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.     

氮源种类及浓度对眼点拟微绿球藻生长密度、油脂产率和二十碳五烯酸含量的影响

氮源是影响微藻生长和油脂积累的重要因素,文中通过单因素试验比较了NaNO3、CO(NH2)2、NH4Cl、CH3COONH4及其浓度对眼点拟微绿球藻生长密度、生长速率、油脂产率、二十碳五烯酸(EPA)含量的影响。结果表明：NH4+更易被眼点拟微绿球藻利用,能更好地促进微藻生长和油脂积累;氮浓度的增加有利于微藻的生长和藻油脂肪酸的去饱和,但不利于微藻油脂的积累。在实验考察的氮源种类和浓度范围内,CH3COONH4是促进眼点拟微绿球藻生长和油脂积累、EPA生成的适宜氮源,其适宜的浓度为5.29 mmol/L。     

产油微藻自养培养条件调控

作为新兴生物燃料的生物柴油近年来发展迅速,以微藻为代表的第二代生物能源是解决能源危机的长远之计,但如何提高其产量仍是研究的热点问题。以提高产油自养微藻生物量和油脂含量为目的,在气升式光反应器中运用均匀设计实验方法进行了条件优化试验。分别得出了氮原子浓度、通气速率、二氧化碳体积浓度和光照强度4个因素对小球藻C2生物量积累和油脂含量影响的显著回归方程和反应器优化培养条件。以生物量为指标的优化培养条件是:氮原子浓度0.178 g/L,通气速率5 L/min,二氧化碳体积浓度3%(V/V),光照强度6000 lx。该优化条件下,生物量为2.11 g/L,即生产速率为0.352 g/(L.d),比测试实验中检测到的最高生物量[1.88 g/L,即生产速率为0.313 g/(L.d)]提高了12.2%;以油脂含量为指标的优化培养条件是:进气速率0.400 L/min,二氧化碳体积浓度1.94%(V/V),得到油脂含量为22.4%,比测试实验中检测到的最高油脂量(20.7%)提高7.7%。     

Microalgal biomass production and on-site bioremediation of carbon dioxide, nitrogen oxide and sulfur dioxide from flue gas using Chlorella sp. cultures

The growth and on-site bioremediation potential of an isolated thermal- and CO?-tolerant mutant strain, Chlorella sp. MTF-7, were investigated. The Chlorella sp. MTF-7 cultures were directly aerated with the flue gas generated from coke oven of a steel plant. The biomass concentration, growth rate and lipid content of Chlorella sp. MTF-7 cultured in an outdoor 50-L photobioreactor for 6 days was 2.87 g L?1 (with an initial culture biomass concentration of 0.75 g L?1), 0.52 g L?1 d?1 and 25.2%, respectively. By the operation with intermittent flue gas aeration in a double-set photobioreactor system, average efficiency of CO? removal from the flue gas could reach to 60%, and NO and SO? removal efficiency was maintained at approximately 70% and 50%, respectively. Our results demonstrate that flue gas from coke oven could be directly introduced into Chlorella sp. MTF-7 cultures to potentially produce algal biomass and efficiently capture CO?, NO and SO? from flue gas.     

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.     

Chlorella stigmatophora for urban wastewater nutrient removal and CO2 abatement

Batch experiments were performed to study biomass growth rate, nutrient removal and carbon dioxide bio-fixation of the marine microalgae Chlorella stigmatophora. Four different cultures at different salinities were tested: wastewater (WW), synthetic wastewater (SWW), seawater (SW) and diluted seawater (DSW). Experimental results showed that Chlorella stigmatophora grew satisfactorily in all culture media, except in SWW where inhibition occurred. In all cases, biomass experimental data were fitted to the Verlhust Logistic model (R2 > 0.982, p < or = 0.05). Maximum biomass productivity (P(bmax)) and CO2 biofixation (P(vCO2)) were reached in the WW medium, 1.146g SSL(-1)day(-1) and 2.324g CO2L(-1)day(-1) respectively. The order of maximum specific growth rates (micro max) was WW >DSW>SW. In order to compare nitrogen and phosphorous removal kinetics, an estimation of the time required to reach the most restrictive concentration of total N and P in effluents as defined in the Directive 98/1565/CE (10 mg sigmaNL(-1) (T10(N)) and 1 mg sigmaPL(-1) (T1(p)) was performed. In the WW test T10(N) and T1(p) needed were of 45.15 and 32.27 hours respectively and at the end of the experimental the removal was in both 100%.     

