Studies on practical removal system of NOx from boiler flue gas using microalgae

一氧化氮(NO)是烟气中NOx的主要成分。我们发现，使用微藻培养系统可以从烟气中脱除NO。该系统的实际应用要求提高脱氮能力，稳定连续脱氮，室外条件下脱氮。因此，在本研究中，进行了以下调查以评估该系统的实用性。对脱氮系统中的速率限制因素进行了研究。在此基础上，可以通过改善培养条件来提高该系统对NO的去除能力。在光照条件下，NO可被连续去除。对于户外系统来说，在明暗循环下驱动该系统是非常重要的。研究发现，在明暗周期的暗期照亮弱光，可以实现稳定、连续的NO去除。通过对细胞内NO去除机理的研究表明，溶解的NO直接进入细胞，氧化成亚硝酸盐和硝酸盐，然后通过氮同化途径消耗。光条件下的光合作用和暗条件下的呼吸作用可能提供了NO氧化为亚硝酸盐和硝酸盐的能力。研究了SOx对脱除烟气中NO的影响。结果表明，该系统能有效脱除含低浓度SOx的脱硫烟气中的NO。

Nitric oxide (NO) is a main component of NOx in flue gas. We found that it was possible to remove NO from flue gas using the microalgal culture system. For practical application of this system, improvement of NO removal ability, stable and continuous NO removal, and NO removal under outdoor conditions are required. In this study, therefore, the following investigations were done to evaluate practicability of this system.1. Rate limiting factors in the NO removal system was investigated. Based on that information, the ability of NO removal in this system could be increased by improving cultivation conditions.2. NO could be continuously removed under light condition. For outdoor system, it is important to drive this system under light-dark cycle. It was found that stable and continuous NO removal was successfully achieved by illuminating weak light during dark period in the light-dark cycle.3. By investigation of NO removal mechanism in the cells, it was shown that dissolved NO was directly taken in the cells, oxidized to nitrite and nitrate, and then consumed by the nitrogen assimilation pathway. The oxidation ability of NO to nitrite and nitrate might be supplied by the photosynthesis under light condition and the respiration under dark condition.4. The effect of SOx on NO removal from flue gas was investigated. It was shown that this system was available to remove NO from the desulfurized flue gas containing low concentration of SOx.