Enhanced biodegradation of n-hexane from the air stream using rhamnolipid in a biofilter packed with a mixture of compost, scoria, sugar beet pulp and poplar tree skin

Biofiltration of n-hexane vapors with and without using rhamnolipid biosurfactant was investigated on a laboratory scale biofilter packed with compost, scoria, sugar beet pulp, and poplar tree skin at empty bed residence times (EBRT) of 30, 60 and 120s for a period of 131 days. Acclimation of microorganism in the biofilter was achieved in 31 days with an average n-hexane concentration of 0.269 gm(-3) and EBRTs of 120s. The results demonstrated that average removal efficiencies (RE) for the corresponding EBRT with n-hexane loading rates (IL) of 6.7-137 gm(-3)h(-1) were 18.7 +/- 1.67%, 28.9 +/- 4.06% and 46.8 +/- 8.2% without biosurfactant. While, the average REs in presence of the biosurfactant were 23.98 +/- 4.08%, 42.4 +/- 9.7% and 85.13 +/- 10.44% at EBRTs of 30, 60 and 120s, respectively. About 53% of n-hexane removal was related to the segment 1 of the biofilter, where the bacterial and fungi population of its biofilm was 2 x 10(15) and 1.3 x 10(9) CFU g(-1) (dry weight), respectively, which was significantly more than the other segments. For all the tested inlet concentrations, the RE was significantly increased by increasing EBRT and decreasing IL of n-hexane. The results of this study confirm the efficiency enhancement of rhamnolipid in biofiltration of hydrophobic compounds such as n-hexane from air streams.