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Datasheet

Flasks

Summary

  • Last modified
  • 17 April 2018
  • Datasheet Type(s)
  • Growout System
  • Preferred Scientific Name
  • Flasks
  • Overview
  • Types of Algal Cultivation Vessels

    Seed supply propagation flasks: Round flask or other geometrical shapes, 1-10 L

    ...

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Pictures

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PictureTitleCaptionCopyright
300 litre polyethylene bags with algal culture, illuminated from the side with fluorescent tubes.
TitleAlgal culture bags
Caption300 litre polyethylene bags with algal culture, illuminated from the side with fluorescent tubes.
CopyrightJosianne G. Støttrup
300 litre polyethylene bags with algal culture, illuminated from the side with fluorescent tubes.
Algal culture bags300 litre polyethylene bags with algal culture, illuminated from the side with fluorescent tubes.Josianne G. Støttrup
3000 litre fibre glass tank with high pressure sodium lamps.
TitleFibre glass tank
Caption3000 litre fibre glass tank with high pressure sodium lamps.
CopyrightJosianne G. Støttrup
3000 litre fibre glass tank with high pressure sodium lamps.
Fibre glass tank3000 litre fibre glass tank with high pressure sodium lamps.Josianne G. Støttrup
Artificially illuminated photbiorectors for in-door use, produced by BioProcess. The reactor volume is 600 litres and illumination is provided by 2-4 kW of fluorescent lighting placed on the inside of the white reflecting  cylindrical back plates.
TitleArtificially illuminated photbiorectors
CaptionArtificially illuminated photbiorectors for in-door use, produced by BioProcess. The reactor volume is 600 litres and illumination is provided by 2-4 kW of fluorescent lighting placed on the inside of the white reflecting cylindrical back plates.
CopyrightJosianne G. Støttrup
Artificially illuminated photbiorectors for in-door use, produced by BioProcess. The reactor volume is 600 litres and illumination is provided by 2-4 kW of fluorescent lighting placed on the inside of the white reflecting  cylindrical back plates.
Artificially illuminated photbiorectorsArtificially illuminated photbiorectors for in-door use, produced by BioProcess. The reactor volume is 600 litres and illumination is provided by 2-4 kW of fluorescent lighting placed on the inside of the white reflecting cylindrical back plates.Josianne G. Støttrup
Fermentation plant with 3 m³ and 10 m³ reactors. Smaller tanks to the right are substrate reservoirs (concentrated medium).
TitleFermentation plant
CaptionFermentation plant with 3 m³ and 10 m³ reactors. Smaller tanks to the right are substrate reservoirs (concentrated medium).
CopyrightJosianne G. Støttrup
Fermentation plant with 3 m³ and 10 m³ reactors. Smaller tanks to the right are substrate reservoirs (concentrated medium).
Fermentation plantFermentation plant with 3 m³ and 10 m³ reactors. Smaller tanks to the right are substrate reservoirs (concentrated medium).Josianne G. Støttrup
Tubular reactor plant with two horizontal layers of tubes (diameter 0.1 m; length of loops 400 m. Total volume: 4 m³.
TitleTubular reactor plant
CaptionTubular reactor plant with two horizontal layers of tubes (diameter 0.1 m; length of loops 400 m. Total volume: 4 m³.
CopyrightEmilio Moina Grima/Almeria University, Spain
Tubular reactor plant with two horizontal layers of tubes (diameter 0.1 m; length of loops 400 m. Total volume: 4 m³.
Tubular reactor plantTubular reactor plant with two horizontal layers of tubes (diameter 0.1 m; length of loops 400 m. Total volume: 4 m³.Emilio Moina Grima/Almeria University, Spain
Flat plate reactor.
TitleFlat plate reactor
CaptionFlat plate reactor.
CopyrightOtto Pulz/IGV, Germany
Flat plate reactor.
Flat plate reactorFlat plate reactor.Otto Pulz/IGV, Germany
Rotifer stock cultures kept in closed vials on a rotor are fed with algae.
TitleRotifer stock cultures
CaptionRotifer stock cultures kept in closed vials on a rotor are fed with algae.
CopyrightLaboratory of Aquaculture & Artemia Reference Center
Rotifer stock cultures kept in closed vials on a rotor are fed with algae.
Rotifer stock culturesRotifer stock cultures kept in closed vials on a rotor are fed with algae.Laboratory of Aquaculture & Artemia Reference Center
Conical flasks and carboys of algae used for algal production prior to inoculating larger batch bags or tanks.|Conical flasks and carboys of algae used for algal production prior to inoculating larger batch bags.
TitleConical flasks and carboys of algae
CaptionConical flasks and carboys of algae used for algal production prior to inoculating larger batch bags or tanks.|Conical flasks and carboys of algae used for algal production prior to inoculating larger batch bags.
CopyrightChristopher J. Cutts
Conical flasks and carboys of algae used for algal production prior to inoculating larger batch bags or tanks.|Conical flasks and carboys of algae used for algal production prior to inoculating larger batch bags.
Conical flasks and carboys of algaeConical flasks and carboys of algae used for algal production prior to inoculating larger batch bags or tanks.|Conical flasks and carboys of algae used for algal production prior to inoculating larger batch bags.Christopher J. Cutts

