Timing is everything: optimizing crop yield for Thalassiosira pseudonana (Bacillariophyceae) with semi-continuous culture.

There is relatively little choice in cultivation methods for growing algae outdoors, either in open pond systems or closed photobioreactors-as batch, continuous, or semi-continuous culture. Algal batch culture grown in a nutrient replete environment with adequate sunlight will become self-shaded with sufficient cell density and enter a stage in the growth dynamic known as the 'phase of linear growth.' It is during this phase of linear growth that primary production is at maximum and that the highest biomass is harvested. The inherent problem with batch culture is that the exponential (and possibly lag) phases necessary to achieve densities required prior to the phase of linear growth consume time and waste surface area, and thereby make this an inefficient method to grow algae. Semi-continuous culture can be forced into shade-limiting conditions by reducing growth rate from maximum through dilution, whereby phases of lag and exponential growth are skipped, and culture growth is put into a state similar to a perpetual phase of linear growth with an appropriate culture harvest/dilution cycle. Importantly, semi-continuous culture can increase net growth efficiency over batch culture when compared by shade-limited growth rate. However, scientific study and theory covering shade-limited algal growth under semi-continuous culture conditions are nearly non-existent, which currently makes its application to phycological technologies impractical through 'hit and miss' strategies. This laboratory study compares shade-limited growth dynamics for batch and semi-continuous cultures of Thalassiosira pseudonana (small-sized, marine diatom). Theory for optimizing production of mass algal culture with semi-continuous culture technique through cycle period and harvest volume is developed, and guidelines to practical industrial applications are provided. [ABSTRACT FROM AUTHOR]