© 2007 IWA Publishing. Organic Waste Recycling: Technology and Management. Authored by
Chongrak Polprasert. ISBN: 9781843391210. Published by IWA Publishing, London, UK.
5
Algal production
Algae are diverse group of microorganisms that can perform photosynthesis.
They range in size from microscopic unicellular forms smaller than some
bacteria to multicellular forms such as seaweeds that may become many meters
in length. Unicellular algae are collectively called phytoplankton or single cell
protein (e.g. green algae, blue-green algae) and these are main interest in the
waste treatment and recycling processes because they are tolerant to change in
environmental conditions.
Botanists generally classify algae on the basis of (1) their reproductive
structures, (2) the kind of products synthesized and stored in the cells, and (3)
the nature of the pigments in the chromatophores. There are seven phyla of
algae as shown in Table 5.1, and examples of some planktonic algae are given in
Figure 5.1.
In most algal species the cell wall is thin and rigid. Cell walls of diatoms are
impregnated with silica, making them rather thick and very rigid. Walls of blue-
green algae contain cellulose and are semi-rigid. The motile algae such as the
euglena have flexible cell walls. The cell walls of most algae are surrounded by
a flexible, gelatinous outer matrix secreted through the cell wall. As the cells