A batch study on the bio-fixation of carbon dioxide in the absorbed solution from a chemical wet scrubber by hot spring and marine algae.

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.

Carbon bio-fixation by photosynthesis of Thermosynechococcus sp. CL-1 and Nannochloropsis oculta.

There is a great potential to assimilate CO(2) and produce bio-energy from cellular component by utilizing carbon fixation of photosynthetic microorganisms. Two different types of photosynthetic microorganisms were used in the present study. The strain Thermosynechococcus sp. CL-1 (TCL-1) was previously isolated from a hot spring while Nannochloropsis sp.Oculta (NAO) from sea water. Two types of inorganic carbon were used (gaseous CO(2) and dissolved inorganic carbon, DIC) with nitrate as N source under different temperature conditions. The Monod model was used to relate its growth rate and DIC concentration. Additionally, lipid and carbohydrate of cell component, which can be used as bio-energy precursors, as function of CO(2) and DIC concentrations is quantified. The growth rate of TCL-1 decreased as CO(2) concentrations increased from 10% to 40% due to low pH inhibition with the maximum value 2.7 d(-1) at 10% CO(2). As for NAO, the maximum growth rate of about 1.6 d(-1) was obtained at 5% and 8% CO(2) (pH between 5.5 and 7 at 30 degrees C). Regarding the cultivation of TCL-1 under various DIC concentrations, the maximum growth rate of TCL-1 was 3.5 d(-1) at the initial DIC 94.3 mM, pH 9.5 and 50 degrees C. The carbohydrate content of TCL-1 increased from 2.1% to 33% as DIC concentration increased from 4.7 to 94.3 mM. However, the 33% carbohydrate content at 94.3 mM DIC was much less than 61% at 10% CO(2). That may be due to the fact that the cultivation at 94.3 mM DIC can not supply adequate amounts of DIC to produce carbohydrate under N-limiting conditions. Conversely, enough amounts of DIC supplied from washing flue gas for cultivating TCL-1 would provide a higher performance of carbon bio-fixation and carbohydrate production.

Spray scrubbing of the nitrogen oxides into NaClO2 solution under acidic conditions.

The operating conditions of this study were closed to the typical operating conditions of flue gas desulfurization system in the coal-fired power plant. The objective of this study was to investigate the absorption performance of lean NO in an aqueous solution of acidic sodium chlorite using a bench-scale spraying column. The NO conversion and NOx removal efficiency were increasing with the increasing NO concentration, retention time, sodium chlorite concentration, operating temperature, and decreasing initial pH of solution. As the sodium chlorite concentration were higher than 0.4 M, the NO conversion and NOx removal efficiency were 100% and 80%, respectively. The NO conversion and NOx removal efficiency under initial pH 4-7 were higher than that of initial pH > 7. It meant that this process might be suitable to combining with traditional wet flue gas desulfurization system. As the NO2/NOx ratio in the effluent gas was closed to 0.5, it might be suitable to be absorbed in the second scrubbing column operated under alkaline condition.