Bioremediation of carbofuran contaminated soil and water by Burkholderia sp. PCL3

Abstract

The isolate PCL3, a carbofuran degrader, was previously isolated from carbofuran phytoremediated rhizosphere soil. In this study, the isolate PCL3 was characterized and studied on the potential use to bioremediate carbofuran. From 16s rRNA based identification, PCL3 showed the highest similarity of 96% to Burkholderia cepacia. The effects of carbofuran concentrations (5-200 mg l-1) on biodegradation of carbofuran by the immobilized PCL3 in comparison to free cells were studied in Basal Salt Medium (BSM). The inhibitory effect of carbofuran at the concentration of greater than 100 mg l-1 on the isolate PCL3 in free cells form was observed. The estimated kinetic parameters for free cells of PCL3 from the proposed substrate inhibition model were qmax = 0.451 /d, Ks = 171.96 mg/l, Si = 114.86 mg/l and Sm = 248.76 mg/l. The inhibitory effect was not found when using immobilized PCL3, therefore the Monod equation was used to model the biodegradation kinetic of carbofuran. The qmax values of 0.124 and 0.198 /d and the Ks values of 160.83 and 113.95 for the immobilized PCL3 on corncob and sugarcane bagasse, respectively was obtained. From the kinetic behavior of PCL3, it was confirmed that the immobilization technique could protect the PCL3 cell from substrate inhibition hence enhancing carbofuran degradation efficiency. Free and the immobilized PCL3 on corncob and sugarcane bagasse were further investigated for their abilities to degrade carbofuran in BSM and soil microcosm at the carbofuran concentration of 5 mg l-1 and 5 mg kg-1, respectively. Short half-lives (t1/2) of carbofuran of 3-4 d in BSM were obtained using the isolate PCL3 in both free and immobilized cell forms. Immobilized cells could survive through 30 d of incubation, while the number of free cells decreased continuously after 10 d. Immobilized PCL3 could be reused twice without loss in their abilities to degrade carbofuran in BSM. Free and immobilized cells of PCL3 showed an effective capability to remediate carbofuran residues, both of which indicated by 5-folds decrease in carbofuran half-lives in the augmented soil. The effects of bioremediation techniques, i.e. bioaugmentation by using the immobilized PCL3 on corncob and biostimulation by adding organic amendments together with bioreactors technology in to remove carbofuran from contaminated matrices, soil and aqueous phases, were examined. Soil slurry phase sequencing batch reactors were used to remove carbofuran in contaminated soil at the concentration of 20 mg kg-1 soil. The resultsindicated that bioaugmentation treatment in the soil slurry phase reactor (addition of PCL3) gave the highest percentage of carbofuran removal (96.97%), followed by bioaugmentation together with biostimulation (addition of molasses) treatment (88.23%), suggesting that bioremediation was an effective technology for removing carbofuran from contaminated soil. The sequencing batch reactors (SBRs) augmented with the immobilized PCL3 on corncob were applied to remove carbofuran in aqueous phase (BSM). The effects of hydraulic retention time (HRT), biostimulation, and carbofuran concentrations on the performance of SBRs were investigated. The optimum conditions for SBRs were achieved when it was operated at the HRT of 6 d with the initial carbofuran concentration of 40 mg l-1 by using 0.1 g l-1 of rice brand as a biostimulated amendment. The carbofuran degradation efficiency of SBR at the optimum condition was 100% with the k1 value and t1/2 of 0.044 h-1 and 15.57 h, respectively.