Reduction of CO2 by a high-density culture of Chlorella sp. in a semicontinuous photobioreactor

The microalga incorporated photobioreactor is a highly efficient biological system for converting CO2 into biomass. Using microalgal photobioreactor as CO2 mitigation system is a practical approach for elimination of waste gas from the CO2 emission. In this study, the marine microalga Chlorella sp. was cultured in a photobioreactor to assess biomass, lipid productivity and CO2 reduction. We also determined the effects of cell density and CO2 concentration on the growth of Chlorella sp. During an 8-day interval cultures in the semicontinuous cultivation, the specific growth rate and biomass of Chlorella sp. cultures in the conditions aerated 2-15% CO2 were 0.58-0.66 d(-1) and 0.76-0.87 gL(-1), respectively. At CO2 concentrations of 2%, 5%, 10% and 15%, the rate of CO2 reduction was 0.261, 0.316, 0.466 and 0.573 gh(-1), and efficiency of CO2 removal was 58%, 27%, 20% and 16%, respectively. The efficiency of CO2 removal was similar in the single photobioreactor and in the six-parallel photobioreactor. However, CO2 reduction, production of biomass, and production of lipid were six times greater in the six-parallel photobioreactor than those in the single photobioreactor. In conclusion, inhibition of microalgal growth cultured in the system with high CO2 (10-15%) aeration could be overcome via a high-density culture of microalgal inoculum that was adapted to 2% CO2. Moreover, biological reduction of CO2 in the established system could be parallely increased using the photobioreactor consisting of multiple units.     

产油嗜碱绿球藻MC-1的烟气适应性

为了降低微藻产油成本和减少温室气体的排放,利用煤炭烟气培养一株具有pH快速漂移和高碱适应特性的产油微藻Chlorococcum alkaliphilus MC-1.首先于15L光生物反应器中分三组(空白组、CO2组和烟气组)进行小体积培养实验,然后在24 m2开放式跑道池中进行放大培养,研究了微藻MC-1对烟气培养的适应性.结果表明,在光生物反应器培养实验中,烟气组的最高生物量浓度、生长速率、藻体总脂含量和CO2固定速率分别为:(1.02±0.07) g/L、(0.12±0.02) g/(L·d)、(37.84±0.58)％和(0.20±0.02) g/(L·d),比CO2组分别提高了36％、33.33％、15.34％和33.33％.在开放式跑道池培养实验中,烟气与纯CO2的培养效果相似,烟气培养下的最高生物量浓度、生长速率、藻体总脂含量和CO2固定速率分别为:147.40 g/m2、14.73 g/(m2·d)、35.72％和24.01 g/(m2·d);烟气培养产出的藻粉中有毒重金属Pb、As、Cd和Cr的含量均低于国家限量标准.实验同时测定了烟气培养下藻液对烟气中CO2、NO和SO2的吸收效果,结果显示,在光生物反应器和开放式跑道池培养中此三种气体的平均吸收率均高于以往研究结果.上述结果说明,该藻能适应烟气培养条件,耦合微藻MC-1产油与烟气减排的室外放大培养是可行的.     

Effects of SO2 and NO on growth of Chlorella sp. KR-1

Effects of the toxic compounds in flue gas, SOx and NOx, on growth of Chlorella sp. KR-1 have been determined. Although growth of KR-1 was suppressed by the toxic compounds, KR-1 exhibited excellent tolerances to SOx compared to other algal strains. When Chlorella KR-1 was cultured with the model gas containing 60 ppm SO2, the linear growth rate was 1.24 g/l day which is about 25% lower than that of the control culture aerated with the gas mixture containing no toxic compounds, SO2 and NO. KR-1 could grow even with the model gas containing 100 ppm SO2 and the linear growth rate of KR-1 in the culture was 0.78 g/l day. The period for lag phase was increased with increasing of SO2 concentration that also resulted in the decrease of the linear growth rate and the maximum cell concentration. Direct CO2 fixation by Chlorella KR-1 has been successfully done using actual flue gases from a liquified natural gas (LNG)- or diesel-fueled boiler. These results indicated that Chlorella KR-1 may be applied for direct CO2 fixation from actual flue gas.     

