Biodegradation of Aromatic Organic Compounds in Alternating Aerobic and Denitrifying Environments

9988086 Grady在美国超过60%的大型生产化学品是芳香有机化合物。因此，它们是废水和环境中的常见污染物。虽然它们的生物降解性取决于它们各自的结构，但一个关键特征，即芳香环，决定了生物降解过程的性质。这是因为细菌在有氧和无氧的情况下使用不同的酶系统来降解芳香族化合物。在有氧条件下，催化它们的酶只有在氧气存在的情况下才能合成和活性。在厌氧条件下，环裂解反应是还原性的。因此，催化它们的酶只有在缺氧的情况下才会合成并具有活性。这就提出了在有氧和厌氧条件下频繁循环的细菌如何降解芳香族化合物的问题。由于与氮排放有关的环境影响，越来越多地采用除氮工艺来处理废水。这种过程采用好氧区和厌氧区，硝酸作为后者的电子受体。在所有这些情况下，人们必须问环境氧化还原状态的变化如何影响芳香族化合物的生物降解。本研究的目的就是要回答这个问题。两种类型的实验将使用在趋化器中生长的细菌混合培养物（没有生物质循环的连续培养物）进行，这将被使用，因为它们允许对细菌生长速度和环境条件进行密切控制。其中一种方法是，将化学调节剂置于不同频率和持续时间的好氧和厌氧交替（以硝酸盐作为电子受体）条件下，以确定所施加循环的性质如何影响培养物去除芳香族化合物的能力。在另一种情况下，少量的氧气将被连续地注入到含有硝酸盐的厌氧化学调节器中。从这项研究中获得的结果将用于制定指导方针，以帮助工程师设计能够将氮和芳香族化合物去除到非常低水平的废水处理系统。它们还将更好地了解细菌在氧化还原状态波动的环境中生长时如何控制对氧敏感的酶，从而帮助科学家更好地预测排放到这种环境中的芳香族化合物的命运。最后，研究结果将帮助工程师确定在含有低溶解氧水平的受污染含水层中添加硝酸盐作为电子受体的效果。＊＊＊

9988086 Grady Over 60% of the large production chemicals in the USA are aromatic organic compounds. Consequently, they are common pollutants in wastewaters and the environment. Although their biodegradabilities depend on their individual structures, one key feature, the aromatic ring, defines the nature of the biodegradation process. This is because bacteria use different enzyme systems to degrade aromatic compounds in the presence and absence of oxygen. Under aerobic conditions, the enzymes catalyzing them are only synthesized and active when oxygen is present. Under anaerobic conditions, the ring cleavage reactions are reductive. Therefore, the enzymes catalyzing them are only synthesized and active when oxygen is absent. This raises questions about how bacterial that are cycled frequently between aerobic and anaerobic conditions degrade aromatic compounds. Because of the environmental impacts associated with the discharge of nitrogen, nitrogen removal processes are being applied with increasing frequency for the treatment of wastewaters. Such processes employ both aerobic and anaerobic zones, with nitrate as the electron acceptor in the latter. In all of these situations one must ask how the variation in redox state of the environment influences the biodegradation of aromatic compounds. The purpose of the proposed research is to answer that question.Two types of experiments will be run with mixed cultures of bacteria grown in chemostats (continuous cultures without biomass recycle), which will be used because they allow close control over both the bacterial growth rate and the environmental conditions. In one, the chemostats will be subjected to alternating aerobic and anaerobic (with nitrate as the electron acceptor) conditions of different frequency and duration to ascertain how the nature of the imposed cycle influences the ability of the culture to remove aromatic compounds. In the other, small quantities of oxygen will be continuously injected into otherwise anaerobic chemostats containing nitrate. The results obtained from this study will be used to derive guidelines to aid engineers faced with the task of designing wastewater treatment systems that are capable of removing both nitrogen and aromatic compounds to very low levels. They will also provide a better understanding of how bacteria control oxygen-sensitive enzymes when grown in environments that have fluctuations in redox state, thereby helping scientists make a better predictions of the fate of aromatic compounds discharged to such environments. Finally, the results will help engineers determine the efficacy of adding nitrate as an electron acceptor to contaminated aquifers containing low levels of dissolved oxygen. ***