CO_2对可沉微藻油脂含量的影响

作为一种光合自养微生物,微藻可以利用无机碳源和氮、磷在其细胞体内合成淀粉、多糖、蛋白质,甚至是油脂。然而,微藻与液体分离通常十分困难,否则,水体富营养化现象很容易得到解决。事实上,藻类中存在着可以自然沉降的种属,只不过在自然环境下难以成为优势种属。在实验室条件下,通过"冲淘"压力可以筛选出沉淀性能非常好的可沉藻,使培养藻类沉淀效率高达97%(SVI=17 m L/g)。问题是所培养出的可沉微藻种属油脂含量不高,不具有能源回收价值。为此,在前期富集培养出可沉藻基础上,采用通入CO_2(5%)方式刺激藻类生长,并试图获得较高的藻细胞油脂含量。间歇试验表明,通入CO2可提高产油微藻(硅藻、绿藻)的稳定性,延长微藻增长时间(35 d→56 d),获得较高叶绿素a含量(5.3 mg/L→6.4 mg/L),强化污水脱氮除磷效率,增加藻细胞油脂(11.21%)、多糖(7.20%)含量。     

可沉微藻对室外光照强度的适应性试验研究

在实验室条件下,通过"冲淘"压力可筛选出沉淀率高达97%的可沉微藻。可沉微藻像活性污泥一样在净化功能完成后可通过自然沉降实现藻-水分离,可为污水深度处理提供一种低耗、高效的解决方案。然而,实验室低光照[400μmol/(m^2·s)]条件下获得的可沉微藻在真实自然光强度下是否依然可以不断生长繁殖并保持对氮、磷较高的去除率,这是一个工程应用必须面对的现实问题。为此,在实验室条件下增加光照强度至接近自然光水平[800μmol/(m^2·s)],观察可沉微藻的生长情况。结果显示,高光照强度对可沉微藻具有抑制作用,使可沉微藻的生长繁殖严重受阻,并降低其光合作用活性(叶绿素a含量)。及时向反应器补充无机碳源CO_2后,可沉微藻经过一定适应期后可恢复生长,并可达到比低光照强度时还高的生物量及较高的氮、磷去除效果(90%以上)。另外,试验还考察了投加营养物硅酸盐、光/暗交替及进水模式对可沉微藻生长与净化性能的影响,结果显示出硅酸盐的双向性作用及光补充基质的优势。     

微藻油脂含量不同测定方法的比较研究

为了对微藻油脂含量不同测定方法进行比较,以球等鞭金藻8701 Isochrysis galbana Parke 8701和小新月菱形藻Nitzschia closterium f.minutissima两种微藻为研究对象,采用溶剂提取法和苏丹黑B染色法对其油脂含量进行测定,建立了两种微藻油脂含量与苏丹黑染色后吸光度A645 nm的线性回归方程,并应用于微藻油脂积累培养过程的快速测定,利用气相色谱法对两种微藻脂肪酸组成进行分析。结果表明:当提取溶剂为二氯甲烷和甲醇的混合溶剂(二者的体积比为1∶2)时,油脂提取效果较好,得到球等鞭金藻8701和小新月菱形藻的油脂含量分别为22.99%和16.89%;采用苏丹黑B染色法测定的油脂含量基本和生物量大体一致,是一种可行的估测油脂含量的方法;气相色谱检测结果显示,两种微藻具有明显不同的脂肪酸组成特征,球等鞭金藻8701的饱和脂肪酸含量(55.02%)较小新月菱形藻(51.39%)高。研究表明,从两种微藻的油脂含量和脂肪酸组成来看,球等鞭金藻8701较小新月菱形藻更适用于作为生物柴油的原料。     

大气CO_2浓度升高对大型海藻孔石莼生长和色素含量的影响

在实验室模拟研究了大气CO2浓度升高对海洋中大型绿藻孔石莼Ulva pertusa的生长和色素含量的影响。设置4个独立试验,每个试验的CO2浓度分别为387、500、600、800 mg/L。每个试验设6个海水培养系统,其中3个通入一定浓度的CO2作为试验系统,另外3个通入大气作为对照系统。在每个海水培养系统中,分别装入25 L过滤海水(滤膜孔径为0.22μm),放入(50.0±1.0)g的孔石莼进行培养,试验进行7 d。结果表明:高浓度CO2对孔石莼生长无显著影响(P>0.05),但降低了孔石莼中叶绿素a和类胡萝卜素的含量;试验结束时,CO2浓度为387、500、600、800 mg/L时,试验系统中孔石莼的叶绿素a含量分别为(855.9±31.6)、(780.8±6.2)、(677.3±22.1)、(585.1±16.9)μg/g(鲜质量),分别为对照系统的98.3%、91.8%、78.4%和71.7%,试验系统中孔石莼的类胡萝卜素含量分别为(185.6±5.0)、(167.8±2.4)、(150.6±2.3)、(128.3±4.3)μg/g(鲜质量),分别为对照系统的97.7%、91.5%、80.4%和69.4%;而对照系统中试验开始时和试验结束时,孔石莼的叶绿素a含量和类胡萝卜素含量均无显著性差异(P>0.05)。     

