Optimizing algal biomass production in an outdoor pond: a simulation model

A deterministic simulation model was developed to predict production rates of the marine prymnesiophyte Isochrysis galbana in an outdoor algal mass culture system. The model consists of photoadapation, gross photosynthesis and respiration sections. Actual physiological and biophysical laboratory data, obtained from steady state cultures grown under a wide range of irradiance levels, were used in calculating productivity. The resulting values were used to assess optimal operational parameters to maximize algal biomass production. The model predicted a yearly averaged production rate of 9.7 g C m^-2d^-1, which compared well with field data reported in the literature. The model evaluated the effect of pond depth and chlorophyll concentration on potential production rate in various seasons. The model predicted that a yearly averaged chlorophyll areal density of 0.65 g m^-2 will yield the maximal production rate. Chlorophyll areal density should be seasonally adjusted to give maximal production. This adjustment could be done either by changing pond depth or chlorophyll concentration. The model predicted that under optimal operational conditions, the diurnal respiration losses averaged 35% of gross photosynthesis. The calculated growth rate for maximal productivity ranged between 0.15 and 0.24 d^-1, suggesting an optimal hydraulic retention time of 6.7 and 4.2 d for various seasons.