Optimized aeration by carbon dioxide gas for microalgal production and mass transfer characterization in a vertical flat-plate photobioreactor

To optimize the aeration conditions for microalgal biomass production in a vertical flat-plate photobioreactor (VFPP), the effect of the aeration rate on biomass productivity was investigated under given conditions. Air enriched with 5% or 10% (v/v) CO(2) was supplied for the investigation at rates of 0.025-1 vvm. The CO(2) utilization efficiency, change of pH in the medium, and the optimum aeration rate were determined by evaluating biomass productivity. To investigate the VFPP mass transfer characteristics, the overall volumetric mass transfer coefficient, k(L)a, was evaluated for several different flat-plate sizes. Increasing the height of the VFPP could improve both the mass transfer of CO(2) and the illumination conditions, so this appeared to be a good method for scaling up. Based on a comparison of the k(L)a value at the optimum aeration rate with previously reported results, it was confirmed that the range of CO(2) concentration used in the experiments was cost-effective for mass culture.     

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.     

Serial optimization of biomass production using microalga Nannochloris oculata and corresponding lipid biosynthesis

As energy and environment have become urgent issues, there has been increasing needs to develop alternative energy source, such as microalgal bio-fuel. In this study, we investigated the growth and lipid contents of microalgae Nannochloris oculata under various environmental conditions for biodiesel production. Our results indicated that biomass productivities of N. oculata were correlated with increasing nitrogen concentrations up to 37.5 ppm. High irradiance using 230-250 μmol/m(2) led to higher biomass yields than low irradiance of 160-180 μmol/m(2). Biomass productivities increased further by manipulating surface to volume ratio (S/V), which in turn enhanced light penetration. Finally, optimal biomass productivities (1.04 g/l day) could be achieved by the supplementation of yeast extract. Lipid contents and fatty acid profiles of N. oculata were affected by the different growth conditions. Lipid contents of N. oculata decreased as nitrogen concentration increased. Lower temperature (15 °C) resulted in higher lipid content than higher temperature (25 °C). Fatty acid profiles of N. oculata indicated that palmitic acid (C16:0) and linoleic acid (C18:2) were the two most abundant fatty acids, but the supplementation of yeast extract increased linolenic acid (C18:3) content. Our results suggested the feasibility of N. oculata for the biodiesel production.     

Cultivation of microplantlets derived from the marine red alga Agardhiella subulata in a stirred tank photobioreactor

Macrophytic marine red algae are a diverse source of bioactive natural compounds. "Microplantlet" suspension cultures established from red algae are potential platforms for biosynthesis of these compounds, provided suitable bioreactor configurations for mass culture can be identified. The stirred tank bioreactor offers high rates of gas-liquid mass transfer, which may facilitate the delivery of the CO(2) in the aeration gas to the phototrophic microplantlet suspension culture. Therefore, the effects of impeller speed and CO(2) delivery on the long-term production of microplantlet biomass of the model red alga Agardhiella subulata was studied within a stirred tank photobioreactor equipped with a paddle blade impeller (D(i)/D(T) = 0.5). Nutrient medium replacement was required for sustained biomass production, and the biomass yield coefficient based on nitrate consumption was 1.08 +/- 0.09 g dry biomass per mmol N consumed. Biomass production went through two exponential phases of growth, followed by a CO(2) delivery limited growth phase. The CO(2)-limited growth phase was observed only if the specific growth rate in the second exponential phase of growth was at least 0.03 day(-)(1), the CO(2) delivery rate was less than 0.258 mmol CO(2) L(-)(1) culture h(-)(1), and the plantlet density was at least 10 g fresh mass L(-)(1). Increasing the aeration gas CO(2) partial pressure from 0.00035 to 0.0072 atm decreased the cultivation pH from 8.8 to 7.8, prolonged the second exponential phase of growth by increasing the CO(2) delivery rate, and also increased the photosynthetic oxygen evolution rate. Impeller speeds ranging from 60 to 250 rpm, which generated average shear rates of 2-10 s(-)(1), did not have a significant effect on biomass production rate. However, microplantlets cultivated in a stirred tank bioreactor ultimately assumed compact spherical shape, presumably to minimize exposure to hydrodynamic stress.     