Bioflocculation of microalgae and bacteria combined with flue gas to improve sewage treatment

Although microalgae are promising for a cradle-to-cradle design approach of sewage treatment, their application is hampered by high harvesting costs and low C:N ratios of sewage. Therefore, the potential of microalgal bacterial flocs (MaB-flocs) was investigated for the secondary treatment of sewage supplemented with different flue gas flow rates (FGFRs) from a coal power plant. Effluent (N, P, turbidity and pH) and off gas discharge levels (NO(x), SO(x)) met the European discharge limits with a hydraulic retention time of only 0.67 days and an FGFR of 0.6Lh(-1) (0.0025 vvm). This FGFR provided sufficient carbon and resulted in removal efficiencies of 48 ± 7% CO(2), 87 ± 5% NO(x) and 99 ± 1% SO(2). MaB-flocs settled fast reaching up to a density of 19 g VSSL(-1). High biomass productivities (0.18 gL(-1)day(-1)) were obtained under a low light intensity. This successful reactor performance indicates the large potential for the industrial application of MaB-flocs for flue gas sparged sewage treatment.     

The air‐lift photobioreactors with flow patterning for high‐density cultures of microalgae and carbon dioxide removal

A photobioreactor containing microalgae is a highly efficient system for converting carbon dioxide (CO₂) into biomass. Using a microalgal photobioreactor as a CO₂ mitigation system is a practical approach to the problem of CO₂ emission from waste gas. In this study, a marine microalga, Chlorella sp. NCTU‐2, was applied to assess biomass production and CO₂ removal. Three types of photobioreactors were designed and used: (i) without inner column (i.e. a bubble column), (ii) with a centric‐tube column and (iii) with a porous centric‐tube column. The specific growth rates (μ) of the batch cultures in the bubble column, the centric‐tube and the porous centric‐tube photobioreactor were 0.180, 0.226 and 0.252 day^?1, respectively. The porous centric‐tube photobioreactor, operated in semicontinuous culture mode with 10% CO₂ aeration, was evaluated. The results show that the maximum biomass productivity was 0.61 g/L when one fourth of the culture broth was recovered every 2 days. The CO₂ removal efficiency was also determined by measuring the influent and effluent loads at different aeration rates and cell densities of Chlorella sp. NCTU‐2. The results show that the CO₂ removal efficiency was related to biomass concentration and aeration rate. The maximum CO₂ removal efficiency of the Chlorella sp. NCTU‐2 culture was 63% when the biomass was maintained at 5.15 g/L concentration and 0.125 vvm aeration (volume gas per volume broth per min; 10% CO₂ in the aeration gas) in the porous centric‐tube photobioreactor.     

氧化铝气体分布器应用小球藻培养的研究

光生物反应器设计中,气体分布器对微藻生长有较大的影响,尤其是在鼓泡式光生物反应器中更为显著。实验考察了采用氧化铝烧制的多孔气体分布器的5L鼓泡式光生物反应器中通气速率、CO₂ 浓度对小球藻LICME002生物量、叶绿素含量、油脂积累的影响。对该气体分布器下的CO₂浓度和通气速率对小球藻的作用机理进行了初步的探讨。结果表明,CO₂浓度为3%时,该株微藻生物量、叶绿素、油脂积累的最佳;CO₂浓度超过6%时各项指标显著下降。通过对0.1vvm,0.4vvm,0.7vvm、1.0vvm的通气速条件下的各项指标的分析,确定最佳通气条件为0.4vvm。结论显示,在最佳通气速率和CO₂浓度下,微藻生物量能达到1.52g/L,油脂含量达到31.5%。     

Utilization of the cyanobacteria Anabaena sp. CH1 in biological carbon dioxide mitigation processes

Before switching totally to alternative fuel stage, CO₂ mitigation process has considered a transitional strategy for combustion of fossil fuels inevitably. In comparison to other CO₂ mitigation options, such as oceanic or geologic injection, the biological photosynthetic process would present a far superior and sustainable solution under both environmental and social considerations. The utilization of the cyanobacteria Anabaena sp. CH1 in carbon dioxide mitigation processes is analyzed in our research. It was found that an original developed photobioreactor with internal light source exhibits high light utilization. Anabaena sp. CH1 demonstrates excellent CO₂ tolerance even at 15% CO₂ level. This enables flue gas from power plant to be directly introduced to Anabaena sp. CH1 culture. Double light intensity and increased 47% CO₂ bubble retention time could enhance CO₂ removal efficiencies by 79% and 67%, respectively. A maximum CO₂ fixation rate of 1.01 g CO₂ L⁻¹ day⁻¹ was measured experimentally.     

