微藻采收技术的研究进展

微藻作为一种有巨大应用前景的生物质资源,在环境保护、废水处理和清洁能源等领域广泛应用。但是微藻采收成本过高严重限制了微藻产业的发展,因此,寻找一种经济、环保、高效的采收技术对促进微藻产业的发展具有十分重要的意义。本文分析了常用微藻采收技术的优缺点,包括离心分离、沉降、过滤、浮选和絮凝技术,重点论述絮凝技术在微藻采收方面的研究进展,以期为微藻高效、低成本采收方案的选择及其研究方向提供参考。     

Cultivation, photobioreactor design and harvesting of microalgae for biodiesel production: A critical review

Microalgae have the ability to mitigate CO₂ emission and produce oil with a high productivity, thereby having the potential for applications in producing the third-generation of biofuels. The key technologies for producing microalgal biofuels include identification of preferable culture conditions for high oil productivity, development of effective and economical microalgae cultivation systems, as well as separation and harvesting of microalgal biomass and oil. This review presents recent advances in microalgal cultivation, photobioreactor design, and harvesting technologies with a focus on microalgal oil (mainly triglycerides) production. The effects of different microalgal metabolisms (i.e., phototrophic, heterotrophic, mixotrophic, and photoheterotrophic growth), cultivation systems (emphasizing the effect of light sources), and biomass harvesting methods (chemical/physical methods) on microalgal biomass and oil production are compared and critically discussed. This review aims to provide useful information to help future development of efficient and commercially viable technology for microalgae-based biodiesel production.     

The impact of cell wall carbohydrate composition on the chitosan flocculation of Chlorella

The carbohydrate composition of the algal cell wall was investigated for its role in cell flocculation. Cultures of Chlorella variabilis NC64A, which were found to have different levels of neutral sugar, uronic acid and amino sugar in the cell wall when cultured in different nitrogen sources and concentrations, were subjected to flocculation with chitosan at dosages of 0–69.6 mg/l and pH values of 5.5, 7 and 8.5. In addition, flocculations of another three strains of Chlorella, which have different levels of cell wall components, were tested. Flocculation improved for all strains at pH 8.5 suggesting that inter molecular forces such as hydrogen bonding might be more important than charge neutralization in the flocculation of Chlorella. Total carbohydrate content in the cell wall was the most significant factor positively affecting the flocculation efficiency of C. variabilis NC64A cells with different cell wall compositions and the other Chlorella strains. The results presented in this study suggest that chitosan flocculation can be improved by optimizing the cell culture conditions to achieve higher cell wall polysaccharide content or selecting an algal strain with higher cell wall polysaccharide content.     

Silver/chitosan nanocomposites induce physiological and histological changes in freshwater bivalve

BackgroundBivalves can accumulate and concentrate most pollutants, even if they are present in somewhat low concentrations. The present study aimed to use freshwater bivalveas for the first time as vital indicator for silver/chitosan nanocomposites (Ag-CS NCs) in the freshwater environment.MethodsFollowing the preparation and characterization of Ag-CS NCs by using UV–vis spectrophotometer, X-ray diffraction, transmission electron microscopy, and acute toxicity study, the animals exposed to three different dose of nano chitosan (CS), AgNPs, and Ag-CS NCs (12.5, 25 and 50 mg/L) for consecutive 6 days.ResultsAg-CS particles were in size range of 8–19 nm. The nominal concentrations for Ag-CS NCs were 12.5, 25 and 50 mg Ag L⁻¹ were corresponding to measured concentration of AgNPs 0.37, 0.81, and 1.65 mg Ag L⁻¹, respectively. All concentrations of Ag-CS NCs caused a significant increase in MDA and NO, while GSH and CAT levels decreased significantly in all organs. Histological investigation of the gills, labial palp and foot tissues showed alternation after exposure to Ag-CS NCs, especially at dose 50 mg/L.ConclusionThe present study showed that exposure to Ag-CS NCs caused oxidative stress responses in Coelatura aegyptiaca and histological changes in the organs. These physiological and histological changes observed after exposure to Ag-CS NCs were most likely the result of the action of AgNPs themselves while the effect of chitosan on these changes was negligible. We concluded that Coelatura aegyptiaca was a sensitive bio-indicator for monitoring of the past and the present water pollution by nanoparticles.     

