The industrialisation of photofermentative biohydrogen production (PFHP) using purple non-sulfur bacteria (PNSB) is constrained by inefficient light harvesting and suboptimal photon utilisation. This study systematically investigated narrow-bandwidth monochromatic single-stimulated wavelength light (SSWL) across the ultraviolet–infrared (UV–IR) spectrum to enhance light capture and biohydrogen conversion in Rhodopseudomonas palustris. Compared with white light, SSWL at 520, 810, and 850 nm significantly increased biomass accumulation by 53. 83%, 47. 65%, and 40. 00%, respectively. Irradiation at these wavelengths also enhanced fructose-1, 6-bisphosphatase activity, reaching 1072, 1047, and 978. 94 μg g⁻¹ biomass, respectively, compared with 897 μg g⁻¹ under the control spectrum. The highest accumulated biohydrogen volume (28 mL) was obtained at 520 nm, followed by 810 nm (26. 02 mL) and 850 nm (23. 33 mL). Enhanced hydrogen production at wavelengths above 500 nm correlated with increased photopigment synthesis, biomass assimilation, and dehydrogenase activity, which improved by 55. 6%, 44. 4%, and 36. 8% at 520, 810, and 850 nm, respectively. Microbial community analysis further demonstrated wavelength-dependent shifts in microbial structure, with Firmicutes, Bacteroidetes, and Proteobacteria dominating across all bioreactors (99–99. 80% relative abundance). Enrichment of Clostridiumₛensuₛtricto groups (1, 12, 13, 14, and 15) ranged from 60% to 82% under SSWL conditions. Mass and energy balance analysis revealed a significant reduction in energy requirements, with the lowest values observed at 520 nm (135 J mol⁻¹ H₂), followed by 810 nm (154. 27 J mol⁻¹ H₂) and 850 nm (162. 02 J mol⁻¹ H₂), compared with 1048. 03 J mol⁻¹ H₂ for an incandescent light source. These findings identify 520, 810, and 850 nm as optimal wavelengths for enhancing PNSB growth and PFHP, providing mechanistic insights into wavelength-engineered metabolic regulation and establishing a foundation for the development of energy-efficient, scalable photobioreactor systems.
Usman et al. (Sun,) studied this question.