Light energy effect on Spirulina platensis growth rate

The effects of light intensity and initial concentration of Spirulina platensis on growth were investigated. Light intensity levels were varied between 2 to 8 klux in steps of 2 klux. Light was supplied by 40-Watt fluorescent tubes. Initial Spirulina platensis concentrations investigated were 100, 200, 400, and 600 mg/L. The medium used for Spirulina platensis growth was a modified Zarrouk medium. Light radiation levels were controlled by exposing algae to light within specific area on a surface with a (1 mm) depth of culture. Also, by controlling the velocity flowing on the glass plate exposed to the light source, calculations of light radiation input to the culture were possible. The biological clock of Spirulina, in a 400 mg/L culture under 4 klux of light, was investigated to determine the appropriate time length for each trial to be conducted in the main experiment. There was a distinct dial pattern of growth between the hours of 0800 and 1100. Results showed that the first 3 hours of growth represented a maximum growth of the culture. Since Spirulina used in the main experiment were taken from a nutrient and light energy deficient culture, starved culture, verification of the effect of using the starved culture on the biological clock of growth was needed. Therefore, three tests were conducted in duplication of 2, 3-hour time periods each, starting at the hours of 1100, 1530, and 1900, which represented the low algae production periods of the biological growth clock. Results showed that the time of day the tests were conducted had no effect on the 3-hour growth results, where initial Spirulina concentrations were supplied from nutrient and light energy deficient stock culture. Statistical analysis showed no significant differences between treatments at the low algae production times at a=O.Ol. Therefore, data for the main experiment were collected without regard of the time of day. For the main study, each treatment level was allowed to grow for 3 hours. Results proved that within the ranges of light intensity and algae concentration levels tested, an algae concentration of 400 mg/L provided the maximum growth conditions under any of the light intensity levels examined. Results were based on the net increase in algae concentration for the 3-hour time periods. Also, analysis of variance test for the data showed significant differences among treatment levels at the a=O.Ol level.