Flocculation of algae using chitosan

Flocculation of three freshwater algae, Spirulina,Oscillatoria and Chlorella, and onebrackish alga, Synechocystis, using chitosan was studiedinthe pH range 4 to 9, and chlorophyll-a concentrations inthe range 80 to 800 mg m^–3, which produces aturbidity of 10 to 100 nephelometric turbidity units (NTU) in water. Chitosanreduced the algal content effectively by flocculation and settling. Theflocculation efficiency is very sensitive to pH, and reached a maximum at pH7.0for the freshwater species, but lower for the marine species. The optimalchitosan concentration that is required to effect maximum flocculation dependedon the concentration of alga. Flocculation and settling were faster whenconcentrations of chitosan higher than optimal are used. The settled algalcellsare intact and live, but will not be redispersed by mechanical agitation. Thede-algated water may be reused to produce fresh cultures of algae.     

Optimal harvesting of an age-structured population

Here we investigate the optimal harvesting of an age-structured population. We use the McKendrick model of population dynamics, and optimize a discounted yield on an infinite time horizon. The harvesting function is allowed to depend arbitrarily on age and time and its magnitude is unconstrained. We obtain, in addition to existence, the qualitative result that an optimal harvesting policy consists of harvesting at no more than three distinct ages.     

Evaluation of electro‐coagulation–flocculation for harvesting marine and freshwater microalgae

Although microalgae are considered as a promising feedstock for biofuels, the energy efficiency of the production process needs to be significantly improved. Due to their small size and low concentration in the culture medium, cost‐efficient harvesting of microalgae is a major challenge. In this study, the use of electro‐coagulation–flocculation (ECF) as a method for harvesting a freshwater (Chlorella vulgaris) and a marine (Phaeodactylum tricornutum) microalgal species is evaluated. ECF was shown to be more efficient using an aluminum anode than using an iron anode. Furthermore, it could be concluded that the efficiency of the ECF process can be substantially improved by reducing the initial pH and by increasing the turbulence in the microalgal suspension. Although higher current densities resulted in a more rapid flocculation of the microalgal suspension, power consumption, expressed per kg of microalgae harvested, and release of aluminum were lower when a lower current density was used. The aluminum content of the harvested microalgal biomass was less than 1% while the aluminum concentration in the process water was below 2 mg L⁻¹. Under optimal conditions, power consumption of the ECF process was around 2 kWh kg⁻¹ of microalgal biomass harvested for Chlorella vulgaris and ca. 0.3 kWh kg⁻¹ for Phaeodactylum tricornutum. Compared to centrifugation, ECF is thus more energy efficient. Because of the lower power consumption of ECF in seawater, ECF is a particularly attractive method for harvesting marine microalgae. Biotechnol. Bioeng. 2011;108: 2320–2329. © 2011 Wiley Periodicals, Inc.     

Linear age-dependent population growth with seasonal harvesting

A population growth is modelled by the Von Foerster PDE with accompanying Lotka-Volterra integral equation describing the birth rate; the age specific death and fertility rates are assumed to depend only on age and not time. A harvesting policy where a fraction of the population of age greater than a given age is harvested for a fraction of a given season. This introduces a time dependence, but this difficulty is circumvented by devising approximate timeindependent models whose birthrates bracket the true birthrate-the standard renewal equation theory applies to the approximate models so quantitative results can be obtained.The author wishes to thank Professors J. J. Levin and R. K. Miller for some useful remarks. This research was partially supported by NIH Grant GMO 7661-02.     

