0.7Fe0.3O3 NPs and LaMn0.7Ni0.3O3 NPs are summarized and analyzed. The results show that the moderate addition of nanoparticles can both effectively increase the final H2 yield and stabilize the fermentation process simultaneously. The highest H2 yield of 223.08 mL/g and 246.10 mL/g correspond to 100 mg/L supplementation of LaMn0.7Fe0.3O3 NPs and LaMn0.7Ni0.3O3 NPs, respectively, which confirms that the LaMn0.7Ni0.3O3 NPs exhibit a more positive impact on anaerobic fermentation, while excess dosage nanoparticles (over 100 mg/L) may hamper the H2 production and inhibit the electron transfer to microbe. The underlying mechanism analysis reveals that Fe3+ and Ni2+ significantly improve the microbial transmembrane transportation and conversion rate of glucose into acetate, butyrate and H2 through stimulating the activity of related enzymes, leading to an enhanced H2 productivity. Meanwhile, Ni2+ and Fe3+ are helpful to the synthesis of ferredoxin and hydrogenase, which increase the activity of critical enzymes. The microbial community discloses that LaMn0.7Fe0.3O3 NPs and LaMn0.7Ni0.3O3 NPs separately make a 7.71%, 9.65% increase of Clostridium_sensu_stricto_1 compared to the control group, which is deeply involved in the sustainable H2 generation. Based on comprehensive evaluation, LaMn0.7Ni0.3O3 NPs will have a huge potential market for H2 production enhancement in anaerobic fermentation system.