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

一氧化氮（NO）是烟气中氮氧化物的主要成分。我们发现利用微藻培养系统可以去除烟气中的NO。对于该系统的实际应用，需要提高NO的去除能力，稳定连续的去除NO，以及在室外条件下去除NO。因此，本研究进行了以下调查，以评估该系统的实用性。研究了NO脱除系统的限速因素。在此基础上，可以通过改善栽培条件来提高该体系对NO的去除能力。在光照条件下，NO可以连续脱除。对于室外系统，在明暗循环下驱动系统是很重要的。结果表明，在明暗循环中，暗期弱光照射能成功地实现稳定、连续的NO脱除。通过对细胞内NO去除机制的研究，发现溶解的NO直接进入细胞，氧化为亚硝酸盐和硝酸盐，然后通过氮同化途径消耗。NO对亚硝酸盐和硝酸盐的氧化能力可能由光照条件下的光合作用和黑暗条件下的呼吸作用提供。研究了硫氧化物对烟气中NO的去除效果。结果表明，该体系对低浓度SOx脱硫烟气中NO的脱除效果良好。

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.