Preparation of low molecular weight chitosan using solution plasma system

The solution plasma system was introduced to treat chitosan solution in order to prepare low molecular weight chitosan. The plasma treatment time was varied from 0 min to 300 min. The plasma-treated chitosan was characterized including viscosity, molecular weight by GPC, and chemical characteristics by FT-IR. The results showed that after treated with plasma for 15-60 min, the viscosity of chitosan solution and apparent molecular weight of chitosans were remarkably decreased, compared to those of untreated sample. Longer treatment time had less effect on both viscosity and molecular weight of samples. Eventually, long treatment time (≥180 min) showed no influence on both viscosity and apparent molecular weight. This suggested that the degradation process of chitosan occurred during plasma treatment. FT-IR analysis revealed that chemical structure of chitosan was not affected by solution plasma treatment. TOF-MS results showed that chitooligosaccharides with the degree of polymerization of 2-8 were also generated by solution plasma treatment. The results suggested that solution plasma system could be a potential method for the preparation of low molecular weight chitosan and chitooligosaccharides.     

微藻采收方法的研究进展

微藻的生产过程可以实现能源生产、废水净化和CO2减排的高度耦合,在能源危机日益紧张、环境问题日趋严峻的今天,微藻的开发利用具有重要的研究价值和经济、社会效益。制约微藻产业化的瓶颈问题是采收成本过高,一种经济合理的采收方法不但可以大大降低生产成本,还可以奠定微藻产业化发展的基础。本文对目前应用较为普遍的微藻采收方法进行了介绍,重点阐述了絮凝法采收微藻,以期对微藻的低成本高效率采收以及产业化发展提供帮助。     

A study of the distribution of chitosan onto and within a paper sheet using a fluorescent chitosan derivative

Acidic glutaraldehyde (Gh) crosslinked chitosan (ChGhH) when deprotonated the biopolymer (ChGh) presents high content of free amino groups. These modified biopolymers are comparable to epichlorohydrin (Ep) crosslinked (ChEp). C/N molar ratio of 6.1 for chitosan increases to 7.3, 7.5 and 7.1 for ChGhH, ChGh and ChEp. The effectiveness of the carbon-6 hydroxyl group in interconnecting chitosan units was supported by IR and ¹³CNMR, where Ep promotes increase in crystallinity. Copper uptake gave the order Ch > ChGh > ChGhH > ChEp, as: 1.35 ± 0.06, 1.30 ± 0.05, 1.05 ± 0.07 and 0.96 ± 0.22 mmol g⁻¹, reflecting the availability of nitrogen basic centers in adsorbing. The favorable thermodynamic data of adsorption through calorimetric titration gave exothermic enthalpic values: −28.98 ± 0.05, −6.68 ± 0.04, −6.13 ± 0.07 and −0.65 ± 0.23 kJ mol⁻¹ for Ch, ChGh, ChGhH and ChEp. Free Gibbs energy reflected spontaneity of interactions and, with the exception of chitosan, the entropic values are positive.     

The selection of a surfactant for freshwater microalgae harvesting and separation by the foam separation method

Bioprocess and Biosystems Engineering - Collecting microalgae from water with less energy and cost is significant to gain economic profit from microalgae harvesting and processing. Foam separation...     

Recovery of microalgal biomass and metabolites: process options and economics

Commercial production of intracellular microalgal metabolites requires the following: (1) large-scale monoseptic production of the appropriate microalgal biomass; (2) recovery of the biomass from a relatively dilute broth; (3) extraction of the metabolite from the biomass; and (4) purification of the crude extract. This review examines the options available for recovery of the biomass and the intracellular metabolites from the biomass. Economics of monoseptic production of microalgae in photobioreactors and the downstream recovery of metabolites are discussed using eicosapentaenoic acid (EPA) recovery as a representative case study.     

