Kim Jae-Hong, Von Gunten Urs, Mariñas Benito J
School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0512, USA.
Environ Sci Technol. 2004 Apr 1;38(7):2232-41. doi: 10.1021/es034760w.
A model was developed to simultaneously assess Cryptosporidium parvum oocyst inactivation and bromate formation during ozonation of synthetic solutions in batch and flow-through reactors. The model incorporated 65 elementary chemical reactions involved in the decomposition of ozone and the oxidation of bromine species and their corresponding rate or equilibrium constants reported in the literature. Ozonation experiments were performed with a laboratory-scale batch reactor to evaluate the model with respect to the rate of ozone decomposition and bromate formation. The model was found to provide a good representation of experimental results when the ozone decomposition initiation reaction with hydroxide ion was assumed to produce superoxide radical instead of the alternatively proposed product hydrogen peroxide. The model was further developed to simulate the performance of a flow-through bubble-diffuser reactor with an external recirculation line. Each compartment of the reactor (bubble column and recirculation line) was assumed to behave as a plug flow reactor as supported by tracer test results, and an empirical correlation was used to represent the rate of ozone gas transfer in the bubble column. Model predictions of the performance of the flow-through ozone bubble-diffuser contactor were in good agreement with experimental results obtained for bromate formation and C. parvum oocyst inactivation under all conditions investigated. Additional model simulations revealed that hydrodynamic conditions had a more pronounced effect on C. parvum oocyst inactivation than on bromate formation. In contrast, pH had a strong effect on bromate formation without affecting the inactivation efficiency of C. parvum oocysts for a given level of exposure to ozone. These findings suggested that bromate formation could be minimized while achieving target inactivation levels for C. parvum oocysts by designing ozone reactors with hydrodynamic conditions approaching that of an ideal plug flow reactor and by lowering the pH of the target water.
开发了一个模型，用于同时评估在间歇式和流通式反应器中对合成溶液进行臭氧化处理期间微小隐孢子虫卵囊的失活情况以及溴酸盐的形成。该模型纳入了65个基本化学反应，这些反应涉及臭氧分解以及溴物种的氧化，并且采用了文献中报道的相应速率或平衡常数。使用实验室规模的间歇式反应器进行臭氧化实验，以评估该模型在臭氧分解速率和溴酸盐形成方面的表现。当假定与氢氧根离子发生的臭氧分解引发反应产生超氧自由基而非另一种可能的产物过氧化氢时，发现该模型能够很好地体现实验结果。该模型进一步得到改进，以模拟带有外部循环管线的流通式气泡扩散器反应器的性能。根据示踪剂测试结果，假定反应器的每个隔室（气泡柱和循环管线）都表现为活塞流反应器，并且使用经验关联式来表示气泡柱中臭氧气体的传质速率。在所有研究条件下，对流通式臭氧气泡扩散器接触器性能的模型预测与溴酸盐形成及微小隐孢子虫卵囊失活的实验结果吻合良好。额外的模型模拟结果表明，流体动力学条件对微小隐孢子虫卵囊失活的影响比对溴酸盐形成的影响更为显著。相比之下，对于给定的臭氧暴露水平，pH值对溴酸盐形成有强烈影响，但不影响微小隐孢子虫卵囊的失活效率。这些研究结果表明，通过设计流体动力学条件接近理想活塞流反应器的臭氧反应器，并降低目标水的pH值，可以在实现微小隐孢子虫卵囊目标失活水平的同时，将溴酸盐的形成降至最低。
