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Biotrickling filters (BTFs) for hydrophobic chlorobenzene (CB) purification are limited by mass transfer and biodegradation.The CB mass transfer rate could be improved by 150 mg/L rhamnolipids.This study evaluated the combined use ofFe3+ and Zn2+ to enhance biodegradation in a BTF over 35 day.The effects of these trace elements were analysed under different inlet concentrations (250,600,900,and 1200 mg/L) and empty bed residence times (EBRTs;60,45,and 32 sec).Batch experiments showed that the promoting effects of Fe3+/Zn2+ on microbial growth and metabolism were highest for 3 mg/L Fe3+ and 2 mg/L Zn2+,followed by 2 mg/L Zn2+,and lowest at 3 mg/L Fe3+.Compared to BTF in the absence of Fe3+ and Zn2+,the average CB elimination capacity and removal efficiency in the presence of Fe3+ and Zn2+ increased from 61.54 to 65.79 g/(m3.hr) and from 80.93％ to 89.37％,respectively,at an EBRT of 60 sec.The average removal efficiency at EBRTs of 60,45,and 32 sec increased by 2.89％,5.63％,and 11.61％,respectively.The chemical composition (proteins (PN),polysaccharides (PS)) and functional groups of the biofilm were analysed at 60,81,and 95 day.Fe3+ and Zn2+ significantly enhanced PN and PS secretion,which may have promoted CB adsorption and biodegradation.High-throughput sequencing revealed the promoting effect of Fe3+ and Zn2+ on bacterial populations.The combination of Fe3+ and Zn2+ with rhamnolipids was an efficient method for improving CB biodegradation in BTFs.