Bioreactor performance using biochar and its effect on aerobic granulation.

•The biochars all accelerated granulation and improved reactor performances.•More functional bacteria enriched in the granules with biochars.•Biochars functioned as nucleus for granular formation with EPS as assistant.•Granular sizes are more related to the surface area and pore size of biochar.•Adsorption capacity and functional composition are more correlated to performance.