Effect of the initial pH on the anaerobic digestion process of dairy cattle manure

Abstract

Anaerobic digestion (AD) has recently been studied to obtain products of greater interest than biogas, such as volatile fatty acids (VFAs) and phytoregulators. The effect of the initial pH of cow manure and the fermentation time of the AD on the microbial composition, VFAs, indole-3-acetic acid (IAA) and gibberellic acid (GA3) production was evaluated. The cow manure (7% solids) was adjusted to initial pH values of 5.5, 6.5, 7.5, and 8.5, and the AD products were analyzed every four days until day 20. The initial pH and the fermentation time had an important effect on the production of metabolites. During AD, only the hydrolytic and acidogenic stages were identified, and the bacteria found were from the phyla Firmicutes, Bacteroidetes, Actinobacteria, and Spirochaetes. The most abundant genera produced in the four AD were Caproiciproducens, Clostridium sensu stricto 1, Romboutsia, Paeniclostridium, Turicibacter, Peptostreptococcaceae, Ruminococcaceae and Fonticella. The highest amount of VFAs was obtained at pH 8.5, and the production of the acids was butyric > acetic > propionic. The maximum production of GA3 and IAA was at an initial pH of 6.5 on day 20 and a pH of 5.5 on day 4, respectively. There was a strong correlation (> 0.8) between the most abundant microorganisms and the production of VFAs and GA3. The anaerobic digestion of cow manure is a good alternative for the production of VFAs, GA3 and IAA.

Novel Intelligent System Based on Automated Machine Learning for Multiobjective Prediction and Early Warning Guidance of Biogas Performance in Industrial-Scale Garage Dry Fermentation

“…At pH less than 8, the SHAP values of biogas production were consistently negative, which affected biogas production. In the wet anaerobic digestion of cow manure, the VFA values were 653.3, 609.26, 836.5, and 1150.71 mg/L at pH 5.5, 6.5, 7.5, and 8.5, respectively, and VFA is an intermediate product of AD . VFA accumulation leads to acid inhibition, decreases anaerobic stability, and reduces biogas production .…”

Rumen and Fecal Microbiota Characteristics of Qinchuan Cattle with Divergent Residual Feed Intake

“…Metagenome analysis of microbiota from both HRFI and LRFI groups revealed that, at the phylum level, Bacteroidetes and Firmicutes were the most abundant microbiota in the rumen and feces, consistent with previous studies [ 38 , 39 , 40 ], and the abundance of Bacteroidetes in the rumen was higher in the LRFI group (23.1%) than in the HRFI group (10.1%). Studies have shown that Bacteroidete , Firmicutes and Prevotella can decompose polysaccharides that cannot be digested by the host in the intestinal tract, promoting the digestion and absorption of nutrients which provide energy for the host [ 41 , 42 , 43 ]; these bacteria may have an impact on host feed efficiency by affecting the volatile fatty acid concentration [ 44 ]. The main products of Bacteroidete are phosphobutyryltransferase and butyrate kinase [ 45 ], which promote the fermentation of resistant starch, indigestible oligosaccharides, and their derivatives in the rumen for energy supply, which is conducive to improving feed utilization in ruminants [ 46 ], thereby reducing feed costs.…”

Critical Assessment of Hydrogen and Methane Production from 1G and 2G Sugarcane Processing Wastes Using One-Stage and Two-Stage Anaerobic Digestion

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