硫氰酸红霉素原位杀藻的生态学效应

为明确杀藻剂作用下生态围隔内蓝藻及微囊藻丰度、底泥微囊藻毒素(MCs)含量及关键水化学指标的动态变化规律,在蓝藻水华暴发期的淡水鱼类养殖尾水循环渠中,开展了硫氰酸红霉素原位杀藻的生态学效应研究。试验设置4个浓度(0.25、0.5、1、2 mg/L)的硫氰酸红霉素处理组和1个未添加硫氰酸红霉素的对照组,每组设3个平行,试验共进行10 d。结果表明:硫氰酸红霉素对生态围隔内蓝藻及微囊藻具有强烈的抑杀效应,试验结束时对蓝藻及微囊藻抑杀率均达99%以上;硫氰酸红霉素作用过程中生态围隔内底泥MCs含量呈现明显的先升高后降低趋势,最高值出现在第2天,MC-RR含量为2.58μg/g,MC-LR含量为3.39μg/g;使用硫氰酸红霉素应急抑杀蓝藻后,水体中NO_2^--N、NO_3--N、NO_3^--N、NH_4--N、NH_4⁺-N及COD_(Mn)含量短时间内均有不同程度地提高,其中尤以NH_4+-N及COD_(Mn)含量短时间内均有不同程度地提高,其中尤以NH_4⁺-N与COD_(Mn)含量升高较为明显。综合考虑杀藻效果、底泥中MCs储积量及关键水化学指标变化规律,建议养殖生产中使用≤0.25 mg/L硫氰酸红霉素应急杀灭蓝藻,并在抑杀蓝藻后及时增氧、泼洒解毒剂及微生态制剂。     

碳源、氮源对异养单针藻Monoraphidium sp.FXY-10油脂积累和脂肪酸组成的影响

研究了碳源与氮源对单针藻Monoraphidium sp.FXY-10异养培养的影响。以BG-11为基础培养基,通过添加不同类型、浓度梯度碳源和氮源,比较分析微藻生物量、油脂积累以及脂肪酸组成。结果表明,以葡萄糖作碳源,硝酸钠为氮源,微藻细胞积累的油脂是理想的生物柴油制备原料。硝酸钠浓度分别为1.00、3.00和5.00 g/L时,对油脂产量影响不显著(P>0.05)。葡萄糖浓度为10.00 g/L,硝酸钠为氮源油脂产量达到实验最高值0.84 g/L,其油脂脂肪酸组成主要由C16∶0和C18∶1等短链饱和脂肪酸和单不饱和脂肪酸组成,不饱和度值(DU)为61.98,相对偏低。     

基于机械淘洗的活性初沉池碳源转化与回收评价

针对我国污水处理厂进水碳氮比值失调、初沉池中颗粒态碳源流失严重导致生物系统脱氮除磷碳源不足的问题,开展了传统初沉池运行效果评价与活性初沉池碳源转化回收技术研究。结果表明,传统初沉池对COD的去除率达到40.49%,其中对颗粒态COD的去除率更是高达56.27%,初沉池中大量碳源的无效流失导致生物系统进水碳氮比值与碳磷比值明显降低。而在活性初沉池中试系统中,由于大量污泥在池底部长期积累,有利于水解发酵细菌的繁殖与富集。高通量测序分析结果显示,Proteobacteria(34.17%)、Bacteroidetes(22.22%)、Chloroflexi(13.29%)是活性初沉池系统中的优势种群。活性初沉池系统使初沉污泥中微生物种群结构发生了显著的变化,而这种变化有利于初沉污泥水解发酵的进行。通过微生物的水解发酵及机械搅拌单元的淘洗作用,活性初沉池出水SCOD与VFAs可分别增加51.7 mg/L和18.8 mg/L,经过活性初沉池后污水的SCOD/TN值和SCOD/TP值可分别提高40.9%和41.8%。活性初沉池系统可有效减少污水中碳源流失,实现对颗粒态碳源的原位转化与回收。     

