Research On Factors By Anaerobic Fermentation Of Straw

As an agricultural country, there are a lot of wastes in the process of agricultural production in China. The output of straw stalk is more than700million tons per year, but the utilization ratio is very low. A large number of straw will be burn in the field, which causes the serious air pollution, and waste precious renewable resources. At the same time, with the intensification of world and the acceleration of urbanization process, dependence on oil, coal and other fuels, extensive use of pesticides and fertilizers and the landfill of solid waste produced from arbitrary city life lead to a variety of chemical speciation of heavy metal pollutants released into the environment constantly. Therefore, this paper combined straw anaerobic fermentation and heavy metal ions, which not only can avoid the environmental pollution brought by the straw burning and heavy metal ions, also can produce renewable energy, biogas. The experimental results of this paper are as follows.Firstly, we pretreated the raw material, and did the experiments to contrast four aspects, such as acid and alkali, different alkali charge, pretreatment time and pretreatment with different methods. Then we texted the results by FTIR, SEM, COD, TG and gas production, so that we got the optimal pretreatment method:15g straw and100ml of6%NaOH solution heat for1h.Secondly, we constructed the anaerobic fermentation system and studied the effect of raw material type, temperature, C/N and inoculum on anaerobic fermentation gas production. Then we got the optimal anaerobic fermentation conditions:the straw after pretreatment adjusted to pH=6-7, the carbamide making the C/N of system25:1,50ml biogas slurry, and36℃for fermentation temperature.Lastly, we put heavy metal ions Cd2+, Hg2+in the optimition anaerobic fermentation system to study how the heavy metal ions influence the gas of anaerobic fermentation. We found microorganisms in the process of fermentation were very sensitive to the environment. When tht heavy metal concentration in the biogas slurry was low, anaerobic fermentation could produce gas steadily, but when the concentration was high, the activity of microorganisms was restrained and even poisoned. The toxicity of digestive process mainly depended on the existence form of heavy metals. The precipitation state of heavy metal had no effect on biological systems, and dissolved heavy metal ions in the anaerobic fermentation process had the effect of the inhibition. System of dissolved metal ions was not only related to the amount of the original, but also related the system itself which can make the metal ion precipitation formation (i.e., buffering capacity). Anaerobic fermentation system with heavy metals, still could produce gas, because there were carbonate and sulfides in the anaerobic system which could precipitate heavy metals, which could mask the toxicity. But this ability was limited. When the concentration of heavy metal reached a certain value in the system, a large amount of soluble heavy metal ions in the biogas slurry had bad effects on the anaerobic microbes, which made the microorganisms poisoned, so that the reaction was restrained. And the concentrations of heavy metal allowed by the fermentation system were Cd2+:5mg/L, Hg2+:2.5mg/L, respectively.