Effect of dirhamnolipid on the removal of phenol catalyzed by laccase in aqueous solution.

In this study, the effects of three surfactants, i.e. the anionic biosurfactant dirhamnolipid (diRL), the cationic surfactant hexadecyltrimethyl ammonium bromide (CTAB), and the anionic surfactant sodium dodecyl sulfate (SDS), on the removal of phenol catalyzed by laccase were studied first. CTAB and SDS were detrimental, while diRL improved phenol removal and was selected for detailed research. The biosurfactant increased the activity of laccase and the removal of phenol with the increase of diRL concentrations from 10.6 to 318 μM. DiRL at 318 μM improved the removal when the initial concentrations of phenol were from 50 to 400 mg/l. In particular, the removal of phenol with 318 μM diRL was 4.3-6.4 folds that of the controls within 24 h when the initial concentration of phenol was 400 mg/l. The presence of diRL at 318 μM also caused the complete removal (above 98%) of phenol at concentrations from 50 to 400 mg/l after 24 h. The enhancement of phenol removal was over a wide range of pH and temperatures, and the highest removal efficiency was obtained at pH 6.0 and 50°C. The results suggest that diRL had potential application in the enhancement of phenols removal catalyzed by laccase in water treatment or remediation.