Optimization Of Photo-fermentation Biohydrogen Production Process By Co-digestion Of Corn Straw And Duckweed

Under the framework of renewable and sustainable energy technology,biohydrogen production is considered as the most attractive alternative to energy production.Two or more complementary substrates are mixed to produce hydrogen,which can improve the nutrient balance of fermentation system,promote the synergistic effect on hydrogen producing microorganisms and improve the substrate conversion rate.The photosynthetic bacteria HAU-M1 was used as hydrogen producing bacteria,duckweed and corn straw were used as co-fermentation substrates,and hydrogen yield(HY)was used as evaluation index to study the optimal mixing ratio.The process conditions affecting co-fermentation photosynthetic hydrogen production(CFPHP)were optimized.In the whole experiment,firstly,the physical parameters of duckweed and corn straw were determined to explore the feasibility of co-fermentation of duckweed and corn straw for hydrogen production;secondly,the types and loads of enzymes used in duckweed enzymatic hydrolysis for hydrogen production were screened and optimized;thirdly,based on the results of single factor experiment,Plackett Burman experiment was used to screen out the significant factors affecting the CFPHP,and the response surface CCD experiment was used to optimize the CFPHP conditions.Finally,HY,hydrogen production rate(HPR),hydrogen concentration,pH value of fermentation broth,reducing sugar concentration,volatility of small molecular acids(VFAs)and ethanol were determined and analyzed.The results showed that:(1)The HY of duckweed using cellulase and amylase under different enzyme loads was significantly different(p<0.05),but there was no significant difference under different protease loads(p>0.05).The results of response surface methodology CCD showed that there was no synergism between cellulase and amylase.Therefore,the maximum HY of 63.40 mL/g TS was obtained by using cellulase from duckweed at 200 mg/g.(2)When the ratio of duckweed to corn straw was 5:1,the ratio of carbon to nitrogen(C/N)was 13.2,and the maximum HY was 78.0 mL/g TS,which was 24.0%and 36.04%higher than that of duckweed and corn straw,respectively.The results showed that the C/N could be controlled in an appropriate range by adjusting the mixture ratio of materials,which was conducive to the multiplication of PSB and the degradation of organic matter in fermentation broth.producing ATP for hydrogen production and metabolism growth of PSB.(3)On the basis of 5:1 ratio of duckweed and corn straw,the single factor optimization experiment was carried out.The results showed that the optimal conditions for hydrogen production by co-fermentation were as follows:substrate concentration 35 g/L,initial pH 8,inoculation volume ratio(IVR)20%(v/v),temperature 30?,light intensity 3000 Lux.According to the results of PB experiment,the effect of temperature on HY was more significant(p<0.0001),followed by substrate concentration,initial pH and inoculation volume ratio(p<0.05),while light intensity(p=0.5828>0.05)had no significant effect on hydrogen production.(4)The results of response surface methodology CCD experiment showed that the effect of substrate concentration and initial pH was significant(p<0.0001),followed by the interaction between temperature and IVR,and the interaction between temperature and substrate concentration was not significant(p=0.0675>0.05).The optimum conditions of hydrogen production were as follows:substrate concentration 37.89 g/L,temperature 30.98?,initial pH 7.81 and IVR 28.78%.Under these conditions,the maximum HY was 95.10 mL/g TS,which was 2.38%compared with the predicted value of the model equation.According to the kinetic parameters fitted by the modified Gompertz equation,the highest HPR was 5.05 mL/g TS/h,the highest HPR occurred at 18.52 h,and the hydrogen production delay time was 11.36 h,which was also consistent with the phenomenon of hydrogen production process.Under the optimum conditions,the energy conversion is 7.16%.The pH value of hydrogen production liquid decreased rapidly in the initial stage.With the process of reverse fermentation,the pH value in the fermentation liquid decreased slowly,then rose slightly and maintained in a state of dynamic equilibrium.The results of liquid phase analysis showed that the mode of CFPHP was mixed acid fermentation,and the concentration of acetic acid and butyric acid in VFAs was much higher than that of propionic acid.