Biofixation of CO2 from synthetic combustion gas using cultivated microalgae in three-stage serial tubular photobioreactors

Coal is the most abundant of the fossil fuels, with reserves estimated at 102 billions of tons. The feasibility of using coal as a fuel depends upon reducing emissions of gas when it is burnt, such as carbon dioxide (CO2), sulfur oxides (SO(x)), and nitrogen oxides (NO(x)). The removal of CO2 with microalgae may be one of the most efficient ways of reducing this gas, without the need for radical changes in the world's energy supply and production methods. Spirulina sp. LEB-18 and Scenedesmus obliquus LEB-22 were cultivated in serial tubular photobioreactors, with the aim of measuring the potential of CO2 biofixation and the resistance of the microalgae to SO2 and NO. Spirulina sp. and S. obliquus had CO2 biofixation scores of 0.27 and 0.22 g L(-1) d(-1), respectively. Both microalgae were resistant to SO2 and NO, and grew during the 15 d they were cultivated, which proves that using microalgae is an efficient method of biofixation of CO2 emitted when fossil fuels are burnt.     

利用啤酒废水小球藻异养培养

摘要：【目的】利用小球藻异养培养技术处理啤酒废水,旨在为啤酒废水资源化利用和降低小球藻生产成本提供一个途径。【方法】在含有10 g/L葡萄糖的基本培养基进行异养小球藻高效藻株的筛选,并用于啤酒废水的资源化处理。【结果】从5株小球藻中得到2株适合高密度异养培养的藻株（Chlorella pyrenoidosa 15-2070 和 Chlorella vulgaris 15-2075）,在啤酒废水的资源化处理过程中这2株小球藻得到非常接近的试验结果。利用由废水配制含10 g/L葡萄糖的基本培养液培养Chlorella pyrenoidosa 15-2070获得了5.3 g/L藻细胞;并且在此过程中,啤酒废水得到有效利用,几种主要污染物最高去除率为：CODcr,92.2 %;BOD5,95.1 %;NO3--N,98.5 %;NH4+-N,92.3 %。【结论】啤酒废水中的重要环境污染物在培养小球藻的过程中可以得到有效地清除,并从中可以获得具有商业价值的小球藻细胞。     

Photosynthetic performance of a helical tubular photobioreactor incorporating the cyanobacterium spirulina platensis

The photosynthetic performance of a helical tubular photobioreactor ("Biocoil"), incorporating the filamentous cyanobacterium Spirulina platensis, was investigated. The photobioreactor was constructed in a cylindrical shape (0.9 m high) with a 0.25-m(2)basal area and a photostage comprising 60 m of transparent PVC tubing of 1.6-cm inner diameter (volume = 12.1 L). The inner surface of the cylinder (area = 1.32 m(2)) was illuminated with cool white fluorescent lamps; the energy input of photosynthetically active radiation(PAR, 400 to 700 nm) into the photobioreactor was 2920 kJ per day. An air-lift system ncorporating 4%CO(2) was used to circulate the growth medium in the tubing. The maximum productivity achieved in batch culture was 7.18 g dry biomass per day [0.51 g . d biomass/L . day, or 5.44 g . d biomass/m(2)(inner surface of cylindrical shape)/day] which corresponded to a photosynthetic (PAR) efficiency of 5.45%. The CO(2) was efficiently removed from the gaseous stream; monitoring the CO(2) the outlet and inlet gas streams showed a 70% removal of CO(2) from the inlet gas over an 8-h period with almost maximum growth rate. (c) 1995 John Wiley & Sons, Inc.     

