Effects of Recycled Biochar Addition on Methane Production Performance in Anaerobic Fermentation of Pig and Cow Manure

Anaerobic fermentation has been recognized as an effective approach to harness livestock manure resources. In the present study, cow dung and pig manure were employed as fermentation substrates. These were subjected to co-fermentation experiments with sodium hydroxide-pretreated corn straw. Additionally, biochar derived from artificial wetland substrate was introduced as a conditioner to investigate the impact of varying addition quantities on the pretreated anaerobic co-fermentation process. Our findings indicate that for the anaerobic co-fermentation of cow dung, an optimal addition of 4% biochar reduced the gas production cycle by 35–45%, although the total methane yield remained relatively unchanged. Conversely, in the anaerobic co-fermentation of pig manure, a 6% biochar addition proved most effective. This adjustment, while not significantly altering the gas production cycle, led to a marked increase in the total methane content, ranging from 18.53% to 150.18%. The PCA analysis results of the cow manure experimental group showed a significant positive correlation between the addition of biochar and ammonia nitrogen. For the pig manure fermentation system, the addition of biochar can increase the final methane production potential, from 47.43 mL/g VS to 122.24 mL/g VS in the P2C experimental group. Biochar mainly regulates the activity of anaerobic bacteria through changes in pH and conductivity, thereby affecting methane production.