It is used not only as an additive in pharmaceutical and cosmetic products but also as a natural food colouring agent. Additionally, it has antioxidant and antimutagenic properties. This review discusses the process engineering of chlorophyll extraction from microalgae. Different chlorophyll extraction methods and chlorophyll purification techniques are evaluated. Our preliminary analysis suggests supercritical fluid extraction to be superior to organic solvent extraction.
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Michael Borowitzka Journal of Biotechnology 70 — Commercial production of microalgae: ponds, tanks, tubes and fermenters Michael A. The culture systems currently used to grow these algae are generally fairly unsophisticated.
For example, Dunaliella salina is cultured in large up to approx. Similarly, Chlorella and Spirulina also are grown outdoors in either paddle-wheel mixed ponds or circular ponds with a rotating mixing arm of up to about 1 ha in area per pond. The production of microalgae for aquaculture is generally on a much smaller scale, and in many cases is carried out indoors in 20 — 40 l carboys or in large plastic bags of up to approximately l in volume.
Other closed photobioreactors such as flat panels are also being developed. The main problem facing the commercialisation of new microalgae and microalgal products is the need for closed culture systems and the fact that these are very capital intensive.
The high cost of microalgal culture systems relates to the need for light and the relatively slow growth rate of the algae. Although this problem has been avoided in some instances by growing the algae heterotrophically, not all algae or algal products can be produced this way.
All rights reserved. Keywords: Photobioreactors; Chlorella; Spirulina; Dunaliella 1. Introduction garis, and the use of such cultures for studying plant physiology was developed by Warburg in Microalgal culture is one of the modern bio- the early s Warburg, Mass culture of technologies. E-mail address: borowitz possum. However, aside from the specialised Becker, ; Wharton et al. Other lowed in the early s with the establishment of commercial large-scale systems include tanks used a Spirulina harvesting and culturing facility in in aquaculture, the cascade system developed in Lake Texcoco, Mexico by Sosa Texcoco S.
Table 1 Chlorella per month Kawaguchi, and in summarises the culture systems currently in use about t of Chlorella were traded in for commercial algal culture. Japan alone Lee, Commercial production of Dunaliella salina as a source of b-carotene became the third major microalgae industry when production facilities were established by Western Biotechnology Ltd and Betatene Ltd in Australia in These were soon followed by other com- mercial plants in Israel and the USA.
As well as these algae, the large-scale production of cyanobacteria blue — green algae commenced in India at about the same time Venkatamaran, Thus in a short period of about 30 years the industry of microalgal biotechnology has grown and diversified significantly. The growth of commercial microalgae production is probably best illustrated by data on Spirulina production for which reasonably reliable figures are available Fig. The success of commercial large-scale produc- tion of microalgae depends on many factors, and one of these is the development of cost effective large-scale culture systems for the algae and the development of these has been, and continues to be, a gradual process.
This paper will review some of the steps along the way and the future ad- vances we can expect. Global production figures of Spirulina by country 2. Culture systems based on literature, company and trade information.
Figures for and are estimates based on projected production Existing commercial microalgae culture systems figures provided by the producers. USA closed reactor and then out- doors in paddlewheel ponds a These are order of magnitude estimates only. There are several considerations as to which Those species of algae which do not have this culture system to use. Factors to be considered selective advantage must be grown in closed sys- include: the biology of the alga, the cost of land, tems.
This includes most of the marine algae labour, energy, water, nutrients, climate if the grown as aquaculture feeds e. Skeletonema, culture is outdoors and the type of final product Chaetoceros, Thalassiosira, Tetraselmis and Borowitzka, The various large-scale cul- Isochrysis and the dinoflagellate C.
Open-air systems how easy they are to scale up from laboratory scale to large-scale. These properties are com- Although much of the early work on microalgal pared in Table 2. The final choice of system is mass culture focused on closed culture systems almost always a compromise between all of these see Burlew, all very large commercial sys- considerations to achieve an economically accept- tems used today are open-air systems Table 1.
The reason for this is simple economics; closed A common feature of most of the algal species culture systems are very expensive and many of currently produced commercially i. Chlorella, them are difficult to scale up. Furthermore, most Spirulina and Dunaliella is that they grow in closed systems are operated indoors with artificial highly selective environments which means that lighting and this results in high energy costs they can be grown in open air cultures and still whereas open air systems can utilise sunlight.
Thus, Chlorella grows well in can be grown successfully in open air systems. This means that productivities have to be ties of the alga as well as local climatic conditions maximised to offset the high capital costs of the and the costs of land and water.
For example, the ponds and associated production systems such as Australian producer of D. The pond depth is a compromise and the climate is close to optimum so that pro- between the need to provide adequate light to the duction can be achieved all year round.
Further- algal cells i. On adequate water depth for mixing and to avoid the other hand, the other Dunaliella producers in large changes in ionic composition due to evapo- the USA no longer in operation and in Israel use ration. Thus most paddle-wheel raceway ponds paddle-wheel driven raceway ponds to achieve are between 20 and 30 cm deep and the very large higher cell densities Ben-Amotz, This is up to approx. This means that, in almost all cases, the algae are light limited and the maxi- significant.
As well as this they require the addi- mum biomass achieved on a regular basis is be- tion of NaCl to the medium which is a significant tween approx. These factors mean that pond and productivity has been most extensively stud- area and volume must be minimised and the cell ied for Spirulina cf.
