Effects of He-Ne red and green laser irradiation on purple non-sulfur bacteria for biohydrogen production from food wastes

Light saturation of photo-fermentation is an important parameter that impacts fermentation efficiency, especially in mass culture. In other words, unsteady light irradiation negatively affects biohydrogen production. In this study, it is hypothesized that hydrogen-producing bacteria exposure to laser irradiation will improve the survival competence of bacteria to unstable illumination, overcome the challenge of light saturation, and increase biohydrogen production. The experimental design can be summarized as follows: exposing the bacterial inoculum to helium-neon (He-Ne) red or green laser for 2 h, and subsequently blending the inoculum with food wastes in addition to water through the ratio 0.5:1:2 and adding the mixture to photobioreactors irradiated with white light-emitting diodes (LEDs) with a luminous flux of 3600 lm and at 30 degrees C for 26 days with mixing for 5 min every 30 min to produce biohydrogen. The results indicated that an improvement in the bioresponses of bacterial cells which increased the biohydrogen yield by 1.79 and 1.2 times the control (un-irradiated inoculum) when using He-Ne green and red laser irradiation, respectively. The green laser activation for bacterial inoculum showed the maximum H-2 yield of 25.4 mol H-2 mol/mol sugar. However, the inoculum with red laser irradiation delivered 15.2 mol H-2 mol/mol sugar. The least H-2 yield of 12.0 mol H-2 mol/mol sugar was attained by the control. The contribution of this research to the field is that developing a novel technology for maximizing the generation of biohydrogen from biomass through the photobiostimulation of hydrogen-producing bacteria using laser irradiation.