On the nitrogen and phosphorus removal in algal photobioreactors

This study shows results of nitrogen and phosphorus removal by microalgae (tertiary treatment) in a prototype of tubular photobioreactor tested under controlled and uncontrolled conditions. The wastewater was the supernatant coming from a secondary settler of a municipal wastewater activated sludge treatment plant without nitrification and denitrification units. The algal biomass was directly selected from the supernatant and it was principally composed of genus Scenedesmus (autochthonous algae). All the experiments evaluated both nitrogen and phosphorus removal and biomass and lipid production. A satisfactory nutrients removal - about 99.9% for the nitrogen and phosphorus - and a specific biomass productivity of 0.25 g/l d have been obtained in the indoor photobioreactor; less satisfactory results have been reached in the outdoor photobioreactor because of ambient condition instability and limiting nutrients concentration.     

Photosynthetic accumulation of carbon storage compounds under CO2 enrichment by the thermophilic cyanobacterium Thermosynechococcus elongatus

The growth characteristics of Thermosynechococcus elongatus on elevated CO? were studied in a photobioreactor. Cultures were able to grow on up to 20% CO?. The maximum productivity and CO? fixation rates were 0.09 ± 0.01 and 0.17 ± 0.01 mg ml?1 day?1, respectively, for cultures grown on 20% CO?. Three major carbon pools--lipids, polyhydroxybutyrates (PHBs), and glycogen--were measured. These carbon stores accounted for 50% of the total biomass carbon in cultures grown on atmospheric CO? (no supplemental CO?), but only accounted for 30% of the total biomass carbon in cultures grown on 5-20% CO?. Lipid content was approximately 20% (w/w) under all experimental conditions, while PHB content reached 14.5% (w/w) in cultures grown on atmospheric CO? and decreased to approximately 2.0% (w/w) at 5-20% CO?. Glycogen levels did not vary significantly and remained about 1.4% (w/w) under all test conditions. The maximum amount of CO? sequestered over the course of the nine-day chemostat experiment was 1.15 g l?1 in cultures grown on 20% CO?.     

Biological sulfate reduction using synthesis gas as energy and carbon source

Biological sulfate reduction was studied in laboratory-scale gas-lift reactors. Synthesis gas (gas mixtures of H(2)/CO/CO(2)) was used as energy and carbon source. The required biomass retention was obtained by aggregation and immobilization on pumice particles. Special attention was paid to the effect of CO addition on the sulfate conversion rate, aggregation, and aggregate composition.Addition of 5% CO negatively affected the overall sulfate conversion rate; i.e., it dropped from 12-14 to 6-8 g SO(2-) (4)/L day. However, a further increase of CO to 10 and 20% did not further deteriorate the process. With external biomass recycling the sulfate conversion rate could be improved to 10 g SO(2-) (4)/L day. Therefore biomass retention clearly could be regarded as the rate-limiting step. Furthermore, CO affected the aggregate shape and diameter. Scanning electron microscopy (SEM) photographs showed that rough aggregates pregrown on H(2)/CO(2) changed into smooth aggregates upon addition of CO. Addition of CO also changed the aggregate Sauter mean diameter (d(32)) from 1.7 mm at 5% CO to 2.1 mm at 20% CO. After addition of CO, a layered biomass structure developed. Acetobacterium sp. were mainly located at the outside of the aggregates, whereas Desulfovibrio sp. were located inside the aggregates. (c) 1996 John Wiley & Sons, Inc.     

Utilization of flue gas for cultivation of microalgae <Emphasis Type="Italic">Chlorella</Emphasis> sp.) in an outdoor open thin-layer photobioreactor