Growth, nitrogen uptake, and metabolism in two semiarid shrubs grown at ambient and elevated atmospheric CO2 concentrations: effects of nitrogen supply and source

The effect of differences in nitrogen (N) availability and source on growth and nitrogen metabolism at different atmospheric CO(2) concentrations in Prosopis glandulosa and Prosopis flexuosa (native to semiarid regions of North and South America, respectively) was examined. Total biomass, allocation, N uptake, and metabolites (e.g., free NO(3)(-), soluble proteins, organic acids) were measured in seedlings grown in controlled environment chambers for 48 d at ambient (350 ppm) and elevated (650 ppm) CO(2) and fertilized with high (8.0 mmol/L) or low (0.8 mmol/L) N (N(level)), supplied at either 1 : 1 or 3 : 1 NO(3)(-) : NH(4)(+) ratios (N(source)). Responses to elevated CO(2) depended on both N(level) and N(source), with the largest effects evident at high N(level). A high NO(3)(-) : NH(4)(+) ratio stimulated growth responses to elevated CO(2) in both species when N was limiting and increased the responses of P. flexuosa at high N(level). Significant differences in N uptake and metabolites were found between species. Seedlings of both species are highly responsive to N availability and will benefit from increases in CO(2), provided that a high proportion of NO(3)- to NH(4)-N is present in the soil solution. This enhancement, in combination with responses that increase N acquisition and increases in water use efficiency typically found at elevated CO(2), may indicate that these semiarid species will be better able to cope with both nutrient and water deficits as CO(2) levels rise.     

CO2浓度升高与氮添加对三江平原湿地小叶章生长的影响

利用开顶箱薰气室,设置正常大气CO₂浓度(350 μmol·mol^-1)、高CO₂浓度(700 μmol·mol^-1)2个CO₂水平和不施氮(0 g N·m^-2)、中氮(5 g N·m^-2)和高氮(15 g N·m^-2)3个氮素水平,研究CO₂浓度升高和氮肥施用对三江平原草甸小叶章生长的影响.结果表明：随着CO₂浓度升高,小叶章物候期提前,其中抽穗期提前1～2 d,成熟期提前3 d;不施氮、中氮和高氮水平下, CO₂浓度升高使小叶章的分蘖分别增加8.2%(P<0.05)、8.4%(P<0.05)和5.5%(P>0.05);在小叶章生长初期,CO₂浓度升高对其生物量的增加有促进作用,拔节期和抽穗期小叶章地上生物量分别增加12.4%和20.9%(P<0.05);生长后期则对小叶章地下生物量的促进作用增大,腊熟期和成熟期的地下生物量分别增加20.5%和20.9% (P<0.05).小叶章生物量对高浓度CO₂的响应与供氮水平有关,供氮充足条件下, 高浓度CO₂对生物量的促进效应更大.     

