微藻在废水处理和生物质回收再利用方面的研究进展

随着经济的发展和人口的增加,环境污染和水资源短缺已经成为不可避免的全球性问题。基于微藻的废水处理技术不仅可以净化废水、解决环境污染问题,还可以利用废水中的营养元素合成生物质,现如今这种技术已经受到越来越多的关注。为了进一步提高废水处理效果、降低废水处理成本,有必要了解微藻去除废水中营养物质和污染物的机理,开发下游低成本收获技术,提升微藻高价值副产物的生产。本文综述了微藻去除碳、氮、磷、重金属、抗生素和有机物的机理和影响因素,总结了微藻的不同收获方式和微藻生物质在各个领域的应用。最后,分析了不同微藻共培养体系和微藻固定化技术的优缺点,并展望了微藻废水处理技术未来的发展方向。     

Growing Phototrophic Cells without Light

Many phototrophic microorganisms contain large quantities of high-value products such as n-3 polyunsaturated fatty acids and carotenoids but phototrophic growth is often slow due to light limitation. Some phototrophic microorganisms can also grow on cheap organic substrate heterotrophically. Heterotrophic cultivation can be well controlled and provides the possibility to achieve fast growth and high yield of valuable products on a large scale. Several strategies have been investigated for cultivation of phototrophic microorganisms without light. These include trophic conversion of obligate photoautotrophic microorganisms by genetic engineering, development of efficient cultivation systems and optimization of culture conditions. This paper reviews recent advances in heterotrophic cultivation of phototrophic cells with an emphasis on microalgae.     

Botryococcus braunii: A Renewable Source of Hydrocarbons and Other Chemicals

ABSTRACT:?

Botryococcus braunii, a green colonial microalga, is an unusually rich renewable source of hydrocarbons and other chemicals. Hydrocarbons can constitute up to 75% of the dry mass of B. braunii. This review details the various facets of biotechnology of B. braunii, including its microbiology and physiology; production of hydrocarbons and other compounds by the alga; methods of culture; downstream recovery and processing of algal hydrocarbons; and cloning of the algal genes into other microorganisms. B. braunii converts simple inorganic compounds and sunlight to potential hydrocarbon fuels and feedstocks for the chemical industry. Microorganisms such as B. braunii can, in the long run, reduce our dependence on fossil fuels and because of this B. braunii continues to attract much attention.     

A METHOD TO IMPROVE THE SPATIAL RESOLUTION OF PHOTOSYNTHETIC RATES OBTAINED BY OXYGEN MICROSENSORS

To determine gross photosynthesis in benthic microalgal communities, oxygen microelectrodes were used to measure the rate of decrease within the first 4 s after extinction of light. Photosynthetic rates calculated from third-order polynomial fits to the curve of decreasing O₂ concentration were compared to the rates obtained by the traditional method, where rates were estimated from linear regression. When photosynthesis was calculated for the fitted initial rates of O₂ decrease, maximum rates in microbial mats were up to 32% higher, and the depth-integrated gross photosynthesis was 5%–10% higher than the rates determined by the traditional method. The determinations from fitted initial rates also resulted in a more detailed profile of photosynthetic rate than that normally obtained. Computer simulation based on diffusion models, where the estimated initial rates of O₂ decrease were assumed to represent actual photosynthesis rates, verified the validity of the curve-fitting procedure for obtaining high-resolution photosynthesis profiles.     

Secretion of Free Fatty Acids by Prokaryotic and Eukaryotic Algae at Optimal,Supraoptimal, and Suboptimal Growth Temperatures

The paper describes the composition of extracellular free fatty acids (FFAs) and intracellular fatty acids (FAs) in the enrichment cultures of the prokaryotic alga Spirulina platensisand the eukaryotic alga Chlorella vulgarisgrown at optimal, supraoptimal, and suboptimal growth temperatures. With increasing growth temperature, the degree of unsaturation of the intracellular FAs of both algae decreased, while that of the extracellular FFAs of S. platensisincreased. The composition of the extracellular FFAs of C. vulgarispractically did not depend on the growth temperature.     

