Steam-exploded Corn Stover To The Anaerobic Digestion Of High-temperature Solid-state Ladder

As a large agricultural country, the total amount of biomass resources which our country produces every year surpasses 3 billion tons; most has been represented by each kind of plant stalks. But the traditional use causes the massive surplus of stalks, the phenomenon of stalk burning is very common in each region, not only has caused the environmental pollution, but also a kind of waste of stalk resources.Presently, the unceasing increase of world population and the reduction of fossil fuel reserve have becoming the question which is avoidless, the influence of energy and resources crisis is remarkable to every country day by day. Seeking for the environmental friendly substitute for fossil fuel has become the common research hotspot in every country. Hydrogen and biogas are two kinds of representative environmental friendly renewable energy. Hydrogen and methane production by anaerobic digestion from biomass are helpful in solving the problem of surplus of massive stalks and energy crisis.The complex structure of plant stalks makes the degradation by microorganism a difficult and slow process. Therefore, the pretreatment method becomes a key factor in the process of effective use of stalk. Biogasification by submerged culture and the present physical, chemical, biological pretreatment of stalk have encountered with some key problems, such as long cycle,high energy consumption and serious pollution. Corn stalk has been used in thermophilic solid state anaerobic digestion to obtain hydrogen and biogas in different phases, in order to research a new way in high value use of biomass resources.Steam explosion is a widely used pretreatment method which in present lignocelluloses pretreatment technique, it can destroy the compact structure of stalks effectively, enhances the degradation rate of lignocelluloses. Effect on biogasification by anaerobic digestion from corn stalk at different steam explosion intensity has been researched. When steam-exploded stalk (SES) was treated at a saturated vapor pressure of 1.5 MPa for 6 min, the best result obtained showed that methane yield was 138.2ml/gTS, which was 3.5 times of that by raw stalk.With the single factor experimental optimization of solid-liquid ratio, initial pH, inoculum size, nitrogen source, cellulase addition, fermentation temperature, the optimal conditions obtained were as follows: 1:7 of solid-liquid ratio, 7.5 of initial pH, 35% of inoculum size,0.04g of NH4HCO3 addition per gram dry SES, 30IU of cellulase addition per gram dry SES and 50℃of fermentation temperature. Under the above controlled experimental conditions, the methane yield of SES was high up to 153.0ml/g TS, which was 2.9 times of that with no steam explosion pretreatment; the methane production rate of SES was 7.54ml/gVSS·d, which was 2.4 times of that with no steam explosion pretreatment. With the component determination of fermentation residual, the degradation rate of cellulose and hemicellulose after fermentation was 59.86% and 67.22%, which was 3.2 times and 3 times of that with no steam explosion pretreatment respectively.Clostridium butyricum is a kind of anaerobic Clostridiums which use some sugars, such as glucose and xylose, as favorable carbon source. It may transform the substrate into hydrogen, acetic acid, butyric acid, and enhances the hydrogen production in anaerobic digestion. Under the optimal steam explosion and fermentation conditions, SES was used in thermophilic solid state step-by-step anaerobic digestion. After inoculation of Clostridium butyricum and digestion sludge, hydrogen was obtained in the first phase. In the second phase which hydrogen production ended, biogas was obtained after pH adjusted to neutral. In step-by-step anaerobic digestion, the hydrogen yield of SES was 76.0ml/gTS,which was 2.3 times of that with raw stalk, hydrogen production rate of SES was 13.1ml/gVSS·d, which was 2.0 times of that with raw stalk; the methane yield of SES was 171.7ml/gTS, which was 2.6 times of that with raw stalk, methane production rate of SES was 7.72ml/gVSS·d, which was 2.1 times of that with raw stalk.Therefore, steam explosion pretreatment help improve the gas production of corn stalk effectively with high degradation rate in thermophilic solid state anaerobic digestion and step-by-step gasification process from corn stalk. It can be considered to be an efficient technique in high value use of biomass resources. Anaerobic digestion at thermophilic condition can eliminate some interferences of mesophilic microorganism, make the fermentation temperature according with the optimal hydrolysis temperature of cellulase to obtain an efficient degradation process, shorten the lag phase, and enhance the biogas yield and gasification efficiency. Meantime, solid state fermentation can maintain a high concentration of inoculum and nutrition, produce less waste water, which is friendly to environment.