Identity

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Preferred Scientific Name

  • Flasks

International Common Names

  • English: Bags; Fermenters; Photobioreactors; Tanks; Vessels

Overview

Top of page Types of Algal Cultivation Vessels

Seed supply propagation flasks: Round flask or other geometrical shapes, 1-10 L

Outdoor cultivation vessels:

  • Raceways / ponds
  • Photobioreactors

    • Tubular photobioreactors
    • Flat-plate photobioreactors
    • Spherical photobioreactors

In-door cultivation vessels:




    • Plastic bags
    • Transparent cylinders
    • Rectangular tanks – illuminated from above or from the side
    • Fermenters

 


Outdoor Versus In-door Cultivation


With outdoor cultivation, natural daylight is used for photosynthetic production in either open vessels or closed photobioreactors. This is quantitatively far the most significant production form and comprises both independent industrial productions of microalgae for human food supplements (Spirulina, Chlorella and Haematococcus production) and a part of the microalgal feed production in large bivalve hatcheries. In-door cultivation for feed production or large volume starter cultures for outdoor propagation is practiced in bivalve, shrimp and fish hatcheries. In-door green-house production may also depend (totally or partly) on natural daylight, or, the production is entirely depending on artificial illumination as it is most often the situation in Nordic bivalve or fish hatcheries where hatchery activities most often are most intense during the dark season.

Electricity costs for artificial illumination are very significant; but so is also the depreciation and maintenance on the illumination systems. On the other hand, volume productivity of the photobioreactor systems and photosynthetic efficiency is much higher than in solar systems where the diurnal illumination and temperature variability makes efficient light utilization very difficult to achieve.

 


Out-door Systems

Photobioreactors


There are 3 major types of closed photobioreactors in use to day; tubular photobioreactors, flat panel photbioreactors and the dome photbioreactor. Tubular and dome bioreactors are now in regular use for a significant production of astaxanthin with Haematococcus, whereas the flat panel is largely still at the experimental stage.

The reason for developing such photobioreactors is the requirement of a protected environment for algae that cannot otherwise be selectively bred.

The tubular photobioreactor was the first closed bioreactor that was developed for outdoor industrial production purposes and was based on the works by John D. Pirt (Pirt et al., 1983). With the tubular photobioreactor it is possible to construct a large, low-cost reactor with cheap plastic pipe-work and support structures. Several attempts have been made to exploit this but most have encountered insurmountable technical and culture management obstacles. A number of tubular designs have been applied by engineering companies and marketed with some success; the "Biocoil", originally designed by Biotechna Graesser A.P. Ltd.,UK (Watanabe and Hall, 1995; Borowitzka, 1999; Richmond, 2000). The Biocoil is a helical arrangement of PVC tubing, built in various sizes, the "Biofence" from Variconaqua, UK: vertically stacked horizontal loops of PVC tubing. Custom built designs include various horizontal single-layer loops of PMMA or glass or disposable light plastic material. Also vertically stacked horizontal loops similar to the Biofence but with different materials and construction techniques have also been devised. A small number of plants based on the tubular reactor are now in regular production, including the astaxanthin plants of Mera pharmaceuticals (Hawaii) and Algatechnologies (Israel) and the Chlorella producing plant and the Steinberg production plant in Klötze, Germany.

The combined annual production from the Hawaiian and Israeli plants is about one metric ton of astaxanthin, corresponding to about 50 tons of Haematococcus biomass whereas the German Chlorella plant recently has resumed operations (2004) after financial reconstruction and production information is therefore not yet available. The lay-out of the principle is variable; and both horizontal linear, vertical linear and cylindrical-helical positioning of the tubes have been made. For Haematococcus, the horizontal lay-out which optimises insulation but is the most expensive to build, is preferable for the product formation step because this phase requires high insulation.

