Biochar amendment of aerobic composting for the effective biodegradation of heavy oil and succession of bacterial community

•Rice husk biochar exhibited hierarchical and three-dimensional structure.•Rice husk biochar accelerated the degradation performance of heavy oil in composting.•The degradation process accorded with the first-order degradation kinetics.•Biochar regulated the microbial abundance at phylum and genus levels in composting.•Nitrogen transformation possessed great impact on microorganism community succession.