Production of biogas by microorganisms with saccharine sorghum straw as substrate with or without alkaline and citric pretreatment

Abstract

This study proposes the use of mixtures of straws with different pretreatments (citric acid or NaOH: urea) and straw in natura, in anaerobic biodigestion. As this straw is a lignocellulosic material with slow degradation by microorganisms, it is necessary to apply pretreatments, increasing biogas production and consumption of volatile solids. The pretreated material can be used to increase the solids content in anaerobic biodigestion reactors operating with large volumes and low volatile solids loads. This study showed a synergistic effect between substrates with different pretreatments and found the best blend for each hydraulic retention time. The ideal mix up to 31 days of hydraulic retention time was from 33.33% to 50.00% of straw pretreated with NaOH: urea and the remainder with straw pretreated with citric acid. After this period, at 46 days, mixtures containing all three components are desirable. At 61 days, factors such as volatile solids reduction and methane content were no longer significant, with a mixture of straw pretreated with citric acid and NaOH: urea at 50% each. These results confirm the importance of straw pre-treatments to reduce the hydraulic retention time, increasing the potential use of cellulosic materials in biodigestion.