چكيده به لاتين
Electrokinetic method is an effective technology for cleaning up heavy metals contaminated soil. The purpose of this research is to design a new bioremediation-electrokinetic (BioEK) remediation process to increase treatment efficiency of chromium (as a model metal) contamination in soil. Therefore, a chromium resistant bacteria consortia was isolated from tannery wastewater and its ability to reduction chromium(VI) in a liquid medium was confirmed. Bio-EK experiments of soil with 20% moisture using medium containing 2.5 (%w/w) glucose and initial concentration of Cr(VI) 500 mg/kg and initial pH of 6.8 were performed in a cubic plastic chamber. In this study, general factorial design was employed to optimize critical parameters responsible for higher Cr(VI) removal/reduction by electrokinetic (EK), bioremediation (Bio) and bioelectrokinetic (BioEK) methods. The factors considered were microbial inoculation (0 and 10%), applied voltage gradient (1 and 2 v/cm) and test time (2, 4 and 6 days). During the process, the variations in electrical gradient, pH, Cr(VI) content output from soil and glucose output from soil were measured. The results showed that in BioEK, EK and Bio, the efficiency of Cr(VI) treatment increased from 96.28, 87.14 and 63.93% to 99.34, 97.91 and 96.83%, respectively, by increasing the time from 2 to 4 days. The effect of applied voltage gradient showed that the amount of residual Cr(III) in the soil at the end of 2 days in BioEK treatment was 191.6 mg/kg and with increasing the voltage gradient from 1 to 2 v/cm reached 267.82 mg/kg. Therefore, it was observed that voltage gradient increasing resulted in the bacteria stimulation and its growth, and subsequently an increase in the bioreduction of Cr(VI) to Cr(III) in the soil. This result showed that the use of carbon source alone in the EK system can increase process efficiency, since carbon sources at low pH from the EK process can reduce chromium(VI). In addition, the use of bacterial consortium in the system themonstrated that the bacteria have a high potential to reduce chromium(VI) in the soil phase. The use of glucose as an electron donor also improved the bioreduction rate of chromium(VI). A statistical analysis of multiple responses based on maximum removal/reduction of chromium(VI) from soil, maximum production of chromium(III), and maximum glucose consumption showed the three variables were significantly effective on the process. Optimum soil remediation conditions were obtained by bioelectrokinetic method in the applied voltage gradient of 1 v/cm and a time of 2 days with more than 96% removal/reduction of chromium (VI).