Selectivity and competitive interactions between two benthic invertebrate grazers (Asellus aquaticus and Potamopyrgus antipodarum): an experimental study using 13C- and 15N-labelled diatoms

1. Tracer experiments with two diatoms labelled with ¹³C (Nitzschia palea) and ¹⁵N (Fragilaria crotonensis), were conducted to investigate feeding selectivity and interspecific competition between the grazers Asellus aquaticus (Isopoda, Crustacea) and Potamopyrgus antipodarum (Hydrobiidae, Gastropoda). Conventional methods, such as cell counts and estimated biovolume, were used first to detect feeding preferences within the different grazer treatments. 2. The results revealed a significant decline in algal biovolume in all grazer treatments and no indications of active selectivity were observed. In contrast to conventional methods, measurements based on isotope signatures showed strong differences in tracer uptake, thus indicating different degrees of assimilation and digestion by the two grazers. 3. The selectivity index Q, which provides information on the uptake ratio of ¹³C to ¹⁵N, showed a significant time effect for both grazer species and a significant difference between single‐ and mixed‐grazer treatments for P. antipodarum. Thus, this technique enabled the direct quantification of the uptake by grazers and, therefore, served as an ideal tool for the detection of passive selectivity. 4. Our results indicate a shift in feeding preferences related to between‐species competition and a potential divergence of trophic niches when species coexist.     

Isolation of disproportionating enzyme from halotolerant microalga Dunaliella parva (Volvocales, Chlorophyceae)

Starch metabolism in Dunaliella parva Lerche is regulated by the osmolarity of the surrounding solute. Two isozymes showing amylolytic activity were obtained after purification by gel filtration chromatography. The isozymes show disproportionating activity (D‐enzyme) that is specific for malto‐oligosaccharides as substrate. Properties of the D‐enzyme in D. parva are similar to those in higher plants. The activity of the D‐enzyme is also found in various Dunaliella and Chlamydomonas, indicating that the D‐enzyme is also important in the starch metabolism in algae.     

Phycological expertise in geological applications

Our knowledge about fossil algae has been biased for a long time towards groups with calcified tissues such as dasyclads and crustose rhodophytes. This picture has recently begun to change owing to the growing number of discoveries of silicified microbial fossils and fossil microbial endoliths. There is good evidence that both groups contain a large proportion of photosynthetic organisms, particularly algae. Silicified microbial fossils are best known from the Precambrian strata, while microbial endoliths, which apparently evolved during middle to late Precambrian times are common throughout the Phanerozoic including the present. Because of the small size of these fossils, it is possible to study and morphometrically evaluate entire populations rather than individual specimens or body fragments. Thus, we are able to approach fossil taxa using largely biological rather than strictly paleontological criteria and to apply interpretations and reconstructions of biological species. Phycologists entering this field can contribute to the interpretation of such fossils by applying comparisons with modern algae, their life cycles, cellular organization, and cell division patterns. However, they have to learn to deal with post-mortem degradation and diagenetic changes, and to recognize algal remains from mineral features that surround and often obliterate the fossils. This work is often similar to that of a detective or coroner where the use of intuition and imagination is just as dangerous as it is necessary. Detection of microfossils between and within single carbonate grains in otherwise unfossiliferous rocks can provide valuable information for applied geology including petroleum exploration.     

The algal microflora of the salt works of Tarquinia (Italy)

The microflora and benthic microbial mats of the salt works of Tarquinia (Italy) are described. From 144 samples, 111 species and varieties of microalgae were identified. Diatoms prevailed up to 110. S. They were substituted by Cyanophyta at higher salinities. The microbial mats consisted of Cyanophyta, Beggiatoa spp., purple sulphur bacteria, and diatoms. Information on hypertonic resistance in some euryhaline species is given.     

Algal biotechnology products and processes — matching science and economics

Several microalgae, such as species ofChlorella, Spirulina andDunaliella, are grown commercially and algal products such as -carotene and phycocyanin are available. The main focus of algal biotechnology continues to be on high value fine chemicals and on algae for use as aquaculture feeds. This paper provides the outline for a rational approach in evaluating which algae and which algal products are the most likely to be commercially viable. This approach involves some simple market analysis followed by economic modelling of the whole production process. It also permits an evaluation of which steps in the production process have the greatest effect on the final production cost of the alga or algal product, thus providing a guide as to what area the research and development effort should be directed to. An example of this approach is presented and compared with other models. The base model used here gives a production cost of microalgal biomass at about AS 14 to 15 kg^–1, excluding the costs of further processing, packaging and marketing. The model also shows that some of the key factors in microalgal production are productivity, labor costs and harvesting costs. Given the existing technology, high value products such as carotenoids and algal biomass for aquaculture feeds have the greatest commercial potential in the short term.This paper was presented at the Symposium on Applied Phycology at the Fourth International Phycological Congress, Duke University.