The dome photobioreactor was developed by S. Hirabayashi in the early 1990s (Hirabayashi et al., 2002) in the Japanese company Micro Gaia operating at Hawaii. Fuji Chemical Corporation Ltd., which is the parent company to Microgaia, operates 1000 of these domes at Hawaii for the production of astaxanthin.

The flat plate/alveolar panel reactor originated from the work of M.Tredici, R. Materassi and others at the Dipartimento di Biotecnologie Agrarie, Università di Firenze and was first described in 1991 (Tredici et al., 1991; Tredici and Materassi, 1992). A recent version has been patented and a system being built to produce Nannochloropsis at a fish hatchery in Tuscany (M.R. Tredici, personal communication).

This photobioreactor construction principle has been extensively applied in microalgal solar production research and development as it offers a unique opportunity to estimate absorption of solar radiation because of its simple plane geometry but has until now not been applied in a full scale industrial applications.

 


In-door Systems



  • Plastic bags
  • Plastic cylinders
  • Fermenters

Plastic Bags


A large number of minor hatcheries, particularly Nordic-temperate areas use suspended plastic bags as a grow-out system for cultivation of feed-microalgae for bivalves, fish and shrimp larvae. Also, algae for green water fish larval tanks in intensive fish hatcheries frequently are produced in hanging plastic bags. In terms of number of systems/producers, the plastic bags are the most important system applied. However, the quantities of biomass produced in these systems are limited and insignificant and very costly, compared to the production of Chlorella, Spirulina and Haematococcus for human food supplements. In a questionnaire investigation of algal culture practices in 42 hatcheries Coutteau and Sorgeloos (1992) estimated the cost of algal production to between 100 and 400 $US kg-1 DW and the produced quantities were mostly under 1 kg DW day-1. The cost of algal production represents about 30 % of the total production costs in the hatchery (Coutteau and Sorgeloos, 1992).

The high cost is partly electricity costs for illumination ($US 50-200 kg-1 DW), partly labour costs which are very significant in small operations. Plastic bag systems are usually applied for small product requirements: production levels around one kg DW day-1, or a couple of cubic meters of culture volume (maximum biomass density in well managed, artificially illuminated plastic bags is in the range 0.2-0.5 kg M-3). All current micro algal species may be cultured in plastic bags as both illumination and stirring is implemented in a gentle manner. Large plastic bags (3-400 L) are shaded from the support structures (grid). Unsupported plastic (100-150 L) are not shaded, but a trade-off using smaller bags is the increased labour associated with the management of the increased number of bags.


Transparent Cylinders


Another cultivation vessel used in a production mode similar to the plastic bags, is the transparent cylinder. The cylinder is typically made from highly transparent fibreglass and is typically a larger volume than the plastic bags which result in lower maximum biomass density. These vessels are illuminated from the side as are the plastic bags. Illumination loss arise from low transparency of the construction materials (60-90 %). Transparent cylinders are useful for slightly larger daily production requirements than in the case of the plastic bags.


Tanks


Top-illuminated non-transparent tanks are typically seen in hatcheries with larger production requirements.

The world’s largest bivalve hatchery, Coast Oyster (Washington) uses partly artificially illuminated in-door tanks for its phytoplankton production. At Coast Oyster, the larval production is 30 x 109 eyed larvae per year and this requires about 1.2 tons of algae (DW). The cost of this production is estimated to about $US 50 kg-1 (Duerr et al., 1998). Though this figure ranks lowest in published hatchery microalgal production cost figures, it is still one order of magnitude higher than the production costs in the large out-door facilities.


Fermenters


Fermenter production of microalgae is mainly practiced in Japan. About half the Japanese Chlorella production is now carried out in fermenters (H. Endo, personal communication), suggesting about a thousand metric tonnes. Outside Japan, the US based company Martek Corp. has a significant production of Schizochytrium sp., a primitive microalgal species used for production of DHA rich oil for human food supplementation. The heterotrophic production is carried out in conventional fermenters using glucose as a carbon source. The company in 2004 had 3000 M3 of reactor volume and about 600 employees and generated revenues of about $US 200. The production of biomass is not disclosed but would not be significantly different from that of the combined Japanese Chlorella production.

In Europe, a British company, Celsys for a while had a production of dried Tetraselmis suecica, produced by fermentation. The cost of the product was $US 170 kg-1 and the product gained some approval for use as a bivalve hatchery supplement diet, but was considered too costly in regular use and product and company was discontinued in 1998. Another approach to fermentative microalgal production was the continuous mixotrophic production of Haematococcus (photosynthesis + acetate respiration), developed by the Danish-Icelandic BioProcess, which was established in large volume pilot scale, but never made it into routine production. The company ceased its operations in 2003.

