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Monday, 16 November 2020

Marine Algae culture

What are marine algae?

Marine algae are a diverse group of photosynthetic organisms. Generally, they live attached to hard rock and other hard substrate in coastal areas.

 Marine Algae which are considered under seaweeds are mainly divided in to 3 groups;

1.      Red algae (Rhodophyta)



2.      Brown algae (Phaeophyta)



3.       Green algae (Chlorophyta)

Why we culture marine algae? What are the benefits?

Marine algae have the potential to produce biomass and bio fuel which is a renewable resource. Algae can double their population size every few hours, so they can be harvested daily (fast growth).

  Algae consumes CO2

As any other plants, algae consume CO2 and release O2. But for high productivity algae require more CO2. So, it is favorable to the  CObalance of the atmosphere

  Algae can have high biofuel yields

Normally algae store energy in forms of oil and carbohydrates. So. they can produce 2000-5000 gallons of biofuels per acre per year

  Algae purify water

They thrive in nutrient rich waters such as urban waste (sewage), industrial waste, and effluent animal waste. They purify these waste water and produce biomass suitable for biofuel production

  Production of many by products

                 Plastics

                 Chemical feed stocks

                  Lubricants

                 Fertilizers

                 Cosmetics

  Algae culture is a pool of job opportunities 

Methods we use to culture algae

Algae can be produced according to a great variety of methods, from closely controlled laboratory methods to less predictable methods in outdoor tanks. The terminologies used to describe the type of algal culture include:

• Indoor/Outdoor

Indoor culture allows control over illumination, temperature, nutrient level, contamination with predators and competing algae, whereas outdoor algal systems though cheaper, make it very difficult to grow specific algal cultures for extended periods.

• Open/Closed

Open cultures such as uncovered ponds and tanks (indoors or outdoors) are more readily contaminated than closed culture vessels such as tubes, flasks, carboys, bags, etc.

• Axenic (=sterile)/Xenic

Axenic cultures are free of any foreign organisms such as bacteria, but this cultivation is expensive and difficult, because it requires a strict sterilization of all glassware, culture media and vessels to avoid contamination. These constraints make it impractical (and very expensive) for commercial operations. On the other hand, non-axenic or xenic cultivation, though cheaper and less laborious, are more prone to crash, less predictable, and often of inconsistent quality.

• Batch, Continuous, and Semi-Continuous

These are the three basic types of algal culture which will be described in the following sections. The next table summarizes the major advantages and disadvantages of the various algal culture techniques.

BATCH CULTURES

The most common culture system is the batch culture, due to its simplicity and low cost. The batch culture consists of a single inoculation of cells into a container of fertilized seawater followed by a growing period of several days and finally harvesting when the algal population reaches its maximum or near-maximum density. 

This is a closed system, volume-limited, in which there is no input or output of materials, that is, and resources are finite. The algal population cell density increases constantly, whereas other nutrient components of the culture medium decrease over time until the exhaustion of some limiting factor. Any products produced by the cells during growth also increase in concentration in the culture medium. 

Once the resources have been utilized by the cells, the cultures die unless supplied with new medium. In practice this is done by sub culturing, that is, transferring a small volume of existing culture to a large volume of fresh culture medium at regular intervals prior to reaching the stationary phase and the larger culture volumes are then brought to a maximum density and harvested.

Batch culture systems are widely applied because of their;

• Simplicity and flexibility

• Allowing to change species

• To remedy defects in the system rapidly

Although often considered as the most reliable method, batch culture is not necessarily the most efficient method.

Disadvantages

• Batch cultures are harvested just prior to the initiation of the stationary phase and must thus always be maintained for a substantial period of time.

• The quality of the harvested cells may be less predictable than that in continuous systems and for example vary with the timing of the harvest.

• Another disadvantage is the need to prevent contamination during the initial inoculation and early growth period. Because the density of the desired phytoplankton is low and the concentration of nutrients is high, any contaminant with a faster growth rate is capable of outgrowing the culture.

• Batch cultures also require a lot of labor to harvest, clean, sterilize, refill, and inoculate the containers.

Continuous culture

The continuous culture method, (i.e. a culture in which a supply of fertilized seawater is continuously pumped into a growth chamber and the excess culture is simultaneously washed out), permits the maintenance of cultures very close to the maximum growth rate. Two categories of continuous cultures can be distinguished:

• Turbid stat culture, in which the algal concentration is kept at a preset level by diluting the culture with fresh medium by means of an automatic system.

• Chemo stat culture, in which a flow of fresh medium is introduced into the culture at a steady, predetermined rate. The latter adds a limiting vital nutrient (e.g. nitrate) at a fixed rate and in this way the growth rate and not the cell density is kept constant.

The disadvantages of the continuous system are its relatively high cost and complexity. The requirements for constant illumination and temperature mostly restrict continuous systems to indoors and this is only feasible for relatively small production scales. However, continuous cultures have the advantage of producing algae of more predictable quality. Furthermore, they are amenable to technological control and automation, which in turn increases the reliability of the system and reduces the need for labor.

Written by: W.K.N. Shyamini





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