Amos Richmond

EFFECT OF ENVIRONMENTAL CONDITIONS ON FATTY ACID COMPOSITION OF THE RED ALGA PORPHYRIDIUM CRUENTUM: CORRELATION TO GROWTH RATE

The lipid and fatty acid composition of Porphyridium cruentum was determined as a function of light intensity, temperature, pH, and salinity. In cultures cultivated at the optimal temperature under non‐limiting light conditions, eicosapentaenoic acid was the main polyunsaturated fatty acid. When growth rate was reduced by decreased light intensity, increased cell concentration, suboptimal temperature, suboptimal pH, or increased salinity, the content of eicosapentaenoic acid decreased and that of arachidonic acid increased, the latter becoming the major polyunsaturated fatty acid.

Production of spirulina biomass: Effects of environmental factors and population density

The effects of environmental conditions (solar irradiance and temperature) and population density on the production of Spirulina biomass are reported for cultures grown in outdoor ponds. Both the specific rate of photosynthesis, expressed on a chlorophyll basis, and the rate of respiration, on a protein basis, decreased as algal concentration increased. Higher specific growth rates were observed at lower population densities. Lower growth rates were associated with the light limitation in dense cultures for optimum conditions in the summer. Seasonal variation was observed in productivity. In summer light was the limiting factor whereas in winter the low daytime temperature appeared to impose the major limitation. It was found that the oxygen concentration in the culture can serve as a useful indicator of limiting factors and can also be used as a means of estimating the extent of such limitations.

Productivity and photosynthetic efficiency ofSpirulina platensis as affected by light intensity, algal density and rate of mixing in a flat plate photobioreactor

The effect of the rate of mixing on productivity of algal mass in relation to photon flux density and algal concentration was quantitatively evaluated in cultures ofSpirulina platensis grown in a newly designed flat-plate photobioreactor. Special emphasis was placed on elucidating the principles underlying efficient utilization of high photon flux density for maximal productivity of algal-mass. Whereas the rate of mixing exerted little influence on productivity and photosynthetic efficiency in cultures of relatively low algal density, its effect became ever more significant as algal concentration was increased. Maximal mixing-enhanced cell concentrations and productivity of biomass were obtained at the highest light intensity used. At each level of incident light intensity, maximum productivity and photosynthetic efficiency could be achieved only when algal concentration and mixing rates were optimized. The higher the intensity of the light source, the higher became the optimal culture density, highest algal concentrations and productivity of biomass being obtained at the highest light intensity used. The rate of mixing required careful optimization: when too low, maximal productivity resulting from the most efficient utilization of light could not be obtained. Too high a rate of mixing resulted in cell damage and reduced output rate.

Isolation and characterization of phycocyanins from the blue-green alga Spirulina platensis

Two main biliproteins c-phycocyanin and allophycocyanin were identified and characterized in the blue-green alga Spirulina platensis. The specific absorbance, fluorescence maxima, sub-unit make-up and amino acid composition of the biliproteins in Spirulina platensis resemble those reported for other blue-green algae. However, the minimum molecular weights (44,000 for c-phycocyanin and 38,000 for the allophycocyanin) and the specific extinction coefficients (73, and 58 for c-phycocyanin and allophycocyanin respectively) of these biliproteins were different from these values in other blue-green algae.

A new tubular reactor for mass production of microalgae outdoors

A novel reactor for outdoor production of microalgae is described. Air-lift is used for circulation of the culture in transparent tubes lying on the ground and interconnected by a manifold. Dissolved O2 is removed through a gas-separator placed 2.0 m above the tubes and water-spray is used for cooling. The manifold permits short-run durations between leaving the gas separator and re-entering it, preventing thereby damaging accumulation of dissolved oxygen. Day temperature control in summer is attained using water-spray. In winter, temperature in the tubes rises rapidly in the morning, as compared to an open raceway even if placed in a greenhouse. The number of hours along which optimal temperature prevails in the culture throughout the year increased significantly. Very high daily productivity computed on a volumetric basis (e.g. 550 mg dry wt l−1 culture) was obtained and preliminary observations indicate that a significantly higher output, e.g. 1500 mg dry wt l−1 d−1 is attainable. Much more research is required to assess the year-round, sustained productivity attainable in this reactor.

Microalgal biotechnology at the turn of the millennium: A personal view

I was grateful – and indeed honored – to have had the opportunity to provide the opening presentation for the 1999 International Conference on Applied Algology based on my personal views. Microalgal biotechnology at the end of the millennium – and after some fifty years of much research, requires some ‘soulsearching’, for I cannot help a feeling of disappointment over the fact that Microalgal Biotechnology after so many years is still in its infancy, a sort of esoteric endeavor with a ‘great future’, which somehow does not get off the ground. One reason for the disappointment in the progress made in mass cultures is rooted in the reasons why I was originally so enthusiastically attracted to microalgaculture close to 30 years ago, in the early 1970s. The prospect of a novel method by to save the hungry and poor part of humanity excited me: Here was a worthwhile goal in life, a fantastic scientific challenge. After reading the works done in the early 1950s (Burlew, 1953), I adopted what I perceived as the ‘Microalgae Doctrine’ according to which microalgalculture, in suitable geographic regions, can augment and even replace, cost effectively, conventional agricultural productivity. In spite of the many good reasons given for the superiority of algae over horticultural crops, by the early 1980s, it became very clear that mass production of microalgae as an agricultural commodity, providing e.g. protein, starch or oil, was a distant dream, not to be reached in the foreseeable future. Indeed, the false alarm of an impending food crisis, forecast by the United Nations Advisory Committee (Anonymous, 1967), which predicted an acute shortage of protein by the year 2000, only adds insult to injury. Hence the sober view held by some that microalgal biotechnology has a limited future, confined to specialized, relatively expensive products, which naturally have a rather limited market. Personally, I still believe that in the long run, phototrophic microorganisms will play a role similar to that which heterotrophic microorganisms have today. The basic idea of using solar energy to produce photoautotrophic or mixotrophic cell mass for food, feed and industrial chemicals, particularly on marginal agricultural resources such as sea water along coastal dry lands, is as valid as ever. It is nevertheless obvious that the coming of age of microalgal biotechnology has proved a very slow process. What is holding this technology back?

