Metabolic pathway of biogas production from the mixture of lignocellulosic waste and animal manure.

This research used wheat, rice, and corn residue as a substrate for biogas production. Due to the high amount of lignin in all three substrates (> 9.9) and to increase the degradability of these substrates, an ultrasonic pretreatment with a power of 150 W at 15 min was used before initiating the enzymatic digestion process. Some physical and chemical properties, including solid and volatile particles and contents of lignin, cellulose and hemicellulose, were measured before and after digesting the substances; in addition, the biogas compounds, including hydrogen methane, hydrogen sulfide and carbon monoxide were measured during digestion. The metabolic pathways of converting glucose as the main constituent of all three waste types into biogas were studied to determine the factors affecting biogas compounds. The results showed that the use of ultrasonic pretreatment in all three wastes increased the breakdown of lignin structures, which decreased the content of these structures in the feedstock compared to the substrate. The amount of solid and volatile particles of the feedstock obtained from the substrate of wheat residue was 35.1% and 95.3%, respectively, which was more than that of the other substrates. The highest amounts of reduction of solid particles (19.6%), volatile particles (18%), cellulose (12.6%), hemicellulose (4.4%) and lignin (3.6%) were related to the feedstock obtained from wheat residue. Analyses of biogas compounds showed the highest biohydrogen production obtained for wheat substrate (ppm 18000), but its biomethane production was lower than the other substrates. The highest amounts of biohydrogen production of all the substrates occurred after seven days, related to the butyrate acidification stage. With increasing digestion time, hydrogen production decreased while the other biogas compounds increased. One of the probable reasons was the consumption of hydrogen produced in the stages of hydrolysis, acidification and acetate formation in the stages of alcoholization and methanation. The highest amount of hydrogen production was related to the butyrate and acetate formation stages. The higher biohydrogen production by wheat residue is most likely due to its high volume of volatile, hydrocarbon and hemicellulose compounds. At the same time, the low production of hydrogen by corn residue was due to driving the reactions towards the production of ethanol and consuming hydrogen. [ABSTRACT FROM AUTHOR]