Impact of solids on biphasic biodegradation of phenanthrene in the presence of hydroxypropyl-β-cyclodextrin (HPCD)

The consequence of polycyclic aromatic hydrocarbons (PAHs) in the environment is of great concern. The hydrophobic properties of PAHs significantly impact phase distribution causing limited bioavailability. Enhanced biodegradation has been extensively carried out by surfactants and the redeployment effect was recognized. However, the quantitative relationship concerning the impact of solids was rarely reported. A batch of biphasic tests were carried out by introducing Mycobacterium vanbaalenii PYR-1 and hydroxypropyl-β-cyclodextrin (HPCD) into a mixture of phenanthrene solution and various glass beads (GB37-63, GB105-125, and GB350-500). The comparative results demonstrated that HPCD had little effect on microbial growth and was not degradable by bacterium. A model was proposed to describe the biodegradation process. The regression results indicated that the partition coefficient k_d (1.234, 0.726 and 0.448 L·g^-1) and the degradation rate k (0 mmol·L^-1: 0.055, 0.094, and 0.112; 20 mmol·L^-1: 0.126, 0.141, and 0.156; 40 mmol·L^-1: 0.141, 0.156 and 0.184 d^-1) were positively and negatively correlated with the calculated total surface area (TSA) of solids, respectively. Degradation enhanced in the presence of HPCD, and the enhancing factor f was calculated (20 mmol·L^-1: 15.16, 40.01, and 145.5; 40 mmol·L^-1: 13.29, 37.97, and 138.4), indicating that the impact of solids was significant for the enhancement of biodegradation.