Structure and Design

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Seed supply propagation flasks: Round flask or other geometrical shapes, 1-10 L.

 




Flask type may vary but is typically either transparent polycarbonate flasks or round flat-bottomed glass flasks. Sizes from1-20 L. 20 L is the largest size that may be manipulated by laboratory staff without hoist systems. Flask and assembly also need to be autoclavable.

A typical assembly is a stopper or screw-cap with 3-5 ports:

medium supply

aeration (mixing, degassing)

gas escape

culture harvest

inoculation

Medium supply is typically a flask with ready-made medium. Medium supply is also sterilized either by autoclaving or sterile filtration.

 


Feed (Input to the Cultivation Process)

Feeds to the cultivation process (not including fermentation, which has been described separately), include:

Medium

Air

Carbon dioxide

Light


Medium


Base Medium, Water Treatment


The base medium is either freshwater or filtered natural seawater, but artificial seawater may also be used. For Spirulina, a high alkalinity media (made up from a mixture of sodium hydrogen carbonate and sodium carbonate) may be used to ensure competitive exclusivity. To produce Dunaliella under similar conditions of competitive exclusivity, a fortified sea water (concentrations of sea salt higher than normal seawater) medium may be used, dissolving evaporated sea salt in the base medium (fresh water or normal seawater).

Completely defined seawater media (made up of pure chemicals) are generally only used for research purposes whereas seawater media based on evaporated natural sea water may be economical in use in small operations. A comparison of different artificial sea water media is given by Berges and Franklin (2001).

Filter systems usually comprise sand filters, followed by industrial type deep-bed cartridge filter systems, typically with a particle retention down to 10 µm. This will eliminate most harmful organisms (protozoans and other algae) from the water. Membrane filtration is sometimes added as a final step for preparation of pure seawater in relatively small quantities. This may be important for producing starter cultures for large tanks. The base medium is most often spiked with nutrient solution to produce the final culture medium, directly in the cultivation tank. This medium is normally common to both stock cultures, starter cultures and grow-out cultures.


Final Culture Medium


The different species of microalgae that are used in aquaculture and included in Table 1. have rather little different medium requirements (apart from the base medium) and for most purposes the f/2 medium maybe (and is) used (Guillard and Ryther, 1962). For diatoms, the version that includes silica, is required. Otherwise, silica may be omitted. Frequently; the base medium, is supplemented with nutrients, and added as a concentrated solutiondirectly in the cultivation vessel, allowing the micro algae to grow into dense cultures. The nutrient solutions consists of inorganic macro- and micro nutrient salts, with possible addition of necessary vitamins.

For the requirement of a number of the marine flagellates, including Isochrysis, B12 and thiamin is added to the nutrient solution. Some recipes also contain biotin.

Another medium also frequently used, is the Walne medium (Walne, 1974).


Air


Compressed air from a blower (0-0.05 bar pressure) will suffice for smaller tanks. However, to deliver compressed air to tanks deeper than 3 m, the blower will not have sufficient pressure and a compressor is required.

The compressor should deliver oil-free air (either, the compressor should be lubrication-free or the air should be filtered through hydrophilic filters to remove oil vapours. Normal compressor gear for this purpose is not sufficient.


Carbon Dioxide


Carbon dioxide may be delivered to the culture from pressure bottles or for large applications, from an open cooled liquid carbon dioxide tank.

The carbon dioxide may for most purposes be mixed directly into the air at approximately 0.5 %. This will suit growth (illumination) optimized cultures. Alternatively, the CO2 may be added on demand to control pH by a pH meter.


F/2 Recipe (from CCAP home page):


NaNO3 0.075 g

NaH2PO4., 2H2O 0.00565 g

Trace metal solution (1) 1.00 ml

Vitamin solution (2) 1.00 ml

Salt water 1 L

1) Trace metals stock solution (chelated) per litre

EDTANa2 4.360 g

FeCl3.6H2O 3.150 g

CuSO4.5H2O 0.010 g

ZnSO4.7H2O 0.022 g

CoCl2.6H2O 0.010 g

MnCl2.4H2O 0.180 g

Na2MoO4.2H2O 0.006 g

(2) Vitamin mix stock solution per litre

Cyanocobalamin 0.0005 g

Thiamine HCl 0.1 g

Biotin 0.0005 g

(3) Sodium metasilicate stock solution: per litre

Na2SiO3.9H2O 30.0 g


Light


In-door


Most hatchery microalgal cultures are illuminated by fluorescent tubes. Fluorescent tubes deliver the most economic light – (modern T5 fluorescent tubes deliver about 100 lumen per watt). But for most applications, the fluorescent light tubes are not always easy to apply in a cost effective manner. Luminaires, equipped with reflectors or simple reflecting (white) back plates, involve a substantial loss of light and also in the transition of light from the luminaire to the culture, substantial losses are encountered. With fluorescent light tubes installed in closed luminaires, it is not unusual that 60% of the light flux is lost in transition.

