Algal production 255Table 5.12 Total lipids in algae harvested from high rate algal ponds in Israel (Aaronson
et al. 1980)
Major species Total lipids (% of dry weight) Neutral lipids (% of dry weight)
Chlorella 22.6 10.9
Euglena 11.0 8.9
Micractinium 17.4 6.0
Oocystis 19.9 13.5
Scenedesmus 22.2 10.4
Reproduced by permission of Elsevier Science Publishers B.V.
5.5 Public health aspects and public acceptance
5.5.1 Public health risks
Production of waste-grown algae involves some public health risks due to:
- Contamination of the pathogens normally presents in raw wastes,
and - Accumulation of heavy metals and other toxic compounds in algae
cells.
As discussed in section 5.1, pathogen die-off in the algal ponds can take
place due to the ultra-violet light, algal toxins produced by algae cells,
competition with other micro organisms, inhibitory environments such as high
pH during photosynthesis, and sedimentation with sludge. However, a complete
removal of pathogens never exists in practice, because they may be protected by
self-shading of algae and clumping with sewage solids.
Edwardset al. (1981b) found the microorganism removal in their HRAP unit
located in Thailand to be about 1 order of magnitude. The ranges of bacterial
densities in the HRAP effluents were 1.0x10^5 - 1.3x10^10 , 1.6x10^5 - 2.4x10^6 , and
7.0x10^4 - 9.2x10^5 no./100 mL for the standard plate count bacteria, total
coliforms and fecal coliforms, respectively. According to Table 2.27, this HRAP
effluent is not suitable for unrestricted irrigation (e.g. irrigation of edible crops),
but may be used for restricted irrigation such as irrigation of trees and other
industrial crops.
Care should be taken on occupational risks to the people working with HRAP
units. The possibility of contamination to these people is high, particularly
during algal harvesting which may lead to the spreading of pathogens to other
people by carrying with body or clothes. The possibility of swallowing
pathogens during the working period cannot be ruled out. Therefore it is always