2.5. Statistical analysis
Multivariate analysis was performed using two algorithms: PCA and 2-D HCA heat map. The PCA, based on the correlation matrix, was performed using XLStat-Pro 2015 software. The 2-D HCA heat map was carried out with the ArrayTrack, and the Ward's minimum-variance method was used for runs and hydrocarbons clustering. A probability level of p=0.05 was considered as significant difference.
The data obtained from the RSM on the hydrocarbon removal were subjected to the analysis of variance (ANOVA) and the results were fitted to the following second-order polynomial equation (Vieira et al., 2009; Gomez and Sartaj, 2014): where Y is the predicted response (hydrocarbons removal), XiXj are the independent variables, β0 is …show more content…
The highest bioremoval occurred for toluene/benzene, followed by ethylbenzene and m,p-xylene, and the lowest for o-xylene. For toluene, the lowest bioremoval (76.7%) occurred at run/treatment 13, while the highest bioremoval (98.3%) at run 14 (Table 2). The lowest and highest bioremoval of other hydrocarbons also occurred at runs 13 and 14, respectively. The originally toluene-adapted and toluene-removing bacterium could also remove benzene very well, but not xylenes, even after almost several years of adaptation using BTEX mixture as a sole carbon and energy source. The microbial utilization of hydrocarbons is known dependent on the contaminants chemical structures, and an extensive methylation (as in xylenes) can inhibit the initial oxidation of contaminants (Atlas, 1981). However, the bioremoval of BTEX under the aerobic condition in current study was still much higher compared to the previous study under the anaerobic condition (Dou et al., 2008) where very little biodegradation was observed for all six single BTEX substrates (at 25-150 mg kg-1 each) after 10-day incubation using the augmented microorganisms and all BTEX compounds could be anaerobically biodegraded to the non-detectable levels within 70 days when the initial concentrations were below 100 mg kg-1 in soil. The BTEX biodegradation is generally considered faster under the aerobic conditions than the anaerobic (Wolicka et al., 2009). The bioremoval of BTEX (600 mg kg-1) after 6-day incubation in current study was also higher compared to the biodegradation of BTEX (400 mg kg-1 soil dry wt) after 18-day incubation (Margesin et al., 2003). At 600 mg kg-1 BTEX, the highest bioremoval occurred for ethylbenzene (70%), followed by toluene (49%) and benzene (27%), but almost negligible for
Multivariate analysis was performed using two algorithms: PCA and 2-D HCA heat map. The PCA, based on the correlation matrix, was performed using XLStat-Pro 2015 software. The 2-D HCA heat map was carried out with the ArrayTrack, and the Ward's minimum-variance method was used for runs and hydrocarbons clustering. A probability level of p=0.05 was considered as significant difference.
The data obtained from the RSM on the hydrocarbon removal were subjected to the analysis of variance (ANOVA) and the results were fitted to the following second-order polynomial equation (Vieira et al., 2009; Gomez and Sartaj, 2014): where Y is the predicted response (hydrocarbons removal), XiXj are the independent variables, β0 is …show more content…
The highest bioremoval occurred for toluene/benzene, followed by ethylbenzene and m,p-xylene, and the lowest for o-xylene. For toluene, the lowest bioremoval (76.7%) occurred at run/treatment 13, while the highest bioremoval (98.3%) at run 14 (Table 2). The lowest and highest bioremoval of other hydrocarbons also occurred at runs 13 and 14, respectively. The originally toluene-adapted and toluene-removing bacterium could also remove benzene very well, but not xylenes, even after almost several years of adaptation using BTEX mixture as a sole carbon and energy source. The microbial utilization of hydrocarbons is known dependent on the contaminants chemical structures, and an extensive methylation (as in xylenes) can inhibit the initial oxidation of contaminants (Atlas, 1981). However, the bioremoval of BTEX under the aerobic condition in current study was still much higher compared to the previous study under the anaerobic condition (Dou et al., 2008) where very little biodegradation was observed for all six single BTEX substrates (at 25-150 mg kg-1 each) after 10-day incubation using the augmented microorganisms and all BTEX compounds could be anaerobically biodegraded to the non-detectable levels within 70 days when the initial concentrations were below 100 mg kg-1 in soil. The BTEX biodegradation is generally considered faster under the aerobic conditions than the anaerobic (Wolicka et al., 2009). The bioremoval of BTEX (600 mg kg-1) after 6-day incubation in current study was also higher compared to the biodegradation of BTEX (400 mg kg-1 soil dry wt) after 18-day incubation (Margesin et al., 2003). At 600 mg kg-1 BTEX, the highest bioremoval occurred for ethylbenzene (70%), followed by toluene (49%) and benzene (27%), but almost negligible for