Effects of depth and light availability on the growth of Spirulina maxima in urea used culture medium at outdoor culture

Abstract

The effect of depth and surface shadow on the growth, biomass production and biochemical composition of S. maxima was studied at outdoor mass culture at Chuuk, Federated States of Micronesia (FSM) where the climate is tropical with air temperature variation of 26 to 32？C temperature throughout the year. Culture was carried out in Fiberglass Reinforced Plastics (FRP) tanks in a medium consist of urea, soil extract, and cooking salt with lower concentration NaHCO3 and Na2CO3 than that of Zarrouk…s medium. The depth of 25 cm showed better growth of S. maxima than that of 30 and 35 cm depth, and the highest biomass production was at 25% surface shadow tanks having 25 cm depth, where the specific growth rate and biomass production were 0.35 d-1 and 2.05 g L-1, respectively. The FRP tanks having medium depth of 35 and 30 cm with 50% showed very strong ammonia smell and the cultures were died on 4 and 6th day when pH was above 8.80 and light intensity decreased to 450？105 Lux due to cloudy sky. Microscopic observation revealed that the average coils number in the trichome was 8.70 without contamination by other plankton in the highest biomass production culture condition. The protein, lipid, carbohydrate, water and ash content of S. maxima of best growth biomass was 56.59%, 0.94%, 14.42%, 5.03% and 23.02%, respectively on dry weight basis. The amino acid analysis of protein showed ten essential and eight non-essential amino acids. Among the essential amino acid, leucine (9.83%) was highest followed by arginine (6.86%), and in non-essential amino acid, glutamic acid was 15.08% followed by aspartic acid (9.83%). The minerals content, Na, K, Fe and Mg were 65.80, 24.26, 5.34 and 3.52 mg. (100g)-1, respectively. The study provided new data on the safety using of urea for the large scale production of S. maxima with low cost culture medium.