Hydrogen gas production from agricaltural waste using dark fermentation processes.

Abstract

The global reserves of fossil fuels are depleting due to their increasing consumption. In addition the, environment is facing severe pollution problems due to gaseous emissions (NOx, SOx, CO, CO2, etc.) and waste generated from the production and use of fossil fuels. The objective of this study was to produce hydrogen gas from corn cobs using dark fermentation processes. Unlike fossil fuels hydrogen gas does not cause any CO2, CO, SOx and NOx emissions producing water as its only by-product when it burns reducing greenhouse effects. After corn cobs (samples) were collected in plastic bag reduce the sizes of corn cobs in pestle and dried at 105 °C for 4hr in oven to remove the moisture content and ground to the particle size of 2 mm. After that the sample was exploded by steam explosion pretreatment using 3.5MPa pressure steam in autoclave at 121°C for 15 min. Then the sample was hydrolyzed by adding 2% H2SO4 and filtered under vacuum condition using activated carbon to remove hydrogen production inhibiters such as furfural, hydroxymethaylfurfural (HMF), phenol etc. and stored at 4°C. After that fermentation was carried out by mixing the prepared sample to media ratio (10:1) and maintained its pH at 5.5, 6, 6.5, and 7 by digital pH meter and put it in incubator by adjusting at temperature of 25, 35, 55, and 70°C. Then after 72 hours the produced gas was characterized using gas chromatography. The corn cob used in this study was characterized by 9.2 % moisture content, 9% fixed carbon content, 2.4% ash content and 79.4% relatively high volatile matter content. It was employed dilute acid hydrolysis, because it is easy and productive process. The experiment was designed by Central Composite Design (CCD) with two factor temperature and pH at constant hydraulic retention time (HRT) was maintained at 25, 35, 55, 70°C, and at 5.5, 6, 6.5, and 7 respectively. The maximum yield of 3.18mole of H2 /mole of hexose was observed at a temperature of 69.979°c and pH of 6.964. Significance of the process variables were analyzed using analysis of variance (ANOVA) and second order polynomial function was fitted to the experimental results. Thus, the influence of experimental variables, factors, and interaction effects on the response was investigated. Temperature and pH have a statistically significant effect on the yield with p-value<0.0001.