| With the depletion of traditional energy sources, the development and use of renewable energy has become an important task for every country. Recently, biological hydrogen and methane production via anaerobic fermentation by using corn straw has attracted much attention. If this process can be extended to an industrial scale, the great practical significance will be achieved to solve the energy problem. Because of pretreatment difficulties during straw saccharification, low utilization rate of substrate, and low volume gas production rate, the production cost of bioenergy from corn straw is relatively high. Therefore, this study investigated effective pretreatment methods for better saccharification of corn straw, and further discussed the relationship between important parameters and biogas production while running the bench-scale and pilot-scale integrated bioreactor (IBR).Exploring the cheap and efficient straw pretreatment method is one of important ways to decrease the cost of anaerobic fermentation. While comparing the effect of acid, alkali,and heat pretreatment method towards wheat straw, the optimum pretreatment method was as follows: liquid ratio 1:15 (g:ml), pretreatment temperature 25? sodium hydroxide concentration 0.2 mol/L, pretreatment time 24 h.Increasing gas production rate of is another effective way to reduce cost of anaerobic fermentation. During the operation of the bench-scale IBR, the highest effective volume gas production rate was 1.2 L/(L d). For the whole operating period, the alkalinity of UASB and CSTR were proportional to the gas production, the Oxidation-Reduction Potential (ORP) of UASB was inversely proportional to the gas production.The computational fluid dynamics technique was used to simulate the sludge flow state in methanogenic phase of the pilot-scale IBR. By regulating the circulation velocity,the bottom dead zone in methanogenic phase of IBR can be prevented to homogenize the sludge particles. The results showed that sludge particle concentration in the basin within 10 to 15 g/L was relatively appropriate. With the increase of concentration of sludge particles, the circulation flow rate should also be enhanced. Under the situation, more sludge particles were deposited, resulted in the increase of unevenness and the floating of sludge particles. When the circulation flow velocity was 7 m/s, there was no sludge particle at export. When the circulation flow velocity was 11 m/s, there were a large number of sludge particle at export.The pilot-scale IBR was operated to verify test data with the bench-scale IBR,and provide operation experience and theoretical guidance for anaerobic fermentation production under industrial scale. By using molasses in start-up period, the UASB and CSTR zones began gas production on the 8th day and 15th day, respectively. the effective volume gas production rate reach 18 L/(L·d) in the CSTR zone, and the hydrogen content was 29% with no methane production. The effective volume gas production rate was 3.0 L/(L-d) in the UASB zone, and the corresponding gas yield reached 132 ml/g-straw with the average methane content of 65%. The appropriate pH in the UASB zone was 6.5 to 7.5, and the ORP was -300 to -350 mV. The appropriate pH in the CSTR zone was 4.0 to 4.5.In order to determine impact factors on the importance of gas production and COD removal, COD concentration, influent pH of the CSTR, ORP of the USAB, and alkalinity of the USAB were chosen as input factors for the simulation of the system. A 3-layers BP neural network was conducted with 4 input layer neurons, 6 middle hidden layer neurons,and 2. output layer neurons. For the following simulation, forecast values and measure values were relatively close with the maximum deviation of 9.7% and the minimum deviation of 0.1%. The separation method of weighting was used to determine relative importance of each factor. For COD removal and gas production, the orders were COD >Alkalinity > ORP > pH, and COD > Alkalinity > pH > ORP, respectively. |
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