Algal production 223adverse environment prevailing in the pond. Adverse environment to pathogens
is caused by:
- Diurnal variation of pH due to photosynthesis,
- Algal toxins excreted by algae cells, and
- Most importantly, solar radiation (UV light)
At present, the main attractiveness of algal mass cultures is that they have
great versatility to be integrated into multi-use systems for simultaneously
solving several environmental problems. Figure 5.2 shows possible applications
of the algal mass cultures, the details of which are described in section 5.4.
Since algal mass culture systems must be large and exposed to the outdoor
environment, it greatly magnifies the bioengineering problems involved.
Specific problems relating to culture mixing, nutrient availability and addition,
species control, algal separation and harvesting have been of major concern, as
outlined below.
Harvesting
Algae are very small in size (ranging from 1 to several ȝm), difficult to harvest
and requiring skilful operation. The existing technologies of algal harvesting are
normally complex and expensive, and will be discussed in section 5.3.
The economical method of harvesting of algal cells from algal pond is still
under research.
Algae composition
Except Spirulina, algae have thick cell wall, which makes the untreated algae
indigestible to non-ruminants. Therefore before feeding to animals, algae cells
have to be ruptured by:
- Chemical alteration of cell wall by acid treatment, or
- Mechanical or thermal treatment for cell wall destruction.
Another factor limiting the consumption of waste-grown algae is nucleic acid
present in algae cells (4-6%), which may be harmful to human bodies (Becker
1981).
To produce algal biomass for animal or human consumption, the blue-green
algae,Spirulina (Figure 5.3), is the desirable species to be cultured because its
cell wall is more digestible by non-ruminants and its filamentous cells are easier
to be harvested. Mass culture of pure species of Spirulina requires certain
environmental conditions (e.g. pH and nutrients) conducive to its growth
without contamination from other microbes. Algal ponds or high-rate ponds
treating wastewater will contain several algal and bacterial species essential for