Flue gas generated by combustion of natural gas in a boiler was used for outdoor cultivation of Chlorella sp. in a 55 m² culture area photobioreactor. A 6 mm thick layer of algal suspension continuously running down the inclined lanes of the bioreactor at 50 cm s⁻¹ was exposed to sunlight. Flue gas containing 6–8% by volume of CO₂ substituted for more costly pure CO₂ as a source of carbon for autotrophic growth of algae. The degree of CO₂ mitigation (flue gas decarbonization) in the algal suspension was 10–50% and decreased with increasing flue gas injection rate into the culture. A dissolved CO₂ partial pressure (pCO₂) higher than 0.1 kPa was maintained in the suspension at the end of the 50 m long culture area in order to prevent limitation of algal growth by CO₂. NO_X and CO gases (up to 45 mg m⁻³ NO_X and 3 mg m⁻³ CO in flue gas) had no negative influence on the growth of the alga. On summer days the following daily net productivities of algae [g (dry weight) m⁻²] were attained in comparative parallel cultures: flue gas = 19.4–22.8; pure CO₂ = 19.1–22.6. Net utilization (η) of the photosynthetically active radiant (PAR) energy was: flue gas = 5.58–6.94%; pure CO₂ = 5.49–6.88%. The mass balance of CO₂ obtained for the flue gas stream and for the algal suspension was included in a mathematical model, which permitted the calculation of optimum flue gas injection rate into the photobioreactor, dependent on the time course of irradiance and culture temperature. It was estimated that about 50% of flue gas decarbonization can be attained in the photobioreactor and 4.4 kg of CO₂ is needed for production of 1 kg (dry weight) algal biomass. A scheme of a combined process of farm unit size is proposed; this includes anaerobic digestion of organic agricultural wastes, production and combustion of biogas, and utilization of flue gas for production of microalgal biomass, which could be used in animal feeds. A preliminary quantitative assessment of the microalgae production is presented.     

Simultaneous flue gas bioremediation and reduction of microalgal biomass production costs

A flue gas originating from a municipal waste incinerator was used as a source of CO₂ for the cultivation of the microalga Chlorella vulgaris, in order to decrease the biomass production costs and to bioremediate CO₂ simultaneously. The utilization of the flue gas containing 10–13% (v/v) CO₂ and 8–10% (v/v) O₂ for the photobioreactor agitation and CO₂ supply was proven to be convenient. The growth rate of algal cultures on the flue gas was even higher when compared with the control culture supplied by a mixture of pure CO₂ and air (11% (v/v) CO₂). Correspondingly, the CO₂ fixation rate was also higher when using the flue gas (4.4 g CO₂ l⁻¹ 24 h⁻¹) than using the control gas (3.0 g CO₂ l⁻¹ 24 h⁻¹). The toxicological analysis of the biomass produced using untreated flue gas showed only a slight excess of mercury while all the other compounds (other heavy metals, polycyclic aromatic hydrocarbons, polychlorinated dibenzodioxins and dibenzofurans, and polychlorinated biphenyls) were below the limits required by the European Union foodstuff legislation. Fortunately, extending the flue gas treatment prior to the cultivation unit by a simple granulated activated carbon column led to an efficient absorption of gaseous mercury and to the algal biomass composition compliant with all the foodstuff legislation requirements.     

CO2 biofixation and fatty acid composition of Scenedesmus obliquus and Chlorella pyrenoidosa in response to different CO2 levels

In this study, Scenedesmus obliquus SJTU-3 and Chlorella pyrenoidosa SJTU-2 were cultivated with 0.03%, 5%, 10%, 20%, 30%, 50% CO(2). The two microalgae could grow at 50% CO(2) (>0.69 g L(-1)) and grew well (>1.22 g L(-1)) under CO(2) concentrations ranging from 5% to 20%. Both of the two examined microalgae showed best growth potential at 10% CO(2). The maximum biomass concentration and CO(2) biofixation rate were 1.84 g L(-1) and 0.288 g L(-1) d(-1) for S. obliquus SJTU-3 and 1.55 g L(-1) and 0.260 g L(-1) d(-1) for C. pyrenoidosa SJTU-2, respectively. The main fatty acid compositions of the two examined microalgae were fatty acids with C(16)-C(18) (>94%) under different CO(2) levels. High CO(2) levels (30-50%) were favorable for the accumulation of total lipids and polyunsaturated fatty acids. The present results suggested that the two microalgae be appropriate for mitigating CO(2) in the flue gases and biodiesel production.     

