Activation of N2-fixing bacteria with ferric-NPs enhances biohydrogen generation from industrial wastes

Abstract

The present study compared the effects of iron nanoparticles (FeNPs) and FeCl3 on the growth, nitrogenase activity, and H2 production of mesophilic bacteria Enterobacter aerogenes and Bacillus thuringiensis. FeNPs were synthesized using the forcing-hydrolysis method of ferric chloride. The synthetic FeNPs exhibited a distinct peak in the surface plasmon resonance at 350 nm and irregularly shaped particles ranging in size from 33 nm to 50 nm. X-ray diffraction (XRD) analysis confirmed that the synthesized FeNPs matched the hematite database (JCPDS file No. 19–629). The growth of E. aerogenes and B. thuringiensis was significantly higher in the presence of FeNPs than in the presence of FeCl3. The highest growth rate was observed at an FeNP concentration of 150 mg/L. Nitrogenase activity in both E. aerogenes (2.6-fold increase) and B. thuringiensis (2.4-fold increase) was higher when FeNPs were present compared to control cultures without iron addition. The study also investigated the effects of FeCl3 and FeNPs on H2 generation by Enterobacter and Bacillus using orange peel hydrolysate and molasses as substrates. The results showed that Supplementation of 6% orange peel hydrolysate with 150 mg/L of FeNPs significantly increased cumulative H2 generation, resulting in a yield of 1.92 mol H2/mol glucose in Enterobacter aerogenes. Similarly, in Bacillus thuringiensis, the cumulative H2 produced from 6% molasses supplemented with 150 mg/L FeNPs was 2.36 mol H2/mol glucose. These findings suggest that FeNP supplementation, rather than FeCl3 supplementation, can enhance the bioactivity of H2-producing bacteria and improve H2 yield. This has significant implications for the economic importance and feasibility of biofuel technologies that utilize industrial waste products.