乙酸钠碳源强化生物滤池对二沉池出水的脱氮效果

对于碳源不足的城市污水厂二沉池出水,通过外加碳源提高对其TN的去除率是一种直接而有效的方法.采用生物滤池(滤速为2 m/h)深度处理二沉池出水,并投加乙酸钠碳源,发现当进水混合液的COD>95.0 mg/L时,对TN的去除率可达到98%;部分外加碳源可被DO消耗,只有当进水混合液COD增至57.7 mg/L时,出水DO降到0.8 m/L左右,反硝化现象才逐渐明显;当碳源投加不足时,会出现亚硝态氮的积累,当进水混合液的COD平均为81.1mg/L时,亚硝态氮积累量高达6 mg/L.     

丙酸/乙酸比值对反硝化除磷的影响

分别以丙酸、丙酸/乙酸(浓度比值为0.5、2)、乙酸为碳源,在SBR中采用厌氧/缺氧方式驯化富集反硝化聚磷菌(DPB),研究了丙酸/乙酸比值对反硝化除磷系统中有机物的降解、PO3-4-P的释放与吸收、NO-x-N浓度、PHB和糖原含量以及污泥中磷含量的影响.结果表明,随着丙酸/乙酸比值的提高,厌氧释磷量减少,厌氧末期的PHB含量降低,缺氧段聚磷菌的合成和代谢能力减弱,最终导致对PO3-4-P的去除率降低.因此,乙酸含量高的碳源更利于反硝化除磷的进行.     

“异养-胁迫”分段培养对原始小球藻生物量和油脂含量影响研究

在"异养-胁迫"分段培养模式下分析原始小球藻(Chlorella protothecoides)的生物量及油脂含量。结果表明,在500ml摇瓶中,分段培养生物量达5.32g/L,略低于一步异养培养5.45 g/L,油脂含量达34.81%,是一步异养培养的2.26倍,藻渣中微藻多糖含量由9.57%提高到18.06%。在3L发酵罐中,一步异养培养模式下生物量为14.1 g/L,油脂含量为17.16%,微藻多糖含量为10.16%;而"异养-胁迫"分段培养模式下生物量13.20g/L,油脂含量40.15%,微藻多糖含量24.74%。本研究显示"异养-胁迫"分段培养模式是一种快速获得大量高油脂含量藻细胞的有效方法,可为规模化生产微藻生物柴油和进一步利用微藻奠定了技术基础。     

Denitrification on poly-beta-hydroxybutyrate in microbial granular sludge sequencing batch reactor

Microbial granules were successfully cultivated in an alternating aerobic-anaerobic sequencing batch reactor (SBR) for removing organic carbon and nitrogen. It was found that almost all input ammonium was converted to nitrite and nitrate in the aerobic phase, while the efficiency of denitrification was highly related to the availability of external carbon source in the anaerobic phase. Complete denitrification was achieved with sufficient supply of external carbon, while only partial denitrification was observed with no addition of external carbon. Results showed that in the absence of external carbon source, pre-accumulated poly-beta-hydroxybutyric acid (PHB) in microbial granules could be utilized for cell maintenance and denitrification. With supply of external carbon but no addition of nitrate, PHB accumulation accounted for the main mechanism of the organic removal. Under balanced growth conditions (with organic carbon and nitrogen supply), external organic carbon was consumed simultaneously for denitrification, PHB storage as well as for cell functions. It was revealed that the potential role of PHB for denitrification by microbial granules was very limited, i.e. less than 28 mg nitrate-nitrogen l(-1) was found to be denitrified with internally accumulated PHB. This study for the first time shows the limiting capacity of PHB as reducing power for denitrification by microbial granules.     

Effects of hydraulic and solids retention times on productivity and settleability of microbial (microalgal-bacterial) biomass grown on primary treated wastewater as a biofuel feedstock

High biomass productivity and efficient harvesting are currently recognized challenges in microbial biofuel applications. To produce naturally settleable biomass, combined growth of native microalgae and bacteria was facilitated in laboratory sequencing batch reactors (SBRs) using primary treated wastewater from the Christchurch Wastewater Treatment Plant (CWTP) in New Zealand. SBRs were operated under a simulated, local, summer climate (i.e., 925 μmol/m²/s of photosynthetically active radiation for 14.7 h per day at 21 °C mean water temperature) using 1.4- to 8-day hydraulic retention times (HRTs) to optimize growth. Solids retention times (SRTs) were varied from 4 to 40 days by discharging different ratios of supernatant and completely mixed culture. Biomass productivity up to 31 g/m²/day of solids was obtained, and it generally increased as retention times decreased. Biomass settleability was typically 70-95%, and the microbes aggregated into compact flocs as cultures aged up to four months. Due to a low lipid content of 10.5%, anaerobic digestion appeared to be the most appropriate biofuel conversion process with potential to generate 19,200 m³/ha/yr of methane based on settleable mixture productivity.     