Free fluorescent tubes, surrounded by all sides by thin hanging bag cultures, constitute probably the most light-economical installation.

Monofilament or discharge lamps offer in some cases - such as high pressure sodium lamps – almost the same light flux per watt and the transition losses may be much smaller.

The growth economy, considering the illumination, eventually absorbed by the culture, is very high with fluorescent light. More than 30% of the theoretically possible maximum yield from fluorescent light may be achieved in well managed cultures. This corresponds to an out-door yield on a sunny 12 hour day of 85 -100 g DW m-2.


Out door


Trapping the energy of the solar radiation at high efficiency is a challenge that drives the development of new photobioreactors.

The solar radiation from a blue sky in a plane perpendicular to the rays is about 2100 µE m-2 sec-1. Most algae are light saturated at levels < 100-200 µE m-2 sec-1 (Haematococus is for example saturated at about 50 µE m-2 sec-1) and considering that illumination over saturating levels not only is wasted but at higher sustained levels directly detrimental to the cells, it is understandable that utilization of sunlight at high photosynthetic efficiency, is difficult. Temperature is important also to the utilization of light. At low temperatures, typically prevailing in the morning in open pond cultures, the algae will saturate at much lower levels than at high temperatures.

The maximum theoretical productivity on a 12-hour sunny day should be around 2 x 102 g DW M-2. Sustained productivities from microalgae in well managed tanks and raceways are normally about 25 g DW M-2 day-1 for Spirulina and Chlorella (Lee, 2001), and similar levels are reached with photobioreactors also for algal species that grow less well in open systems than Chlorella and Spirulina.

Levels of 50-130 g DW M-2 day-1 are rare but have been realised with Spirulina and Chlorella pyrenoidosa (Lee, 2001).

It should be noted that cloud cover may reduce the photosynthetically active radiation (PAR) considerably. Heavily clouded days may result in light intensity levels of less than 100 µE m-2 sec-1.

When considering a site for placing an out-door algal cultivation plant, cloud cover is one of the most important factors determining the potential productivity of the plant.

Seed Supply and Species Availability

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The range of species used in aquaculture or human food supplements, is given in Table 1.

The table is based on the list of species of algae for aquaculture of Muller-Feuga et al. (2003) with the addition of some human food application species.

. List of commonly used algal species


ClassGenusSpeciesUse (Aquaculature,Human food appl.)
CyanophyceaeArthrospira (Spirulina)platensis, maximaAq, Hu
 Aphanizomenonflos-aquaeHu
BacillariophyceaeSkeletonemacostatum, pseudocostatumAq
 PhaeodactylumtricornutumAq
 Chaetoceroscalcitrans (/pumillum),gracilis,Aq
 Thalassiosirapseudonanna, weisflogiiAq
ChlorophyceaeChlorellaminutissima, virginica, grossiiAq
  pyrenoidosaHu
 Dunaliellatertiolecta, salinaHu, Aq
 NannochlorisatomusAq
 HaematococcuspluvialisHu, Aq
PrassiophyceaeTetraselmissuecica, striata, chuiiAq
 PyramimonasvirginicaAq
CryptophyceaeRhodomonasbaltica, salina, reticulataAq
EustigmatophyceaeNannochloropsisoculataAq
PrymnesiophyceaeIsochrysisgalbana, T. IsoAq
 Pavlovalutherii, salinaAq
DinophyceaeCrypthecodiniumcohniiAq, Hu
ThraustochytriidaeSchizochytriumsp.Aq, Hu
    

 


Availability of Species

All species currently used in aquaculture or for human nutritional purposes are available from various culture collections. However, it should be noted that some microalgal species in industrial production (e.g. Schizochytrium and Haematococcus) have been improved genetically by the companies applying them and are only available as wild types from strains collections.

Some of the most frequently used culture collections are given in Table 2.

