Study On Hydrogen Production By PHL Transformation With Immobilized Photosynthetic Bacteria Coupled With Metal Nanoparticles

With the increasing demand for dissolving pulp,the large amount of hemicellulose and organic matter in the pre-hydrolyzed liquor(PHL)that can be used with high value has attracted wide attention from researchers,which produced in the pre-hydrolysis treatment section of the pre-hydrolyzed kraft(PHK)dissolving pulp.Bio-photofermentation has been proven to have good application in wastewater treatment,biological hydrogen production and other fields.At the same time,nanoparticles have also attracted attention in wastewater treatment and fermentation hydrogen production due to their large specific surface area and small size effect.Therefore,this project combines bio-photofermentation with nanomaterials,and utilizes the wide adaptability of photosynthetic bacteria to simultaneously metabolize xylose and acetic acid in PHL and produce hydrogen at the same time.The large specific surface area and small size effects of nanomaterials are used to improve and increase the efficiency of photo-fermentation hydrogen production and substrate utilization.Finally,a suitable immobilized carrier was chosen to construct Fe3O4-NPs@HY01 composite microspheres,so as to improve the performance of hydrogen production and relieve the inhibitory effect to the bacteria,while also facilitating the reusage of the bacteria.Firstly,the optimal hydrogen production conditions for photosynthetic bacteria using xylose were explored.The results show that the optimal hydrogen production conditions when Rhodobacter sphaeroides HY01 uses xylose as the carbon source were as follows:the bacterial inoculum was 10%,the xylose concentration was 8 g/L,the initial pH of the solution was 8,L-glutamic acid concentration was 8.5 mmol/L,and the cumulative hydrogen production was 4227.6 mL/L.The order of various influencing factor was as follows:initial pH>L-glutamic acid concentration>inoculation amount.Secondly,photo-fermentation of H2 production can promote electron transfer and increase the activity of nitrogenase via the addition of nanoparticles,thereby increasing H2 production and substrate utilization.Different metal ions and nano-metal particles were added to the H2 production culture system to explore their influence on the H2 production of HY01.The experimental results showed that when the concentrations of Fe3+,Fe2+,Zn2+and Mg2+were≤200 mg/L,≤15 mg/L,≤350 mg/L and ≤800 mg/L,respectively,the H2 production of HY01 can be increased to various degrees.Even a small amount of addition of nano-metal particles could achieve obvious promotion effect.When the addition amount of Fe3O4-NPs,ZnO-NPs and MgO-NPs were≤200 mg/L,≤50 mg/L and≤200 mg/L,respectively,the cumulative H2 production were 4700 mL/L,4483 mL/L and 4624 mL/L,respectively.Fe3O4-NPs were selected for later experiments.Then,the effects of phenol and acetic acid on the growth,metabolism and hydrogen production of photosynthetic bacteria HY01 were investigated.The H2 production metabolism of photosynthetic bacteria when xylose-phenol and xylose-acetic acid were used as the composite carbon source were also explored.The results showed that low-concentration phenol had a certain promotion effect on the growth and hydrogen production of photosynthetic bacteria.The final tolerance threshold of HY01 to phenol was 500 mg/L.Small molecule acids could be directly transformed and utilized by photosynthetic bacteria.When xylose and acetic acid were used as dual carbon sources,the self-regulated stability of pH in hydrogen production system was improved,and the hydrogen production time was extended to 144 h,and the cumulative H2 production can reach 7200 mL/L.According to the ratio of xylose,acetic acid and phenol in PHL,a simulated pre-hydrolyzed solution was prepared to carry out the hydrogen production degradation experiment,and the cumulative hydrogen production of which was 6520 mL/L.The hydrogen production was 1.8 times higher compared that with xylose-phenol as the carbon source.Afterwards,CAD-40 macroporous resin was used to relieve the inhibitory effect of phenol,and could form a dynamic balance between the rapid adsorption and biodegradation,which facilitate HY01 to convert PHL quickly and efficiently to produce hydrogen,while it be capable of enhancing tolerance of HY01 to phenol.Finally,three biological macromolecular materials,sodium alginate,agar,and carrageenan were selected as bacteria immobilization carriers,and the light transmittance and chemical stability of these natural polymer materials and their composites were investigated.The best immobilization embedding carrier was selected,and the immobilization conditions were optimized with factors such as the amount of inoculation,immobilization time,cross-linking agent concentration and ratio.The results showed that the agar-carrageenan hybrid gel was the best immobilization carrier for HY01;the inoculation volume was 40 mL,the immobilization time was 60 min,the KCl concentration was 2%,and the agar and carrageenan were 2%,respectively.Then agar-carrageenan hybrid gel was used as the immobilization carrier to construct immobilized Fe3O4-NPs@HY01 microspheres.Experiments were conducted with simulated PHL as the fermentation substrate to analyze the hydrogen production performance,carbon source utilization capacity,tolerance of toxic substances and the recyclability of the immobilized bacterial microspheres.The utilization rate of xylose in PHL by immobilized microspheres could reach 99.45%,and the degradation rate of phenol was 28.52%,which could be recycled for six times.Through analysis and comparison,the immobilized microspheres were finally preserved by vacuum refrigeration.