Heterotrophic cultures of microalgae: metabolism and potential products

This review analyzes the current state of a specific niche of microalgae cultivation; heterotrophic growth in the dark supported by a carbon source replacing the traditional support of light energy. This unique ability of essentially photosynthetic microorganisms is shared by several species of microalgae. Where possible, heterotrophic growth overcomes major limitations of producing useful products from microalgae: dependency on light which significantly complicates the process, increase costs, and reduced production of potentially useful products. As a general role, and in most cases, heterotrophic cultivation is far cheaper, simpler to construct facilities, and easier than autotrophic cultivation to maintain on a large scale. This capacity allows expansion of useful applications from diverse species that is now very limited as a result of elevated costs of autotrophy; consequently, exploitation of microalgae is restricted to small volume of high-value products. Heterotrophic cultivation may allow large volume applications such as wastewater treatment combined, or separated, with production of biofuels. In this review, we present a general perspective of the field, describing the specific cellular metabolisms involved and the best-known examples from the literature and analyze the prospect of potential products from heterotrophic cultures.     

Is in-stream processing an important control on spatial changes in carbon fluxes in headwater catchments?

Data on small-scale spatial variations in instantaneous fluxes and concentrations of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and free carbon dioxide (CO2) are presented for a small acidic headwater stream in NE Scotland. Chloride is used as a conservative element to estimate additional, diffuse inputs of water into the main stem of the stream, other than those from tributaries. Downstream changes in instantaneous carbon fluxes were calculated and then used to estimate losses and gains of carbon within the stream system. Dissolved organic carbon concentrations in the stream ranged from 1.19-6.06 mg l(-1) at its source to a maximum of 10.0-25.3 mg l(-1) as the stream passed through deep peats; DOC concentrations then declined in the lower part of the catchment. DIC concentrations were initially low, increased to 1.5-3.0 mg l(-1) and then decreased to 0.1-1.65 mg l(-1) at the lowest site. Free CO2 concentrations increased from 0.35 mg l(-1) at the stream source to 3.30 mg l(-1) as the stream passed through the peat dominated area. Continually high inputs of CO2-rich water (> 6.0 mg l(-1)) from tributaries maintained these high concentrations in the main stem, until approximately 1.74 km downstream, when there was a rapid decline in concentration. Significant changes in DOC, DIC and CO2 fluxes occur over a distance of 2.7 km downstream from the stream source to the catchment outlet. Between 5.64-41.5 mg C s(-1) as DOC and 2.52-16.2 mg C s(-1) as DIC are removed from the water column. Between 6.81 and 19.0 mg C s(-1) as CO2 is lost along the stream length as progressive equilibration with the atmosphere occurs. We estimate that 11.6-17.6% of the total DOC flux is removed from streamwater by in-stream processes. Dissolved inorganic carbon (HCO3- and free CO2) losses are in excess of nine times its measured flux at the outlet of the catchment. These results suggest that in-stream processing of DOC and DIC and outgassing of CO2 are important controls on the spatial variability of carbon fluxes within headwater streams in upland catchments dominated by organic-rich soils.     

The ebullition of hydrogen, carbon monoxide, methane, carbon dioxide and total gaseous mercury from the Cornwall Area of Concern

This paper reports the first ebullitive fluxes of hydrogen (H2), carbon monoxide (CO), methane (CH4), carbon dioxide (CO2) and total gaseous mercury (TGM) from the Cornwall Area of Concern (CAC). Although sediments were contaminated with mercury, bubbling was a negligible source of mercury for the global atmosphere. Indeed, the average emission of TGM through ebullition was 0.04 pg m(-2) h(-1). Measurements of H2, CO, CH4 and CO2 trapped gas concentrations and fluxes were used as indicators of diagenesis processes. The CAC represented a significant regional source of CH4 since the estimated ebullitive fluxes (3.5 mg m(-2) h(-1)) were similar to the CH4 emissions measured above typical flooded freshwater wetlands. As molecular diffusion is known as the main pathway of CO2 transport from water to the atmosphere, CO2 ebullitive fluxes were weak (0.39 mg m(-2) h(-1)). Bubbling of CO (1.6 microg m(-2) h(-1)) was 10 folds less important than CO fluxes measured over flooded freshwater wetlands. Finally, H2 emissions (0.001 microg m(-2) h(-1)) were negligible since the level of this trace gas is tightly regulated by microorganisms in anaerobic environments.     

