222 Organic waste recycling: technology and management
5.1 OBJECTIVES, BENEFITS AND LIMITATIONS
With respect to algal mass culture in wastewater, efforts have been directed
towards single cell protein production for potential human and animal
consumption. The desirable properties of algal single cell protein are:
- High growth rate
- Resistance to environmental fluctuations
- High nutritive value
- High protein content
- Ability to grow in wastewater
The production of algal biomass from wastewater has the following
objectives and benefits:
5.1.1 Wastewater treatment and nutrient recycling
The biological reactions occurring in the algal ponds reduce the organic content
and nutrients of the wastewater by bacterial decomposition, and convert them
into algal biomass by algal photosynthesis. Algal cells have high protein value,
and subsequent harvesting of algae for human and animal consumption will be
the financial incentive to wastewater treatment. The average production of algae
is reported as 70 tons/(ha-yr) or 35 tons/(ha-yr) algal protein; comparing with
the productivity of conventional crops, wheat 3.0 (360 kg protein), rice 5.0 (600
kg protein) and potato 40 (800 kg protein) tons/(ha-yr) (Becker 1981).
Almost all the organic wastes such as municipal wastewater, agricultural and
animal wastes can be treated by the algal systems, resulting in considerable algal
biomass yields.
5.1.2 Bioconversion of solar energy
Solar energy is the primary source of energy for all life. This energy is utilized
by phytoplankton during photosynthesis and synthesis of new cell occurs. Algae
are phytoplankton and they are the primary producers in the food chain with
high productivity. Therefore algal production will be the efficient method of
conversion of solar energy.
5.1.3 Pathogen destruction
Wastewater usually contains pathogens that are harmful to human. Therefore
pathogen destruction with waste stabilization is advantageous in waste recycling
process. Some magnitude of pathogen destruction occurs in algal ponds due to