Sewage-grown micro-algae

One of the indirect methods for the utilization of animal (or human) excrete as feed is the cultivation of micro-algae on waste water or sewage. The process is aimed primarily at sewage purification and water reclamation, but the resulting algal biomass is of considerable interest as feed. This material, after harvesting, concentration, and drum drying, contains 45 to 55 per cent protein, It can replace half of the soybean meal in commercial broiler rations with no deleterious effect on growth.

In vivo experiments with chicks showed that about 80 per cent of algal protein is absorbable. The metabolizable energy content of the material is 2,000 to 2,800 kcal/kg. In addition to their value as a source of protein and calories, algae also contain carotenoids that enhance the desirable pigmentation of carcass skin and egg yolk. Although the technology is not sophisticated, growing algae requires a somewhat large-scale operation to be profitable. Algae grown on municipal sewage may contain high levels of heavy metals, particularly if the sewage contains industrial waste-water. However, these heavy metals seem to be unabsorbed by chicks and do not appear in the composition of edible tissues and bones. In the light of the results of four years of research in our laboratories, algae grown on sewage seem to be safe and valuable as a feed ingredient for poultry and fish.