| Corn stover is an abundant biomass and inevitable co-product of corn grain product in China. With the characteristics of distributed dispersion, lower bulk density, seasonal and higher transportation costs, a large amount of corn stover has not been effectively used and abandoned as solid waste and even burnt in the open field directly, which is causing severe environmental problems. Anaerobic digestion has proven to be an environment-friendly technology to convert corn stover to clean biogas to achieve its resource utilization. Theoretical methane yield of corn stover was calculated to be 431.2 mL·gvs-1 according to the elements analysis results. Corn stover with complex lignocellulosic structure, it is necessary to do some pretreatment work to break the connection between lignin and cellulose components in order to increase the hydrolysis speed in the process of anaerobic fermentation and improve the biogas conversion efficiency. In this study, the effects of potassium hydroxide and calcium hydroxide pretreatment on the performance of anaerobic digestion and influence on the corn stover structure were studied.Firstly, select KOH and Ca(OH)2 as pretreatment reagent, the corn stover was pretreated with different concentrations (0.5%,1.0%,1.5%,2.0%,2.5%,3% w/v) of KOH and Ca(OH)2 respectively at room temperature (20?) to investigate the performance of anaerobic digestion. In addition, by scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis and other means to discuss the influence mechanism of different pretreatment conditions on the structure of corn stover. The results showed that KOH pretreatment effect is obviously better than that of Ca(OH)2 pretreatment under the same concentration of alkali at room temperature, the best KOH pretreatment concentration was 2.5%, which could achieve cumulative methane production of 295.0 mL·gvs-1, 95.6% improvement compared with that of untreated one. KOH and Ca(OH)2 pretreatment can effectively remove lignin and hemicellulose content, and the higher alkali concentration, the better the removal efficiency is.In order to save pretreatment cost, the combined alkaline pretreatment of KOH and Ca(OH)2 were carried out at room temperature to improve the biogasification of corn stover for high-efficiency anaerobic digestion. The results indicated that combined alkaline pretreatment could reduce the KOH dose and achieve similar pretreatment effects. The combination of 0.5% KOH and 2.0% Ca(OH)2 was comparable to the effect of 2.0% KOH pretreatment, achieving a cumulative methane yield of 271.4 mL·gvs-1, which was 77.0% higher than untreated corn stover.In addition, the impact of thermo-alkaline pretreatment on the anaerobic digestion of corn stover was studied. The corn stover was pretreated with different concentrations (0.5%,1.5%,2.0%,2.5% w/v) of KOH and Ca(OH)2 respectively, and different ratio of combined KOH and Ca(OH)2 pretreatment at 55?.The results showed that the single thermo-alkali pretreatment could significantly improve the anaerobic digestion of corn stover.2.0% KOH reached the maximum methane value of 290.8 mL·gvs-1,which increased 86.6% compared with untreated one. The combination of 0.5% KOH and 2.0% Ca(OH)2 achieved a cumulative methane yield of 247.3 mL·gvs-1, which was comparable with the effects of 1.5% KOH and 1.5% Ca(OH)2 pretreatment. The cumulative methane yield of 1.5% Ca(OH)2 at 55? was 242.2 mL·gvs-1, which showed 19.7% improvement compared with the same alkali concentration at 20?. However, the effect of the thermo-combined alkali pretreatment was inferior to that of the combined alkali pretreatment at normal temperature. Therefore, from the cost savings point of view,1.5% Ca(OH)2 pretreatment at 55? was the most appropriate condition. |
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