Effect of indirect electrochemical pretreatment on the anaerobic digestion of swine manure

The increase in pig population has led to an accumulation of swine manure (SM) in the environment. Improper disposal of this waste can lead to environmental pollution. Anaerobic digestion (AD) is a promising method for utilizing SM, but its industrial application is still limited due to high lignocellulose content and a suboptimal carbon-to-nitrogen ratio. In this study, indirect electrochemical pretreatment (IEP) was used to improve AD of SM. IEP involves treating SM with reactive oxygen species generated by tap water electrolysis. Three different pretreatment modes (acidic-alkaline, acidic, and alkaline-acidic-alkaline) were tested, differing in the time of water flow through the electrochemical unit of the IEP device. Using scanning electron microscopy and UV-V is spectroscopy, it was found that as a result of IEP, the particle size of the SM decreased from 200-500 to 15-50 μm. This led to an increase in biodegradability by 37-38%, compared to untreated SM. Using the alkaline-acid-alkaline pretreatment mode, the highest methane yield of 94,48 ± 1,42 mL CH₄/g VS was obtained, which was 41,28 ± 2,21% higher than in the control group. During AD of pretreated SW, more complex microbial aggregates were observed in the anaerobic microbial community, and the relative abundance of hydrolytic (Bacillus, Ureibacillus, and Geobacillus genera) and syntrophic (Smithella genus and Christensenellaceae R-7 group) microorganisms increased.

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