Under the aegis of the DST’s All India Coordinated project on Algae, NBRI had developed a soft technology for Spirulina production in sewage. Without being a health hazard, total use of sewage is envisaged for production of algal proteins (as animal feed), fish-culture and for irrigation water in an integrated pilot plant system. After extensive bench and field experiments, it has been possible to adapt Spirulina to raw and settled sewage, using sodium bicarbonate as a carbon source as also to maintain a high pH, required for satisfactory growth of algae. A system, therefore, of raw sewage, fortified with sodium bicarbanate (9g/l) and sodium nitrate (1.0g/l), has been developed which works very well and the alga grows profusely, without contamination. The major steps in the cultivation of S. platensis are preparation of inoculum, mass outdoor cultivation in high-rate oxidation ponds, harvesting and drying. The algal culture in sewage is to be supplied with optimum concentrations of bicarbonate and nitrogen sources. Agitation of the pond liquid is also necessary to provide uniform sunlight and also to prevent anaerobic conditions in the ponds. Under optimum conditions, the alga is ready for harvesting 10-15 days after the inoculum is introduced in the pond, and can be filtered by using polyester cloth. The filterate is cycled back into the ponds. The algal slurry is washed with water to remove excess bicarbonate before it is spread on thin plastic sheets and sun dried. The dried algal powder can be used as such as an ingredient of poultry and livestock feed. The average yield of Spirulina is 6.3-9.7 g per square metre, per day on dry weight basis. The production technology of Spirulina platensis has been implemented in an indigenously designed pilot plant, having an anticipated capacity for producing one metric ton of the algal powder per year. From the environmental point of view, the utilization of sewage to grow Spirulina has two advantages – production of low cost algal protein for animal feed and the reclamation of sewage.
