Cogeneration Of Hydrogen And Methane From Biomass Rich In Starch/cellulose By Anaerobic Fermentation

Energy and environment are the two of the most important problems human beings meet nowadays. Hydrogen has ideal characteristics as an energy carrier, such as clean and high energy yield. Therefore, the concept of hydrogen energy has attracted worldwide interest. The feasibility of cogeneration of H2 and CH4 from biomass was investigated using glucose as a model substrate. The cogeneration process (in the first step biomass was degrade by H2-producing bacteria for H2 production, then in the second step the residual from H2-produing phase was used by methanogens for CH4 production) can dramatically increase the energy conversion efficiency from about 20%(hydrogen only production) to about 80%. The maximum specific yield of 342.2 ml-H2/g-glucose and 265.1 ml-CH4/g-glucose was obtained when the initial glucose concentration is 1%, the weight ratio of inoculation to substrate is 2:1 and the pH value was 6. A novel method for enriching H2-prodcing bacteria was adopted, in which Cl- was substituted for SO42-, to increase the hydrogen yield and decrease the yield of H2S. Then the feasibility of cogeneration of H2 and CH4 from starch was investigated. About a 12h lag-phase vanished when improved substrate was used. The maximum specific yield of 271.2 ml-H2/g-TVS and 157.9 ml-CH4/g-TVS was obtained when potatoes were pretreated by a amylase and glucoamylase, and the energy conversion efficiency was 59.6%. Experiments on continuous flow were carried out based on the above researches.Water hyacinth is considered as "One of the world's top ten worst weeds". It is very important to study the feasibility of cogeneration of H2 and CH4 from water hyacinth. The theoretical hydrogen and methane yield was studied. The experimental results indicate that NaOH is a promising reagent for pretreatment of water hyacinth, and 3% is the optimum alkali concentration for the pretreatment of the leaves in the range of 0～5% alkali, compared with other pretreatment methods such as acid, rumen bacteria and ultrasonic. Leaves and stems of water hyacinth pretreated by alkali and cellulase can be used as substrate for H2 production. But the hydrogen yield from the roots of water hyacinth is the lowest, and the enrichment of heavy metals in the roots makes them unsuitable for H2 production. The leaves of water hyacinth has the maximum cogeneration yield of 51.7 ml H2 and 143.4 ml CH4 per gram volatile solid, and the energy efficiency of the cogeneration process is 33.2%.Then a novel combined pretreatment method for water hyacinth was studied, the optimal condition was marinated in alkali for 24 hours, then heated for 10 min at 190℃at a microwave oven, finally 0.05 g-cellulase/g-DM was used to degrade cellulose. After water hyacinth was degrade to glucose by these combined pretreatment method, water hyacinth has the maximum cogeneration yield of 63.9 ml H2 and 172.5 ml CH4 per gram volatile solid, and the energy efficiency of the cogeneration process is 40.0%. When water hyacinth was pretreated by combined pretreatment method, where 0.25 g-cellulase/g-TVS was used to degrade cellulose, it can also be used for methane-only production. And the maximum yield of 237.4 ml-CH4/g-TVS was obtained and the energy efficiency is 49.5%. Finally, large-scale experimental study was carried out in a 50-1 bioreactor before industrial application.