Effect Of Biological Pretreatments On Anaerobic Digestion Of Giant Reed And Corn Stover

Complex structure and the presence of lignin in lignocellulosic biomass usually lead to hydrolysis restrictions during the subsequent anaerobic digestion. Appropriate pretreatment or storage of biomass will potentially increase the biodegradability of lignocellulosic biomass and be helpful to improve the performance of anaerobic digestion for methane production, and consequently promote the improvement and commercialization of anaerobic digestion technology. The performance of ensilage and anaerobic digestion of giant reed harvested at different dates and ensiled at different solid content were evaluated. Effects of and urea addition on ensilage and subsequent anaerobic digestion of giant reed was examined. The effect of fungal pretreatment on physico-chemical properties and subsequent methane production of corn stover was also evaluated.Ensilage and anaerobic digestion of giant reed at different harvest dates on were investigated. The water soluble carbohydrate in giant reed was mainly composed of cellobiose and glucose, which are sugar sources for lactic acid bacteria fermentation during ensilage. When the harvesting time for giant reed was changed from September to December, water soluble carbohydrate significantly increased by 112.9%(p<0.05), and lactic acid accumulation during ensilage increased with a rapid pH drop, which decreased clostridum fermentation and reduced dry mass loss (up to 0.5%). Giant reed harvested in December resulted in the highest stability of ensilage, and thus was used to evaluate the effect of solid content (25%-40%) on ensilage and subsequent anaerobic digestion. Propionic acid accumulation and pH values (up to 4.1) increased with the increase of solid content, indicating enhanced secondary metabolism of lactic acid, but dry mass loss was still less than 1.1%. Compared to non-ensiled giant reed,60-d ensilage resulted in 4.5%-13.7%increase in cumulative methane yields for giant reed harvested from September to December. Higher solids contents (30%-40%) resulted in a 9.6%-14.9% increase in cumulative methane yield via anaerobic digestion for giant reed harvested in December. These suggested that late-harvest could obtain higher WSC contents in giant reed, and then enhance the performance of ensilage and methane production by anaerobic digestion.For early-harvested giant reed (September and October), urea treatment can be used to improve the performance of ensilage. Urea addition (0.8% w/w) directly affected the profile of fermentation products, especially lactic acid, acetic acid and propionic acid during ensilage, and improved the storage performance with reduced dry mass loss and butyric acid generation. Besides, urea addition reduced cellulose degradation (up to 47.5%) while increased lignin degradation (101.3%) during a 90-d ensilage. Ensiled giant reed with urea addition achieved 25.6% and 17.4% higher cumulative methane yields than non-ensiled giant reed which were harvested in September and October, respectively. The production of lactic acid, acetic acid and ethanol, and the improved digestibility of giant reed due to partial degradation of hemicellulose and lignin during ensilage, contributed to the improvement in the maximum methane production rate and cumulative methane yield during the anaerobic digestion process. Ensilage not only increased biodegradability of giant reed, but also reduced start-up time of anaerobic digestion, which is helpful to improve the overall economic efficiency for biogas production.Fungal pretreatment with Phanerochaete chrysosporium improved biodegradability of corn stover silage, with 32.4% hemicellulose degradation and 22.6% lignin degradation, leading to 21.2% increase in the cumulative methane yield during the subsequent anaerobic digestion process. Although fungal pretreatment significantly degraded 61.1% of lignin in dry-yellow corn stover, the methane yield based on initial feedstock decreased, due to the significant loss in cellulose (55.3%). When the corn stover silage was washed prior to fungal pretreatment, degradation of hemicellulose and lignin during fungal pretreatment increased to 48.4% and 39.0%, respectively, resulting in 32.6% higher cumulative methane yield than corn stover silage. Besides, high degradation of lignin (42.9-50.7%) occurred in corn stover with addition of lactic acid or butyric acid during fungal pretreatment, while low lignin degradation (11.7-16.5%) in corn stover was observed with addition of acetic acid or propionic acid. Thus, acetic acid and propionic acid generated from ensilage were considered as major inhibitors to secretion or activity of enzymes during fungal pretreatment with P. chrysosporium. In contrast, lactic acid and butyric acid were less inhibitory to P. chrysosporium.