Development of high performance bioreactor system for aerobic microbial degradation of trichloroethylene

为了开发一种高效的利用琼脂糖凝胶包埋的恶臭假单胞菌KF 715-D 6重组细胞降解三氯乙烯（TCE）的生物反应器系统，我们优化了各种操作参数，以保持细胞在较长时间内的活性和稳定性。所得结果如下所述：降解温度设定为15 ℃，因为在该温度下获得的稳定性最高，尽管在30 ℃下出现最高活性。最佳的再活化条件是在含有0.2 mM葡萄糖和5 mM甲酸盐的基础盐培养基（BSM）中，在4 ℃和pH 6.5下孵育6 h。在此条件下进行细胞再活化，与30 ℃降解相比，剩余活性由30%提高到60%，用优化的BSM代替水作为降解介质，活性和稳定性分别提高了50%和10%。此外，澄清了细胞降解TCE的能力受到培养条件如振荡速度和培养时间（细胞收获的生长阶段）的显著影响。在指数生长期收获的细胞表现出活细胞密度、初始活性、剩余活性和降解能力的最高性能。然而，在早期稳定期收获细胞以获得大量的生物质。在此基础上，提出了一种由疏水中空纤维膜组件和琼脂糖凝胶包埋细胞悬浮于BSM中的TCE降解容器组成的生物反应器系统。

In order to develop a highly efficient bioreactor system for the biodegradation of trichloroethylene (TCE) using agarose gel-entrapped recombinant cells of Pseudomonas putida KF715-D6, we optimized various operating variables for maintaining the activity and stability of the cells over a longer time of degradation. The results derived have been described below :The degradation temperature was set at 15 ℃ because the highest stability was obtained at this temperature, although the highest activity was appeared at 30 ℃. The optimum reactivating condition was to incubate the cells for 6 h in a basal salt medium (BSM) involving 0.2 mM glucose and 5 mM formate at 4 ℃ and pH 6.5. By reactivating the cells under such a condition, the remaining activity was doubled from 30 % to 60 %, compared with the case of degradation at 30 ℃ without reactivation.By using the optimized BSM in place of water as the degradation medium, the activity and the stability were increased by 50 % and 10 %, respectively. In addition, it was clarified that the capability of the cells for the TCE degradation was significantly influenced by the cultivation conditions such as shaking speed and cultivation time (the growth phase of cell harvesting). The cells harvested during the exponential growth phase exhibited the highest performance for the viable cell density, initial activity, remaining activity and degradation capacity. However, the cells were harvested at an early stationary phase to obtain a large amount of the biomass. By using BSM as the degradation medium and by reactivating the cells in BSM for 18 h, more than 90 % of the remaining activity was maintained.Based upon the experimental results described above, a bioreactor system composed of a hydrophobic hollow fiber membrane module for the separation of TCE and a TCE degradation vessel in which the agarose gel-entrapped cells were suspended in BSM, was proposed.