Towards a luxury uptake process via microalgae - Defining the polyphosphate dynamics

Microalgae in waste stabilization ponds (WSP) have been shown to accumulate polyphosphate. This luxury uptake of phosphorus is influenced by the wastewater phosphate concentration, light intensity and temperature, but the dynamics of how these factors affect luxury uptake with respect to time are not understood. With improved understanding of the dynamics of this mechanism and how it could be manipulated, a phosphorus removal process utilizing luxury uptake by microalgae might be developed. In this work, luxury uptake was investigated by chemical extraction of the acid-soluble and acid-insoluble fractions of polyphosphate in the microalgae. The results showed that the initial accumulation and subsequent utilization of both acid-soluble polyphosphate (ASP) and acid-insoluble polyphosphate (AISP) is a function of the wastewater phosphate concentration. It was found that light intensity influenced both the accumulation and utilization of ASP. The temperature influenced the accumulation of AISP. AISP is believed to be a form of phosphorus storage and ASP is involved in metabolism however, the results of this work show that ASP can also act as a short term form of phosphorus storage. To optimize luxury uptake by microalgae a ‘luxury uptake pond’ is proposed where the conditions the microalgae are exposed to can be manipulated. This ‘luxury uptake pond’ would be designed to expose the microalgae to a high phosphate concentration and high light intensity for a short period of time in order to achieve optimal polyphosphate accumulation. Subsequent harvesting would then remove the phosphorus rich microalgae from the system.     

Effect of lipids and oleic acid on biomass development in anaerobic fixed-bed reactors. Part I: Biofilm growth and activity

Two similar anaerobic fixed-bed bioreactors which allowed the biomass to be periodically withdrawn were run in parallel. After feeding each digester with synthetic dairy wastes of different lipid content (Period I), both digesters were fed with increasing sodium oleate concentrations with skim milk as co-substrate (Period II) and oleate as the sole carbon source (Period III). In Period I, the digester fed with lipids was more efficient and exhibited lower levels of volatile fatty acids than the digester fed without lipids. The biofilm built up in the presence of lipids was thinner, but more resistant to the presence of oleate than the biofilm formed in the absence of lipids, which lost 53% of its solids after contacting with oleic acid. The specific methanogenic activity with butyrate as substrate was enhanced in the presence of lipids, but no significant effect was detected on the acetoclastic and hydrogenophilic activities, which remained similar for both digesters along the trial period.     

Sludge characteristics in anaerobic SBR system producing hydrogen gas

In this study, sludge characteristics of anaerobic sequencing batch reactor (ASBR) were investigated to improve and optimize the efficiency of the system converting starch into biohydrogen. The effect of stratification in settling phase on H2-producing ASBR, which results in settleable and non-settleable sludge, was observed using a batch experiment. It was concluded that specific H2 activity of decanting non-settleable sludge was higher than that of settleable sludge, which may be the reason of low yield in H2-producing ASBR. In addition, effect of settling time on settleable sludge, which is another key operational parameter, was also analysed using another set of batch experiment. Settling time of the sludge was found to be an important parameter in H2-producing ASBR. Specific H2 activity varied inversely with the duration for which settleable microorganisms were contained in settling phase. Microbial species, responsible for H2 activity in each condition, were identified using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis.     

混合液及污泥回流比对MUCT工艺缺氧吸磷的影响

以C/N值较低的模拟生活污水为处理对象,研究了当硝化液回流比保持不变时,混合液回流比(r)和污泥回流比(s)对MUCT工艺缺氧吸磷的影响.结果表明:当r和s均为1时,缺氧区2和缺氧区3中的DPB利用厌氧段储存的大量PHB为碳源,以硝酸盐氮为电子受体进行吸磷,吸磷量分别稳定在132.91 mg/h和105.38 mg/h左右,缺氧吸磷率维持在46.58%左右;r和s对COD总去除率的影响不大,系统对COD、NH+4 -N、TP的去除率分别达到91.86%、98.83%和90%,出水COD、NH+4-N和11P分别在30、0.8和0.9 mg/L以下.