2. List of frequently used culture collections


Name of institutePostal addressTelephoneWeb / e-mail contactContact person
Algobank,Algobank-Caen Université de Caen Basse-Normandie Esplanade de la Paix 14032 Caen cedex France+0033 2 31 56 53 46http://www.unicaen.fr/algobank/FR/algobank/contact1.phpDr. Benoît Véron
CCAPCulture Collection of Algae and Protozoa Dunstaffnage Marine Laboratory OBAN Argyll PA37 1QA Scotland, United Kingdom  +44 (0)1631 559000 CCAP@sams.ac.ukhttp://www.ccap.ac.uk/about_us/find_us.htmDr. John Daymailto:john.day-sams@sams.ac.uk
CSIROCSIRO Marine Research GPO Box 1538 Hobart, Tasmania, 7001 Australia(03) 6232 5316http://www.marine.csiro.au/microalgae/supply.htmlCathy Johnston
NIES, Japan (MICROBIAL CULTURE COLLECTION AT NATIONAL INSTITUTE FOR ENVIRONMENTAL STUDIES)MICROBIAL CULTURE COLLECTION National Institute for Environmental Studies 16-2 Onogawa, Tsukuba, Ibaraki, 305-8506 JAPAN  http://www.nies.go.jp/biology/mcc/home.htm e-mail: mcc@nies.go.jp 
Sammlung von Algenkulturen University of GöttingenSammlung von Algenkulturen Albrecht-von-Haller-Institut Universität Göttingen Nikloausberger Weg 18, 37073 Göttingen Germany http://www.epsag.uni-goettingen.de/html/sag.htmlDr. Maike Lorenz mailto:mlorenz@gwdg.de
CCMP (Provasoli Institute, Maine, USA CCMP, Bigelow Laboratory for Ocean Sciences P.O. Box 475, 180 McKown Point Road, West Boothbay Harbor, Maine 04575 USA(001) 207 633 9630http://ccmp.bigelow.org/Julianne P. Sexton, Curator e-mail: jsexton@bigelow.org
UTEX(University of Texas, US) The Culture Collection of Algae (UTEX), 1 University Station A6700 Austin, TX 78712-0183, USA (512) 471-4019http://www.bio.utexas.edu/research/utex/Toni Henningmailto:utalgae@uts.cc.utexas.edu
The Roscoff Culture CollectionBrittany, FranceStation Biologique, BP 74, F-29682 Roscoff, France http://www.sb-roscoff.fr/Phyto/RCC/index.php 

Processing and Products

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The processed industrial products currently made from microalgae are:

- production of human food supplements from Chlorella, Spirulina, Aphanizomenon and Haematococcus,

- oils and oleoresins

- fine chemicals

- algal pastes for aquaculture feeds.

Human food supplements are to a large extent concentrated and dried biomass, stabilized and put into tablet form. Stabilizing includes microbiological stabilizing (pasteurization) and prevention of oxidation by the addition of antioxidants.

For methods of concentrating, see section on 'Harvesting Strategies'.

In the case of drying, mainly spray drying is applied. Other applicable processes include freeze drying that is less detrimental to the product, but also more costly.

For extraction of oils, both hexane extraction and super critical carbon dioxide extraction are applied.

An oleoresin is an oil emulsion of the raw biomass that may increase the concentration of lipophilic materials such as carotenoids 2- to 5-fold, thereby reducing the necessary tablet size.

Harvesting Strategies

Normally, microalgae in aquaculture are not concentrated at harvest but applied directly to the larval cultures for which they are produced.

For human food supplements, production of fine chemicals and algal pastes, however, the algae must be concentrated. Two techniques are in use: centrifugation and flotation. With centrifugation, large semi-continuous centrifuges (continuous feeding, intermittent retrieval of algal cake) are applicable. Fully continuous centrifuges imply that the product is forced through a small orifice under large shear forces and pressure gradients and may not be applicable to all species.

Flotation involves injection of gas-saturated medium that release small gas bubbles that lift and clog the algal cells. Coagulating substances (for example polymers) may be added to enhance and stabilize the process (Garcia et al., 2000; Grima et al., 2003). This procedure is not very common, but, unlike the centrifugation, is very gentle and has been tested and found applicable for production of algal pastes (D'Souza et al., 2002).

Impact: Environmental

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Environmental impacts of the cultivation of microalgal cultures are difficult to assess. The direct impact is minimal, but indirect positive impacts may be registered when considering microalgal cultivation as a part of intensive aquaculture which is an alternative to other less environmentally friendly practices.

