254 Organic waste recycling: technology and management
Since algae are capable of fixing nitrogen from atmosphere, they have an
important role in agriculture. It was reported that rice field inoculated with the
nitrogen fixing algae Tolypothrix tenvis for four years produced 128% more
crop than uninoculated field. Furthermore, the plant from the inoculated field
contained 8.4 kg N/ha more than the uninoculated field. Also, using algae as
fertilizer will improve the soils' water holding capacity which is an advantage to
crop yield (Alexopulos and Bold 1967).
5.4.3 Algae for energy
The fuel characteristics of dry algae (average heat content of 6 kcal/g) are
similar to those of medium-grade bituminous coal, and suitable for using as
energy source (Benemann et al. 1980). Algae can be used together with other
organic amendments to produce biogas from anaerobic digestion.
5.4.4 Algae as source of chemicals
A significant amount of lipids is present in algal cells (Table 5.12), which can be
used for many industrial purposes such as manufacturing of surfactants, grease,
textiles, food additives, cosmetics and pharmaceuticals. The lipids of micro
algae often contain large amount of neutral lipids, mainly as glycerides, and this
might serve as a source of glycerol (Aaronson et al. 1980).
Micro algae may also serve as a source of steroids. The concentration of
steroids in algae is variable but significant amount may be found in some algae.
Algae may also contain upto 0.2% of dry weight as carotenoids (Paoletti et al.
1976). Some medicinal products have been isolated from algae (Volesky et al.
1970).
5.4.5 Algae as a future life support technology
As shown in Figure 1.1 and Table 1.2, the increase in population growth and
decrease in arable land will require technologies of food or protein production
which are cost-effective and use less land area. The HRAP technology as
described in this chapter should be able to respond effectively to this need and
the algal cells can be used at least as fish and other animal feeds. The current
progress in space exploration should eventually lead to a possibility that human
beings can stay in space, on the Moon or Mars for a longer period of time and
the algal technology that produces O 2 and algal protein biomass is being
considered as a potential life-support technology.