Polyelectrolyte complex formation using alginate and chitosan

Polyelectrolyte complexes (PECs) of alginate and chitosan were formed by addition of 0.1% alginate solution (pH 6.5) to 0.1% chitosan solution (pH 4.0), and by adding the chitosan solution to the alginate solution under high shearing conditions. Variations in the properties of the polymers and the preparation procedure were studied, and the resultant PEC size, zeta potential (Zp), and pH were determined using dynamic light scattering (DLS), electrophoresis and by measuring turbidity and pH. Tapping mode atomic force microscopy (AFM) was used to examine some of the complexes. The particle size was decreased as the speed and diameter of the dispersing element of the homogenizer was increased. The net charge ratio between chitosan and alginate, and the molecular weights (M_W) of both the alginate and chitosan samples were the most significant parameters that influenced the particle size, Zp, and pH. The mixing order also influenced the size of the PECs, however, the Zp and pH were not affected by the mixing order. The stability of the complexes was investigated by incubation at an elevated temperature (37 °C), storage for one month at 4 °C, alteration of the pH of the PEC mixture, and addition of salt to physiological ionic strength (0.15 M NaCl). The properties of the PEC could be affected according to the molecular properties of the polyelectrolytes selected and the preparation procedures used. The resultant PEC sizes and properties of the complex were rationalised using a core-shell model for the structure of the complexes.     

植被砍伐对土壤养分的影响

研究了不同砍伐频率下,香港、深圳和鹤山研究样地山坡地Ｎ、Ｐ、Ｋ含量的差异．不同采样地之间,养分全量和有效量差异显著．在尚未砍伐的山坡地,土壤养分含量显著高于经常砍伐的山坡地．未伐土壤的Ｎ含量顺序为香港样地＞深圳样地＞鹤山样地．下层土壤Ｐ的含量高于上层土壤．深圳样地常代土壤养分含量高于鹤山．结果建议采用最适砍伐频率和在最适季节砍伐,以便减少砍伐产生的不利影响．     

The preparation of low-molecular-weight chitosan using chitinolytic complex from Streptomyces kurssanovii

Streptomyces kurssanovii are Gram-positive mycelial bacteria ubiquitous in soil. They have a saprophytic way of life and produce many extracellular enzymes with polymer-degrading properties, for example, chitinase (EC 3.2.1.14) and N-acetyl-β- -glucosaminidase (EC3.2.1.30). Biochemical aspects of chitosan degradation were presented. Low-molecular-weight (LMW) chitosans with molecular weight 4–8 kDa were prepared from commercial crab chitosan by means of chitinolytic a complex from S. kurssanovii. The optimum conditions of process in solution (temperature, pH, enzyme-substrate ratio) have been determined. Yields of LMW chitosan were 70–80%.     

絮凝微生物采收微藻的作用机制研究进展

微藻广泛分布于自然界,其易培养,生长快且应用价值高,普遍用于生物燃料、医学原料、优质食品源及畜牧养殖业等。近年来,通过对光生物反应器改造设计、高产藻株筛选、代谢通路基因改造等方法实现微藻产量的提高,而在微藻处理的下游过程的研究与创新不足,特别是微藻采收已经成为其产业发展的瓶颈。本文综述了絮凝法在微藻采收中的作用,重点讨论了絮凝微生物在微藻采收中的作用,并对絮凝微生物对微藻的絮凝机制进行广泛探讨,为絮凝微生物采收微藻提供理论依据。     

Coagulation/flocculation-based removal of algal-bacterial biomass from piggery wastewater treatment

Two conventional chemical coagulants (FeCl₃ and Fe₂(SO₄)₃) and five commercial polymeric flocculants (Drewfloc 447, Flocudex CS/5000, Flocusol CM/78, Chemifloc CV/300 and Chitosan) were comparatively evaluated for their ability to remove algal-bacterial biomass from the effluent of a photosynthetically oxygenated piggery wastewater biodegradation process. Chlorella sorokiniana, Scenedesmus obliquus, Chlorococcum sp. and a wild type Chlorella, in symbiosis with a bacterial consortium, were used as model algal-bacterial consortia. While the highest biomass removals (66-98%) for the ferric salts were achieved at concentrations of 150-250 mg L⁻¹, dosages of 25-50 mg L⁻¹ were required for the polymer flocculants to support comparable removal efficiencies. Process efficiency declined when the polymer flocculant was overdosed. Biomass concentration did not show a significant impact on flocculation within the concentration range tested. The high flocculant requirements herein recorded might be due to the competition of colloidal organic for the flocculants and the stationary phase conditions of biomass.