碳源种类及碳氮比对眼点拟微绿球藻生长密度、油脂含量和脂肪酸组成的影响

研究了三种碳源Na2CO3、NaHCO3、葡萄糖对眼点拟微绿球藻生长密度和油旨含量的影响,实验结果表明相对于葡萄糖,无机碳源NaHCO3更利于眼点拟微绿球藻的生长.以NaHCO3为碳源,研究了在不同的接种密度、NaNO3浓度下,C/N对眼点拟微绿球藻生长密度和油脂含量的影响.实验结果表明,C/N对眼点拟微绿球藻生长密度的影响与接种密度和NaNO3浓度有关,在高的NaNO3浓度时,C/N对眼点拟微绿球藻生长密度的影响很小;在低的NaNO3浓度时,随着C/N比的增加,微绿球藻的生长密度先增加后下降,存在最佳的C/N比.最佳的C/N比随接种密度而变化,在接种密度为OD440=0.10时,最佳C/N比为3,当接种密度提高到OD440=0.70时,最佳C/N比增加到5.NaNO3浓度和C/N对微藻油脂含量均有较大影响,在不同的接种密度和NaNO3浓度下都表现为C/N=1时最利于微藻油脂的积累,这与卡尔文循环过程中核酮糖-1,5-二磷酸羧化酶/加氧酶的活性有关.本实验的最佳产油培养条件为以NaHCO3为碳源,初始接种密度为OD440=0.70,C/N=1∶1,CNaNO3=0.225g/L,此时油脂产率为56.7 mg/(L·d),EPA产率为6.5 mg/(L·d).     

A new combined approach to improved lipid production using a strictly aerobic and oleaginous yeast

Microbial lipids have potential applications in energy, and food industry, because most of those lipids are triacylglycerol with long‐chain fatty‐acids that are comparable to conventional vegetable oils and can be obtained without arable land requirement. Rhodosporidium toruloides is a strictly aerobic strain, where oxygen plays a crucial role in growth, maintenance, and metabolite production, such as lipids and carotenoids. Dissolved oxygen concentration is one of the major factors affecting yeast physiological and biochemical characteristics. In this context, different approaches have been developed to increase available oxygen by the increasing the aeration and the addition of an oxygen‐vector. The growth of R. toruloides in 2‐L mechanical stirred tank reactor equipped with 1 or 2 porous spargers and a 70 C/N ratio, revealed a lipid content of 0.47 and 0.52 g/g and a lipidic productivity of 0.16 and 0.17 g/L day, respectively. The oxygen‐vector addition, increased the lipidic productivity for 0.20 g/L day and a lipid contend of 0.51 g of lipids/g of biomass. The combined approach, combining high aeration (AA), and 1% of n‐dodecane addition (DA), produced a significant improvement in the lipid accumulation (62%, w/w), when compared with the DA (51%, w/w) and the AA (52%, w/w) approaches. The increasing of lipids accumulation and smaller culture time are key factors for the success of scale‐up and profitability of a bioprocess.     

富油能源微藻的筛选及产油性能评价

为了筛选具有产油潜力的能源微藻,以实验室保藏的20株淡水和海洋微藻(绿藻门18株,真眼点藻纲1株,硅藻纲1株)为研究对象,利用光径为3 cm柱状光生物反应器通气分批培养,通过测定微藻培养物的生物量和总脂含量等指标,从中筛选生长速度快、生物量和总脂含量高的微藻。结果表明:20株微藻的生物量和总脂含量分别在1.81~7.88g/L和16.0%~55.9% dw(% Dry weight)之间,筛选得到具有产油潜力的微藻9株,分别是栅藻(Scenedesmus sp.)(6.34g/L,55.9% dw)、麻织绿球藻(Chlorococcum tatrense)(5.93g/L,46.9% dw)、眼点拟微绿球藻(Nannochloropsis oculata)(7.88g/L,35.0% dw)、油面绿球藻(Chlorococcum oleofaciens)(5.58g/L,45.9% dw)、多形拟绿球藻(Pseudochlorococcum polymorphum)(6.10g/L,40.0% dw)、八月衣藻(Chlamydomonas augustae)(5.78g/L,40.5% dw)、椭圆小球藻(Chlorella ellipsoidea)(5.56g/L,40.7%dw)、椭圆绿球藻(Chlorococcum ellipsoideum)(5.41g/L,38.0% dw)、雪绿球藻(Chlorococcum nivale)(5.55g/L,36.3% dw),其中最具产业化潜力的微藻为栅藻(Scenedesmus sp.),其总脂收获量和单位体积总脂产率分别为3.5 g/L和218.7mg/L·d。     

