EVALUATION OF PHOTOSYNTHETIC EFFICIENCY IN MICROALGAL CULTURES USING AVERAGED IRRADIANCE

The growth yield of the PUFA-producing marine microalga Isochrysis gal bana grown in Eight-limited continuous operation was measured under a wide variety of conditions of incident irradiance (I-o) and dilution r ates (D). The experiments were conducted under laboratory conditions a t 20 degrees C with continuous light. D ranged from 0.0024-0.0410 h(-1 ) at three values of I-o (820; 1,620; and 3,270 mu E m(-2) s(-1)) clos e to those found in outdoor cultures. A maximum efficiency of psi(max) = 0.616 g E-1 was obtained at I-o = 820 mu E m(-2) s(-1) and D = 0.03 0 h(-1), and the maximum capacity of the biomass to metabolize light w as found to be 13.1 mu E g(-1) s(-1). Above this value, a significant drop in system efficiency was observed. A new approach based on averag ed irradiance is used to assess the photon flux absorbed by the biomas s. The biomass productivity to be expected in an outdoor tubular photo bioreactor growing I. galbana was predicted from efficiency data obtai ned in laboratory cultures and was found to be in agreement with the a ctual value. (C) 1997 Elsevier Science Inc.