Physiology

Abstract

The Aquatic fern Azolla was used to treat waste water. Because of the capability of N fixation by Azolla, the efficient removal of phosphorus would be expected even after N is consumed. Azolla in outdoor batch cultures actively absorbed nutrients from the secondary treated effluent from May to October. The best growth with 2.5 days doubling time and the highest nutrient absorption were observed when tne P level was higher than the N level. The absorption capacity of Azolla was lower for nitrogen and higher for P than those of any other aquatic plants so far reported.

Subsequent analysis of chemical composition of Azolla suggested that it would be a good biomass source of green manure and animal feed. Although the test diet, 20% dried Azolla, gave a poorer weight gain in male rats than commercial diet, in female the same effect of both diets was observed. No abnormal symptoms were found in 5 organs and in the blood examinations in rats fed with Azolla diet. In a feeding experiment with Tilapia nilotica, the diet containing dried Azolla as 16.6% of the total weight showed the same effects on percent weight gain and feed efficiency when compared with the control diet which included casein as a protein source. However, both effects of Azolla on Tilapia declined with increasing rate of Azolla content in tne diets.

Key words:

• Azolla
• waste water
• nutrient absorption
• biomass