Hsueh H T, Chu H, Yu S T
Department of Environmental Engineering, National Cheng Kung University, 1 University Road, Tainan 701, Taiwan.
Chemosphere. 2007 Jan;66(5):878-86. doi: 10.1016/j.chemosphere.2006.06.022. Epub 2006 Jul 24.
Carbon dioxide mass transfer is a key factor in cultivating micro-algae except for the light limitation of photosynthesis. It is a novel idea to enhance mass transfer with the cyclic procedure of absorbing CO(2) with a high performance alkaline abosorber such as a packed tower and regenerating the alkaline solution with algal photosynthesis. Hence, the algae with high affinity for alkaline condition must be purified. In this study, a hot spring alga (HSA) was purified from an alkaline hot spring (pH 9.3, 62 degrees C) in Taiwan and grows well over pH 11.5 and 50 degrees C. For performance of HSA, CO(2) removal efficiencies in the packed tower increase about 5-fold in a suitable growth condition compared to that without adding any potassium hydroxide. But ammonia solution was not a good choice for this system with regard to carbon dioxide removal efficiency because of its toxicity on HSA. In addition, HSA also exhibits a high growth rate under the controlled pHs from 7 to 11. Besides, a well mass balance of carbon and nitrogen made sure that less other byproducts formed in the procedure of carboxylation. For analysis of some metals in HSA, such as Mg, Mn, Fe, Zn, related to the photosynthesis increased by a rising cultivated pH and revealed that those metals might be accumulated under alkaline conditions but the growth rate was still limited by the ratio of bicarbonate (useful carbon source) and carbonate. Meanwhile, Nannochlopsis oculta (NAO) was also tested under different additional carbon sources. The results revealed that solutions of sodium/potassium carbonate are better carbon sources than ammonia carbonate/bicarbonate for the growth of NAO. However, pH 9.6 of growth limitation based on sodium was lower than one of HSA. The integrated system is, therefore, more feasible to treat CO(2) in the flue gases using the algae with higher alkaline affinity such as HSA in small volume bioreactors.
除了光合作用受到光照限制外，二氧化碳传质是微藻培养中的一个关键因素。利用高效碱性吸收器（如填料塔）吸收二氧化碳并通过藻类光合作用再生碱性溶液的循环过程来强化传质，这是一个新颖的想法。因此，必须筛选出对碱性条件具有高亲和力的藻类。在本研究中，从台湾的一个碱性温泉（pH 9.3，62℃）中纯化出一种温泉藻（HSA），该藻在pH超过11.5和50℃的条件下生长良好。就HSA的性能而言，在合适的生长条件下，填料塔中的二氧化碳去除效率比不添加任何氢氧化钾时提高了约5倍。但由于氨溶液对HSA有毒性，因此对于该系统的二氧化碳去除效率而言，它不是一个好的选择。此外，HSA在pH值控制在7至11的条件下也表现出较高的生长速率。此外，良好的碳氮质量平衡确保了羧化过程中产生的其他副产物较少。对于分析HSA中一些与光合作用相关的金属，如镁、锰、铁、锌，发现随着培养pH值的升高而增加，这表明这些金属可能在碱性条件下积累，但生长速率仍受碳酸氢盐（有用碳源）与碳酸盐比例的限制。同时，还对隐甲藻（NAO）在不同附加碳源下进行了测试。结果表明，对于NAO的生长，碳酸钠/钾溶液是比碳酸铵/碳酸氢盐更好的碳源。然而，基于钠的生长限制pH值9.6低于HSA的生长限制pH值。因此，在小体积生物反应器中使用具有较高碱性亲和力的藻类（如HSA）来处理烟道气中的二氧化碳，该集成系统更可行。
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