Biodegradation and toxicity removal of phthalate mixture by Gordonia sp. in a continuous stirred tank bioreactor system

Abstract

This study evaluated degradation of a mixture of six phthalates (dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di-n-octyl phthalate, di-(2-ethylhexyl) phthalate and benzyl butyl phthalate) at different initial concentrations using Gordonia sp in batch shake flasks and in a continuous stirred tank bioreactor. Experiments using simple shake flasks were initially carried out as per the statistically valid 26 1/4 factorial design, which composed of 16 experimental runs with different concentrations of the phthalates. Among the different compounds, dimethyl, diethyl, and dibutyl phthalates, showed more than 99% degradation efficiency even at their high initial concentration. Based on the results of the shake flask study, bioreactor experiments were carried out with 750, 1250 and 1500 mg/L total concentration of the phthalates in mixture. The biodegradation efficiency values of the phthalates using the bioreactor were very high compared with their biodegradation in shake flasks owing to efficient mass transfer, agitation and pH control. Compared to degradation of the compounds at 1500 mg/L total phthalate concentration, the values obtained at 750 mg/L total phthalate concentration were superior (nearly 100% degradation efficiency). The degradation of the high molecular weight phthalates (di-n-octyl phthalate, di-(2-ethylhexyl) phthalate and benzyl butyl phthalate) were better with CSTB as compared to their degradation efficiency values obtained in the batch shake flask study. Very low phytotoxicity of the degraded phthalates further confirmed the potential of Gordonia sp. to treat phthalate contaminated systems.