Reduction of the use of medicinal compounds in various larval cultures through the green water technology application of micro algae. A summary of these effects may be found in Muller-Feuga et al. (2003). By using Chaetoceros as an Artemia enrichment bacterial load on Artemia (gut and surfaces) were reduced 97 % compared to emulsion enrichment diets (Olsen et al., 2000; Tolomei et al., 2004). This value was comparable to un-enriched (starved) Artemia so it is possible to enrich the Artemia with the algae without simultaneouly increasing the bacterial load of Artemia. This will reduce the requirement for bacteriostatic chemicals or antibiotics in the larval rearing.

Reduction of negative environmental impact of extensive shrimp farming is obtained by transition to intensive shrimp farming that requires micro algal production.

Hatchery use of microalgae in bivalve culture. Grow-out phase of bivalve culture takes place in the natural environment and has a positive impact in nutrient load on coastal zones.

Growout Management

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Many aspects of the algal culture management have been described in other sections, including water sources and treatment which is considered a feed item for the cultivation system.

 


Water Disposal and Recirculation

Waste Water Disposal from Algal Culture


In aquaculture, there is no direct waste disposal requirement with micro-algal cultures. The entire algal culture is normally added as a direct feed to the larval tanks and will hence not produce any direct wastes, and water from the algal cultures will only constitute a small fraction of the waste water from the fish or bivalve tanks.

With production of human food supplements and algal paste products for aquaculture, the harvested cultures are concentrated and the water from that process constitutes a primary waste water source. There is no information available to indicate that these water streams are currently re-used or reprocessed. Waste water streams from micro-algal cultures are unproblematic as no chemical or antibiotic agents are added and may be disposed of by local municipal waste water systems.

 


Integrated Algal Culture

However, there is a case for re-use of waste water streams from production of fish or bivalves for micro-algal cultivation particularly from recirculated plants as these waste streams will contain significant quantities of mineralized nutrients (Borges et al., 2005).


Polyculture Systems


Algal growth may be integrated into fish aquaculture systems, either as separate pond systems, such as the patented PAS: Partitioned Aquaculture System (Brune et al., 2003), or by co-culturing herbivorous fish species and optimizing the conditions for algal growth within the same pond system (Ludwig, 1996; Wang et al., 1998; Azim et al., 2002). The algal metabolism reduces ammonia levels thereby allowing increased fish stocking densities. Catfish production in a normal aerated pond can reach a level of about 5600 kg ha-1; this figure includes increased stocking and feeding allowed by normal algal growth but with the PAS system, fish productivity may reach 33600 kg ha-1 (Brune et al., 2003). In such systems, however, extended dense cloud cover may cause the ammonia level to rise. Aeration to prevent nocturnal oxygen depletion must also be taken into consideration.

 


Wastewater Treatment Systems

In the 1970s, significant efforts were devoted to develop micro-algal recirculation of tertiary treated municipal waste water. Whereas micro-algal treatment ponds play an important role in nutrient polishing of such streams in many countries, re-use of the nutrients from such streams in the form of algal biomass has not attained any practical role because of public health regulatory difficulties. Investigations of these possibilities, however, are still in progress (Chevalier et al., 2000; Garcia et al., 2000).


Other Wastes


For artificially illuminated micro-algal cultures, there is a disposal requirement for used lamps. Fluorescent tubes have a lifetime of about 1.5 years whereafter the light output falls significantly. Many lamps, including fluorescent tubes, contain small quantities of heavy metals (the fluorescent tubes contain small quantities of mercury) that must be dealt with in an environmentally responsible way, considering the large quantities of waste fluorescent tubes a large algal cultivation unit will generate.

Another waste stream may be used plastic bags, the material, most often used, however is polyethylene that may be safely incinerated.

 


Stocking Strategies

Density at Stocking


With most batch cultures, short duration culture cycles and hence high stocking densities are preferable for two reasons: first, the frequency of critical contamination and consequently loss of the culture is diminished and second, efficiency of exploitation of the cultivation and illumination is improved. A cycle corresponding to two or three doublings of the cell numbers is therefore typically applied. Actual stocking numbers (in terms of cell numbers) vary according to species and light path (~size of cultivation vessel). In most hatcheries, however, cell numbers are rarely followed routinely. Instead, as a routine measure, the colour intensity of the culture is regulated and observed.

 


Starter Culture Propagation

Propagation of starter cultures may be carried out from seed cultures directly (using aseptic flask techniques described in the section 'Seed supply propagation flask (1)'. However, these cultures are very labour intensive and often the bottle neck in hatcheries. Leaving a certain fraction of a harvested culture and topping up with fresh medium (semi-continuous technique) is therefore frequently applied. This requires that the culture in question is sound and contamination level is low and the outcome depends on the judging ability of the hatchery manager. The use of, for instance, small plastic bag cultures as starter cultures for large plastic bags or other large volume cultures is also applied.

