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This is the first study that specifically investigated biosolid-derived biochar for mitigating ammonia stress and methane production during the anaerobic digestion of chicken manure, using both pristine and modified biochar with potassium hydroxide (KOH) solution. Batch mesophilic anaerobic digestion (37 ℃) was carried out over 18 days. Compared to chicken-manure-only controls, a significant increase in methane formation was observed in digesters amended with biochar and KOH-modified biochar, producing 220 L kg-1-VS and 262L kg-1-VS of methane, respectively, compared to 139 L kg-1 VS from control digesters. Moreover, the use of biochar and KOH-modified biochar resulted in a significant reduction of 8 days in the lag phase. Total Ammonia Nitrogen (TAN) concentration was reduced in digesters with biochar and KOH-modified biochar by 25% and 35.5%. respectively. QPCR data revealed that the number of 16S rRNA gene copies was around 50,000 and 41,000 times higher in biochar and KOH-modified biochar digesters, respectively, compared to control digesters on day 18. In addition, adding biochar and alkali-modified biochar to digesters created a mixture of pathways (acetoclastic, hydrogenotrophic and methylation), leading to a robust archaeal community. The results showed that biosolids biochar additives enhance the anaerobic