Combined effects of light intensity, light-path and culture density on output rate of Spirulina platensis (Cyanobacteria)

The requirements for efficient utilization of high light fluxes in cultures of Spirulina platensis have previously been elucidated. The most important of these was a short light-path coupled with a highly turbulent flow, facilitating ultrahigh cell densities (i.e. above 100 mg chl l−1). The present study shows that for each irradiance there is an optimal culture density, defined as the concentration that yields the highest output rate of cell mass under the prevailing conditions. In ultrahigh cell density cultures, a linear relationship was observed between the output rate and the irradiance, up to a photon flux density (PFD) of 2500 μmol m−2 s−1. Using a total PFD of 8000 μmol m−2 s−1, a maximal output rate of 16.8 g dry weight m−2 h−1 was obtained, which is the highest reported for a culture of photoautotrophic microorganisms exposed to direct beam radiation. Testing the effect of reduction in light-path on productivity, output rate per unit volume increased 50-fold as the light-path was reduced 27-fold...

Principles for attaining maximal microalgal productivity in photobioreactors: an overview

Efficient management of mass algal cultures requires appreciation of the most important factors governing the light regime of the average cell, i.e. the interrelationships between the intensity of the light source — never the sole factor involved in mass culture productivity — and the optimal cell density affected by the optical path. The latter is a dominant factor in photosynthetic productivity of ultra high cell density cultures (UHDC) cultured in flat plate reactors. Indeed, a very short optical path (5–10 mm) permits a most efficient use of strong light by facilitating ultra-high cell densities (ca. 10–20 g dry cell mass 1−1), in which the condensed cells are exposed to very high frequency light/dark cycles. Another important feature of dense cultures concerns the very small but highly efficient light dose available to cells under extreme mutual shading. The low productivity of the single cell in the culture is well compensated, in terms of culture productivity, by the high culture cell mass exposed to very high frequency light/dark cycles. The combined effects of all these factors result in high efficiency of strong light-use for photosynthesis. UHDC are associated with growth inhibition which represents a severe production obstacle. Once this aspect is better understood and managed, UHDC in ultra short optical path reactors may become a useful production mode of photoautotrophic cell mass and secondary metabolites.

Optimization of a flat plate glass reactor for mass production of Nannochloropsis sp. outdoors

The relationships between areal (g m(-2) per day) and volumetric (g l(-1) per day) productivity of Nannochloropsis sp. as affected by the light-path (ranging from 1.3 to 17.0 cm) of a vertical flat plate glass photobioreactor were elucidated. In general, the shorter the length of the light-path (LP), the smaller the areal volume and the higher the volumetric productivity. The areal productivity in relation to the light-path, in contrast, yielded an optimum curve, the highest areal productivity was obtained in a 10 cm LP reactor, which is regarded, therefore, optimal for mass production of Nannochloropsis. An attempt was made to identify criteria by which to assess the efficiency of a photobioreactor in utilizing strong incident energy. Two basic factors which relate to reactor efficiency and its cost-effectiveness have been defined as (a) the total illuminated surface required to produce a set quantity of product and (b) culture volume required to produce that quantity. As a general guide line, the lower these values are, the more efficient and cost-effective the reactor would be. An interesting feature of this analysis rests with the fact that an open raceways is as effective in productivity per illuminated area as a flat-plate reactor with an optimal light path, both cultivation systems requiring ca. 85 m(2) of illuminated surface to produce 1 kg dry cell mass of Nannochloropsis sp. per day. The difference in light utilization efficiency between the two very different production systems involves three aspects - first, the open raceway requires ca. 6 times greater volume than the 10 cm flat plate reactor to produce the same quantity of cell-mass. Second, the total ground area (i.e. including the ground area between reactors) for the vertical flat plate reactor is less than one half of that occupied by an open raceway, indicating the former is more efficient, photosynthetically, compared with the latter. Finally, the harvested cell density is close to one order of magnitude higher in the flat plate reactor, which carries economic significance. The advantage of vertical lamination of photoautotrophic cells provided by vertical plate reactors, is thereby clearly seen. The optimal population density (i.e. which results in the highest areal productivity) in the 10 cm plate reactor was obtained by a daily harvest of 10% of culture volume, yielding an annual average of ca. 12.1 g dry wt. m(-2) per day (on the basis of the overall illuminated reactor surfaces, i.e. front and back) or 240 mg l(-1) per day.

Lipid and biomass production by the halotolerant microalga Nannochloropsis salina

The effect of environmental factors on cell-lipid content, on the growth rate and on the overall productivity of Nannochloropsis salina was tested in the laboratory and in outdoor cultures. Under optimum conditions in the laboratory, the maximum growth rate (μmax) was 0·030 h−1, which corresponds to a doubling time of 23 h. Cellular lipid content was affected by the phase of growth and the temperature, but not by nitrogen starvation, pH or the source of sea water. The most important factor affecting the output rate of biomass was the cell concentration. The maximum biomass productivity obtained in outdoor ponds was 24·5 g·m−2·day−1, and the lipid production rate was 4·0 g m−2·day−1.