When the final growout culture vessel is situated outdoors, it is often referred to as a bloom culture.

 


Cultivation Strategies

Batch


A batch culture that is grown from an inoculated volume of fresh medium and later totally harvested.


Fed Batch


A fed batch culture is a batch that at a certain biochemical constitution is fed a volume of medium to affect the physiological state of the culture, for instance, to induce formation of a certain product.


Continuous Culture


A continuous culture is a culture that is started and when grown up, diluted continuously and thereby kept at a constant volume. If the dilution rate is less than the maximum growth rate of the algal culture under the given circumstances, the culture density will attain a constant biomass density, the so-called steady state level. In principle, such a culture may continue producing at constant levels. This principle ensures maximum light utilization and maximum volume productivity, but for long duration culture cycles, it is required that the set-up and various feeds to the culture are absolutely grazer free. Absence of bacterial contamination is not an absolute requirement as bacterial growth in well-managed algal cultures normally remains very low because of low levels of dissolved organic substances in such cultures. If the continuous culture however, is subjected to, for instance, nutrient limitation, the microalgae may produce extracellular levels of organic substances that can support vigorous growth of bacteria. A cultivation plant may be built from relatively cheap materials that can keep producing for years without re-inoculation. Plants have been marketed that applied this principle for vessels up to 600 L, such as the one from the Danish company BioProcess that has ceased trading or the British company, Seasalter. The latter is based on open plastic bag cultures.


Semicontinuous Cultures


A continuous culture that is fed/harvested at discrete intervals.

 


Yield - Measures of Productivity

Yield


The term yieldindicates a resulting quantity per volume, i.e. kg of product per cubic meter of vessel volume (kg/M3 ) or, for a defined volume of a given cultivation vessel, referring only to a quantity.


Productivity


Productivity is either volumetric: yield per time, units for instance, kg DW M-3 day-1 or area-based: quantity of biomass produced per area unit per unit time (for instance kg DW M-2 day-1). Area yields are most relevant for out-door solar productions while volumetric productivities are most relevant for artificially illuminated culture volumes.


Growth


Exponential growth rates are often indicated, as for instance denoted by the symbol µ. The unit of µ is time-1.

If the growth rate of a batch is constant over an interval t0 – t1, and X represents the biomass, the biomass at t1 in biomass will be X1 = X0 exp(µ (t1 - t0)).

Inversely, the growth rate may be calculated from µ = ln(X1)-ln(X0) / (t1-t0).

The instantaneous productivity of a batch culture is µ * X. The productivity of a continuous culture at steady state is constant.

Values of growth rates of a number of different algae in different systems applied in aquaculture may be found in Mueller-Feuga et al. (2003).

 


Disease Prophylaxis

Microalgal culture is a very young practice and there is not yet an established concept of disease prophylaxis. Disease could be considered equivalent to culture crashes, a concept that denotes an unexplained bleaching or growth arrest of the culture that subsequently is discarded. In many cases, the introduction of grazers, like ciliates may be the cause of culture crashes. Means of avoiding contamination of cultures with grazers include proper cleaning and disinfection of permanent culture vessels between culture cycles, minimizing the length of culture cycles and regular cleaning of any tools used with the algal cultures, such as pumps and tubing. Air injected in the cultures for stirring is usually filtered to avoid contaminants and water for making up medium is UV-sterilized and/or filtered to a variable degree (1 µM is readily obtainable with large cartridge filters). UV sterilization is very inefficient with large organisms, however, and these are the more troublesome contaminants.

Marketing

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Marketing of human food supplements from microalgae is still rather limited; an exception is the marketing of Chlorella and Spirulina products that are common products in most health shops and pharmacies. Lately, also the DHA rich oil from Martek has reached health shops and pharmacies. Other microalgal food supplements are either marketed directly on the internet by the producers or other internet marketing operators.


ß-carotene from Dunaliella is sold in bulk by the German fine chemicals supplier, Cognis Gmbh.

References

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Contributors

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Main Author
Josianne Stottrup
Danish Institute for Fisheries Research, Dept. of Marine Ecology and Aquaculture, Kavalergården, Charlottenlund Castle, DK-2920 Charlottenlund, Denmark

Main Author
Sunil Siriwardena
Institute of Aquaculture, University of Stirling, Stirling, FK9 4LA, UK