Performance of a sulfide-oxidizing expanded-bed reactor supplied with dissolved oxygen

The performance of a new sulfide-oxidizing, expanded-bed bioreactor is described. To stimulate the formation of well-settleable sulfur sludge, which comprises active sulfide-oxidizing bacterial biomass and elemental sulfur, the aeration of the liquid phase and the oxidation of sulfide to elemental sulfur are spatially separated. The liquid phase is aerated in a vessel and subsequently recirculated to the sulfide-oxidizing bioreactor. In this manner, turbulencies due to aeration of the liquid phase in the bioreactor are avoided. It appeared that, under autotrophic conditions, almost all biomass present in the reactor will be immobilized within the sulfur sludge which consists mainly of elemental sulfur (92%) and biomass (2.5%). The particles formed have a diameter of up to 3 mm and can easily be grinded down. Within time, the sulfur sludge obtained excellent settling properties; e.g., after 50 days of operation, 90% of the sludge settles down at a velocity above 25 m h(-1) while 10% of the sludge had a sedimentation velocity higher than 108 m h(-1). Because the biomass is retained in the reactor, higher sulfide loading rates may be applied than to a conventional "free-cell" suspension. The maximum sulfide-loading rate reached was 14 g HS(-) L(-1) d(-1), whereas for a free-cell suspension a maximum loading rate of 6 g HS(-) L(-1) d(-1) was found. At higher loading rates, the upward velocities of the aerated suspension became too high so that sulfur sludge accumulated in the settling zone on top of the reactor. When the influent was supplemented with volatile fatty acids, heterotrophic sulfur and sulfate reducing bacteria, and possibly also (facultatively) heterotrophic Thiobacilli, accumulated within the sludge. This led to a serious deterioration of the system; i.e., the sulfur formed was increasingly reduced to sulfide, and also the formation rate of sulfur sludge declined. (c) 1997 John Wiley & Sons, Inc.     

Dilution of solar radiation through "culture" lamination in photobioreactor rows facing south-north: a way to improve the efficiency of light utilization by cyanobacteria (Arthrospira platensis)

Efficient utilization of solar radiation for the photoautotrophic production of cyanobacterium biomass was achieved, using small pipes (ID = 0.01 m) arranged in rows in two photobioreactors facing south-north. A high Arthrospira yield of 47.7 g m(-2) (installation area) d(-1) was attained under outdoor conditions in a tubular undulating row photobioreactor (TURP-10r). During the summer, under a semicontinuous culture regime, the optimal biomass concentration (OBC) in TURP-5r was 6.0 g L(-1): it was 5.0 g L(-1) in TURP-10r. These OBCs made it possible to produce a biomass output rate of 2.7 +/- 0.2 g L(-1) d(-1) in the former and 2.1 +/- 0.1 g L(-1) d(-1) in the latter. When Arthrospira was grown at a preset dilution rate (0.3 d(-1)), sunrise cell density (SrCD) variations were not proportional to the drop of solar radiation. The SrCD was comparatively high at high solar radiation and decreased abruptly with decreasing solar radiation. There was a tendency to stabilize at low solar radiation. In both photobioreactors, the chlorophyll content of the Arthrospira biomass (% of the dry weight) was higher at sunrise than at sunset. A comparison of the chlorophyll biomass content in the TURPs showed no significant differences. Night biomass losses were very high (> 30% of the daylight productivity) when the culture temperature was kept constant at 31 +/- 1.0 degrees C: these losses fell to < 20% of the daylight productivity, when the night temperature of the cultures decreased according to the environmental temperature. Dilution of solar radiation was carried out using two quasi-laminated bioreactors. The rows of S-N facing bioreactors showed a very high growth yield in TURP-10r [about 2.1g (d.w.) MJ(-1)]. In TURP-10r, the high photic ratio (R(f) = 6), the high surface-to-volume ratio (S(ill)/V = 400 m(-1)) and the S-N facing of the rows (better than an E-W orientation) allowed for good results.     

