EFFECT AND MECHANISM OF INORGANIC CARBON ON THE BIODEGRADATION OF DIMETHYL PHTHALATE BY CHLORELLA PYRENOIDOSA

ABSTRACT

The effect and mechanism of inorganic carbon (IC) on the biodegradation of dimethyl phthalate (DMP) by a green microalga Chlorella pyrenoidosa was investigated. It was indicated that DMP could be used as the sole carbon source to support the slow heterotrophic growth of C. pyrenoidosa, but both the growth of C. pyrenoidosa and the biodegradation rate of DMP were obviously increased when initial inorganic carbon concentration (IC) was increased from 0.6 to 23.7 mg/l. Phthalic acid (PA) was found to be an intermediate product of DMP biodegradation and accumulated in the culture solution, which caused a sharp decrease in pH of medium and inhibited both the growth of alga and the biodegradation of DMP. The role of IC for improving the biodegradation of DMP was both to supply a favorite carbon source to support the rapid growth of alga and to mitigate the decrease of pH because of the production of PA. A suggested second-order kinetic equation of organic pollutant biodegradation by microalgae (−dC/dt = K N r) fitted well with the experimental data and the correlation coefficients were all above 0.9. The second-order constant (K) apparently declined with the increase of initial IC because lower ratio between organic carbon from DMP and IC was used to support the growth of alga when initial IC increased.

Keywords:

• Chlorella pyrenoidosa
• Dimethyl phthalate
• Inorganic carbon
• Biodegradation
• Kinetics

ACKNOWLEDGMENTS

The research was supported by Chinese NNSF grant No. 39870133, NNSF grant No. 20073060 and Chinese CAS Grant RCEES-KIP-9901.