## 3 Results and Discussion
### Toxicity Evaluation of Cr(VI) Reduction Products in Batch Treatment  
When 300-mg L\({}^{-1}\) Cr(VI)-containing wastewater was treated by _Ochrobactrum_ sp. CUST210-1 and ChrR in batch, Cr(VI) removal efficiencies achieved 62.5% and 48.5%, respectively. The residual Cr(VI) concentrations were 112.5 mg L\({}^{-1}\) with the CUST210-1 treatment and 154.2 mg L\({}^{-1}\) with the ChrR treatment, respectively. Before treatment, Microtox toxicity (EC\({}_{50}\)) and P. parva (LC\({}_{50}\)) were 18.2-18.5 mg L\({}^{-1}\) and 40.5-40.8 mg L\({}^{-1}\), respectively. After treatment by the CUST210-1 strain, the toxicities of Microtox and P. parva were decreased to 62.4 mg L\({}^{-1}\) and 95.8 mg L\({}^{-1}\). After treatment by ChrR, the toxicities of Microtox and P. parva were decreased to 86.2 mg L\({}^{-1}\) and 123.5 mg L\({}^{-1}\), respectively. For _Ochrobactrum_ sp. CUST210-1 and ChrR, respectively, 57.8-70.3% and 67.0-78.9% detoxification efficiencies were achieved. Thus, the ChrR had higher detoxification efficiency than the bacterial cells. Notably, although the removal efficiency of the CUST210-1 strain was higher than that of ChrR protein, the reverse was true for detoxification efficiency. This may be attributed to the Cr(VI) product from the ChrR treatment being relatively simpler than that of the bacteria [5]. It also indicates the advantage and potential of the Cr(VI) treatment by ChrR. Effects of Operating Parameters on Continuous Cr(VI) Removal by Immobilized Ochrobactrum sp. CUST210-1 Biosystem  
Figure 3A presents the effect of LRT on the continuous treatment of synthetic Cr(VI)-containing wastewater by the immobilized _Ochrobactrum_ sp. CUST210-1 biosystem. The results indicate that the removal efficiency for Cr(VI) gradually increased, but the removal capacity for Cr(VI) gradually decreased as the LRT increased. When the LRT was 4 h, the removal efficiency achieved 100%, and the removal capacity achieved an acceptable level of \(1.71\pm 0.2\times 10^{-9}\) mg-Cr(VI) (cfu-h)\({}^{-1}\). Thus, the operating LRT of the experiment was set at 4 h. Temperature and pH play a key role in the growth of bacterial strains; hence, their effects on the removal characteristics for Cr(VI) were evaluated. Figure 3B represents the effect of pH on the continuous treatment of synthetic Cr(VI)-containing wastewater. A pH of 7-8.5 had a nonsignificant effect (\(p>0.05\)) on the removal efficiency for Cr(VI), and the removal efficiency achieved \(>\)99.2% \(\pm\) 0.1%. Moreover, a pH of 7-9 had a nonsignificant effect (\(p>0.05\)) on the removal capacity for Cr(VI), and the removal capacity was maintained in the range of \(1.60\pm 0.05\) to \(1.67\pm 0.01\times 10^{-9}\) mg-Cr(VI) (cfu-h)\({}^{-1}\). To consider the characteristics of  
Figure 2: Crystal structure of ChrR in _Ochrobactrum_ sp. CUST210-1. Cr(VI)-containing wastewater and the operational performance of the biosystem, the pH value of the experiment was controlled at 7.0. An optimal Cr(VI) reduction at pH 7.0 was determined for Bacillus sp., P. aeruginosa, and S. maltophilia [14; 36; 41]. The decrease in Cr(VI) reduction efficiency at pH 9.0 was mainly attributed to the possibility that deviation from appropriate pH values may affect the degree of ionization of ChrR [36]. These results indicate the _Ochroductrum_ sp. CUST210-1 biosystem had good adaptability to pH changes. Figure 3C displays the effect of the operating temperature on the continuous treatment of synthetic Cr(VI)-containing wastewater. An operating temperature between 30 \({}^{\circ}\)C and 40 \({}^{\circ}\)C had a nonsignificant effect (\(p>\) 0.05) on the removal efficiency, and an efficiency \(>\)99.5% was achieved. By contrast, Cr(VI) reduction by Serratia rubidaea and C. funkei was greatly influenced by temperature in a similar temperature range [35; 42]. These results indicate the _Ochroductrum_ sp. CUST210-1 had a high adaptability to temperature changes compared with other bacterial strains.