BACKGROUNDCost-effective treatment of wastewater remains a challenge for the petroleum industry. In this study, turf soil (R1) was used as a support material in a mesophilic up-flow anaerobic sludge blanket (UASB) reactor for the treatment of petroleum wastewater. RESULTSAt a high organic loading rate (11kg COD/m(3)d), turf soil as a support material reduced COD (91.7%) more efficiently and produced more biogas (1.5m(3)/m(3)d) in comparison with the no support material control (R0) (89.4% and 0.4m(3)/m(3)d). Higher percentages of large granular sludge (0.6mm) were formed in the turf soil-supported UASB reactor (R1), which exhibited better settling, structural resilience and higher biological activity. The rough surface and porous structure of turf soil provided a favorable environment for microbial diversity and habitat. Filamentous bacterial communities putatively promoted anaerobic granular sludge formation and enhanced biodegradation of petroleum organics, particularly alkanes and organic compounds with fewer than 17 carbons. The high content of humic substances promoted the anaerobic degradation of organics, and both humic acid and fulvic acid improved alkaline pH tolerance. CONCLUSIONUse of turf soil enhanced the performance of the UASB system, relative to the control, by shortening the time required to reach stable operation through faster biological community development and improved sludge granulation. (c) 2018 Society of Chemical Industry