Vonshak, and is impor- density in the culture must be maximised in order tant for maximising the biomass output. The to have an economical process. The linity Belay, In this system the culture ha within Lake Texcoco where Spirulina grows depth is less than 1 cm and cell densities up to naturally. The Trebon system is very expensive with Mexico City. However, improved materials mean that a means that Spirulina and Chlorella must be grown similar system could now be constructed at signifi- in batch or semi-batch mode with periodical re- cantly lower cost Doucha, personal communica- seeding of ponds with new inoculum Kawaguchi, tion.
Furthermore the central European location ; Belay, Furthermore, many of these of Trebon means that there is a relatively short algal plants are located in regions with climatic annual culture period. Preliminary calculations conditions which do not allow year round produc- indicate that this system would be very competi- M. A similar system Parker, ; Running et al.
However, comprising a 0. The main disad- was used to produce Chlorella near Dongara, vantages are that heterotrophic cultivation is not Western Australia, for several years. Unfortunately technical problems with widely used in the aquaculture industry for the further scale-up eventually led to the closure of production of a range of algal species.
The most this plant. These systems use large sterile 4. Closed systems plastic bags of about 0. Although most of these sys- Despite the success of open systems, future tems are operated in batch mode, semi-continuous advances in microalgal mass culture will require systems have also been developed.
A variant on closed systems as the algal species on interest do this system has been developed by Cohen and not grow in highly selective environments. Fur- Arad using multiples of narrower bags; thermore, many of the new algae and algal prod- however there appears to be no commercial pro- ucts must be grown free of potential contaminants duction as yet using this system.
The oper- Algae can be grown in closed systems either pho- ation of these systems is also labour intensive and toautotrophically, mixotrophically or hetero- the cultures are generally inadequately mixed, trophically. This makes Heterotrophic cultivation on acetate or glucose the algae expensive to produce. More recently, Tanticharoen et al. Heterotrophic culture tems are likely to be commercial realities in the has several advantages: i fermentation systems near future.
The two basic designs are the flat are well understood and there is wide experience plate reactors Pulz, ; Hu et al. The fun- diaphragm or lobe pumps, the type of pump used damental principle in all of these designs is to depends on the species of alga grown.
If required reduce the light path and thus to increase the a gas exchange tower may also be incorporated in amount of light available to each cell. These the circuit. Temperature control is either by a heat reactors are also well mixed to ensure optimum exchanger or by evaporative cooling by flowing light availability to the cells and to enhance gas water over the photostage surface. We have exchange.
The optimum thickness of the algal grown a wide range of marine microalgae includ- culture in these reactors is between 2 and 4 cm. The the production of Spirulina and another l design of the BIOCOIL ensures uniform mixing unit in Elbingerode, Germany is growing and minimises adhesion of the algal cells to the Chlorella using waste CO2 from a lime factory inside of the tubes. Depending on need, the sys- efficiency leading to high productivities as high tem can be designed to be operated as an axenic sustainable biomass, temperature control and the culture.
Not all algal species are suitable for culture in This means that a much wider range of species this system. There is However, systems such as the BIOCOIL greatly also a greater ability to control the culture condi- expand the suite of algae which can be grown on tions so that the final product is of more consis- tent composition and quality e.
Chrismadha a large scale and provide the opportunity to de- and Borowitzka, Finally, these systems are velop new algae and algal products such as bioac- amenable to operation in continuous culture tive molecules Borowitzka, They will also mode. Continuous culture and good control over serve to reduce the costs associated with the pro- the growth environment results in a consistent duction of algae such as those species used in product quality and the higher operating cell den- aquaculture.
The challenge now is to reduce the construction costs 5. Conclusions of these systems further to make them more eco- nomically competitive. Most of the culture systems in use design at present Robinson et al. Robinson and Morrison, The BIOCOIL is However, over the last 50 years great advances a helical tubular photobioreactor consisting of a have been made in our understanding of the photostage of small diameter clear plastic tubing biology of the algae and in the engineering re- between 2.
Several parallel bands of tubes are con- of closed photobioreactors which will enable the nected via manifolds to a pumping system which commercialisation of new algae and algal prod- may be an airlift or pumps such as centrifugal, ucts in the next decade. Production and use of Spirulina in Mexico. In: Shelef, G. Arthur D. Little Inc.
Michael Borowitzka Journal of Biotechnology 70 — Commercial production of microalgae: ponds, tanks, tubes and fermenters Michael A. The culture systems currently used to grow these algae are generally fairly unsophisticated. For example, Dunaliella salina is cultured in large up to approx. Similarly, Chlorella and Spirulina also are grown outdoors in either paddle-wheel mixed ponds or circular ponds with a rotating mixing arm of up to about 1 ha in area per pond. The production of microalgae for aquaculture is generally on a much smaller scale, and in many cases is carried out indoors in 20 — 40 l carboys or in large plastic bags of up to approximately l in volume. Other closed photobioreactors such as flat panels are also being developed.
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The culture systems currently used to grow these algae are generally fairly unsophisticated. For example, Dunaliella salina is cultured in large up to approx. Similarly, Chlorella and Spirulina also are grown outdoors in either paddle-wheel mixed ponds or circular ponds with a rotating mixing arm of up to about 1 ha in area per pond. The production of microalgae for aquaculture is generally on a much smaller scale, and in many cases is carried out indoors in l carboys or in large plastic bags of up to approximately l in volume.