微藻固定燃烧烟气中CO2 的研究进展

空气中CO2浓度升高导致的气候变暖问题已经成为全球性的环境、科学、政治、经济问题。近年来,对可用于直接固定工业废气尤其是燃烧烟气中CO2的捕捉和封存 (CCS) 技术进行了广泛的研究。在这些技术中,微藻生物固定CO2是一种具有大规模应用前景和经济上可行的CCS技术。以下从藻种的筛选、烟气条件对微藻固定CO2的影响、高效光生物反应器的开发和微藻产物的利用等方面对微藻生物固定烟气中CO2的现状和发展以及作者所在实验室在这一领域的研究情况进行了分析和总结,最后对其技术前景进行了展望,以期对微藻固定燃烧烟气中CO     

半连续及连续培养小球藻减排沼液及CO2

采用半连续或连续模式培养小球藻,考察小球藻减排沼液和CO2的能力。结果表明:在半连续培养模式中,当更新率为30%时,沼液中的N、P质量浓度可分别稳定在16～18和0.4～0.6 mg/L,达到污水二级排放标准;提高更新率到40%以上,3 d后微藻生物量及其对沼液中N、P的吸收达到动态平衡,但N、P去除率未达到污水直接排放标准;在连续培养模式中,分别选用20%及30%的日更新率,7 L规模12 d后沼液中的总氮(TN)仍高达55.64 mg/L。说明大规模培养条件下的光限制是微藻法减排沼液的主要制约因素。     

Improvement of mass transfer characteristics and productivities of inclined tubular photobioreactors by installation of internal static mixers

The feasibility of improving mass transfer characteristics of inclined tubular photobioreactors by installation of static mixers was investigated. The mass transfer characteristics of the tubular photobioreactor varied depending on the type (shape) and the number of static mixers. The volumetric oxygen transfer coefficient ( k(L)a) and gas hold up of the photobioreactor with internal static mixers were significantly higher than those of the photobioreactor without static mixers. The k(L)a and gas hold up increased with the number of static mixers but the mixing time became longer due to restricted liquid flow through the static mixers. By installing the static mixers, the liquid flow changed from plug flow to turbulent mixing so that cells were moved between the surface and bottom of the photobioreactor. In outdoor culture of Chlorella sorokiniana, the photobioreactor with static mixers gave higher biomass productivities irrespective of the standing biomass concentration and solar radiation. The effectiveness of the static mixers (average percentage increase in the productivities of the photobioreactor with static mixers over the productivities obtained without static mixers) was higher at higher standing biomass concentrations and on cloudy days (solar radiation below 6 MJ m(-2) day(-1)).     

不同种类无机盐对灰毡毛忍冬“渝蕾1号”悬浮培养体系中细胞生长和绿原酸含量的影响

为提高灰毡毛忍冬"渝蕾1号"悬浮培养体系中绿原酸的含量,该研究探讨了B_5培养基中不同浓度的无机盐对灰毡毛忍冬"渝蕾1号"悬浮培养细胞生物量及绿原酸含量的影响,通过在悬浮培养体系中添加不同浓度的无机盐,采用重量法测定灰毡毛忍冬"渝蕾1号"悬浮培养细胞的生物量及采用高效液相色谱法测定绿原酸的含量。结果表明:当硝态氮和铵态氮配比与B_5培养基中硝态氮和铵态氮配比一致时,即NO_3~-/NH_4~+摩尔比值为13∶1时,培养体系有利于细胞的生长和绿原酸的积累。当KNO_3浓度为3.5 g·L~(-1)时,细胞生物量达到最大,为19.26 g·L~(-1);当KNO_3在较低浓度(0.5 g·L~(-1)和1.5 g·L~(-1))时,积累较多的绿原酸。NO_3~-的两项研究结果均与对照浓度(2.5g·L~(-1))有一定的差异。另外,对(NH_4)_2SO_4来说,在高于对照浓度0.134 g·L~(-1),即浓度为0.268 g·L~(-1)时,生物量和绿原酸含量都达到了最大。P、Ca、Mg三种矿质元素的研究结果表明,当Na H_2PO_4·2H_2O浓度为0.10 g·L~(-1)、Ca Cl_2的浓度为0.20 g·L~(-1)时,细胞的生长和绿原酸的积累均可达到最大值;而对Mg~(2+)来说,低浓度促进细胞的生长,高浓度促进绿原酸的积累。兼顾细胞生物量和绿原酸含量两个指标,需选择适中的浓度。这些结果均与对照浓度有一定的差异。这说明灰毡毛忍冬"渝蕾1号"悬浮细胞所需无机盐的浓度与B_5培养基无机盐的浓度有一定的差异,选择适宜的浓度可促进其悬浮细胞的生长及次生代谢产物绿原酸的积累。该研究结果为绿原酸的工业化生产打下了基础。