Nitrogen starvation strategies and photobioreactor design for enhancing lipid content and lipid production of a newly isolated microalga Chlorella vulgaris ESP-31: implications for biofuels

Microalgae are recognized for serving as a sustainable source for biodiesel production. This study investigated the effect of nitrogen starvation strategies and photobioreactor design on the performance of lipid production and of CO(2) fixation of an indigenous microalga Chlorella vulgaris ESP-31. Comparison of single-stage and two-stage nitrogen starvation strategies shows that single-stage cultivation on basal medium with low initial nitrogen source concentration (i.e., 0.313 g/L KNO(3)) was the most effective approach to enhance microalgal lipid production, attaining a lipid productivity of 78 mg/L/d and a lipid content of 55.9%. The lipid productivity of C. vulgaris ESP-31 was further upgraded to 132.4 mg/L/d when it was grown in a vertical tubular photobioreactor with a high surface to volume ratio of 109.3 m(2)/m(3) . The high lipid productivity was also accompanied by fixation of 6.36 g CO(2) during the 10-day photoautotrophic growth with a CO(2) fixation rate of 430 mg/L/d. Analysis of fatty acid composition of the microalgal lipid indicates that over 65% of fatty acids in the microalgal lipid are saturated [i.e., palmitic acid (C16:0) and stearic acid (C18:0)] and monounsaturated [i.e., oleic acid (C18:1)]. This lipid quality is suitable for biodiesel production.     

稻草覆盖对冬闲稻田二氧化碳通量的影响

通过研究稻草覆盖对土壤含水量、土壤温度及田间杂草生长的影响,探讨了亚热带红壤性稻田生态系统冬闲期稻草覆盖对CO2通量的影响及其机理.结果表明:稻草覆盖主要通过两个途径影响冬闲稻田的CO2通量:一是稻草覆盖对土壤温度有正效应,使稻田生态系统CO2排放量显著增加,试验期间覆盖处理平均净排放1.99 g CO2·m-2·d-1,而对照处理平均净吸收2.68 g CO2·m-2·d-1,两者差异达极显著水平(P《0.01);二是稻草覆盖使田间杂草的生物量及其吸收的光合有效辐射显著减少, 导致覆盖处理白天CO2排放量提高.稻草覆盖处理土壤表层(0～15 cm)相对含水量比无覆盖处理提高了9%以上,但未对CO2通量的变化产生显著影响.     

Investigation of continuous-batch mode of two-stage culture of Nannochloropsis sp. for lipid production

Microalgal lipid induction through nitrogen stress often suffers from a contradiction between biomass productivity and lipid content, i.e., either high biomass productivity with low lipid content or vice versa. A two-stage nitrogen-replete and nitrogen-deplete (NR–ND) culture was suggested to be an option to attain high lipid productivity. In this study, the effects of culture conditions and modes on biomass productivity and lipid productivity of Nannochloropsis sp. in the two stages were comprehensively investigated. The optimal culture conditions for the two stages, aiming to high biomass productivity and lipid productivity respectively, were consistent, i.e., CO₂ content in aeration (1 %), phosphorus concentration in medium (181 μmol/L), incident light intensity (150 μE/(m²s)), temperature (25 °C). Different culture modes of the two stages were compared. The overall lipid productivity of the two-stage continuous-batch mode achieved 0.123 g/(L day), which was 60.3, 48.2, 34.9 and 13.5 % higher than that of single nitrogen-replete batch, single nitrogen-limited batch, continuous nitrogen-replete culture and two-stage batch–batch culture, respectively, and also higher than most reported values. This contribution provides fundamental data for the two-stage NR–ND cultivation process design of Nannochloropsis sp.