Role Of Surfactant In Affecting Photo-Fermentative Bio-Hydrogen Production From Corncob

Among the various measures to improve the current increasingly serious environmental pollution and energy shortage problems,bio-hydrogen production,with its combination of waste utilization,light energy conversion and energy production,can not only realize the transformation of biomass resources into high value-added products,but also improve global warming and energy shortage problems,which has become the focus of current research.Corncob is the main by-product of corn harvesting,with high cellulose content and huge yield,and is the main provider of raw materials for the photo-fermentative biohydrogen production.However,the physical barrier effect of corncob structure and the non-specific adsorption of cellulase in the photo-fermentative biohydrogen production process greatly limit its application potential.Effective means of delignification and pretreatment technologies are the key to obtain higher bioenergy yield.In this paper,the effects of surfactants on the photo-fermentative biohydrogen production of corncob were studied.The effects of surfactants(Tween 20,Tween 60,Tween 80,Rhamnolipids and Tea Saponin)on the photo-fermentative biohydrogen production system were comprehensively considered,and the best surfactant type and addition amount were selected from five surfactants with enzymatic hydrolysis characteristics and hydrogen production characteristics as evaluation indexes.Furthermore,the influence of surfactant-assisted pretreatment technology on photo-fermentative biohydrogen production system was further explored.The results show that:(1)The changes of physical and chemical properties of fermentation broth under different pretreatment parameters were examined,and the structural properties and energy analysis of corncob were also investigated.On this basis,the Box-Behnken Design(BBD)model was used to optimize the optimal process conditions.The appropriate surfactant concentration has a significant contribution to the hydrogen production performance and enzymatic hydrolysis properties,while too high or too low addition concentration has a negative effect.The effect of the addition of different types of surfactants on the increase of reducing sugar concentration at 48 h was different,which could be ranked as Rhamnoolipin>Tween 80>Tween60>tea saponin>Tween 20.When Rhamnoolipid,Tween 80,Tween 60,Tea saponin and Tween 20 were added to 0.08 g/L,0.20%(v/v),0.10%(v/v),1.50 g/L and 0.05%(v/v)respectively,the maximum cumulative hydrogen production of photosynthetic organisms was 110.16±6.07 m L,108.54±2.69 m L,104.80 ± 0.66 m L,98.45 ± 3.89 m L,85.68 ± 0.85 m L,which were 43.40%,41.29%,36.42%,28.15%,11.53% higher than blank group,respectively.The synergies of surfactants on the photo-fermentative biohydrogen production of corncob could be ranked as Rhamnoolipid > Tween 80 > Tween 60> Tea saponin> Tween 20.(2)The optimum process conditions for the photo-fermentative biohydrogen production from corn cob were as follows: microwave radiation time of 6 min,microwave radiation power of 700 W,and Rhamnolipid addition concentration of0.08 g/L.The change of the microstructure of corncob under the optimum pretreatment parameters was deeply analyzed.The Fourier transform spectroscopy showed that the location of the main absorption peaks was almost the same,but the intensity was reduced.Several significant differences of characteristic peaks were 3430 cm-1,2930 cm-1,1730 cm-1and 1040 cm-1,corresponding to O-H stretching vibration,C-H stretching vibration,C=O stretching vibration and C-O stretching vibration,respectively,which proved that the structure and content of cellulose,hemicellulose and lignin changed after pretreatment.X-ray diffraction showed that the effect of surfactant-assisted pretreatment on the amorphous region of cellulose was more significant than that on the crystalline region of cellulose,which helped to reduce the content of lignin and hemicellulose.From the scanning electron microscopy observation,it was found that the surface striations of corncob treated with surfactant-assisted pretreatment technology were destroyed,with a large number of cracks and lobes,and the overall structure was loose and fragmented,even with a pore structure on the surface,which did not have the highly ordered and rigid structure of the original corn cobs.In addition,the surfactant-assisted pretreatment technique obtained a higher specific energy ratio compared to the single microwave pretreatment technique,indicating that this technique is more valuable and efficient.(3)Based on the single-factor experimental results,the experiments were further optimized by BBD response surface model,and the optimal experimental conditions were obtained as microwave radiation time of 5.51 min,microwave radiation power of 772.03 W,and Rhamnoolipid concentration of 0.08 g/L.Under these conditions,the predicted cumulative hydrogen production was 137.75 m L.The actual cumulative hydrogen production was 135.7 m L by the validation experiment,with a relative error of only 1.49%,indicating a good fit of the model.In addition,the interaction between microwave radiation power and Rhamnoolipid addition concentration had the greatest effect on the cumulative hydrogen production by the photo-fermentative biohydrogen production from corncob,while the interaction between microwave radiation power and microwave radiation time and between microwave radiation time and surfactant addition concentration had less effect on the cumulative hydrogen production.