Photobioreactor chemostat operation

Microalgae can also be grown continuously meaning that the microalgal culture is continuously harvested and the liquid volume removed is continuously replaced with fresh water with nutrients. In the case of chemostat operation the dilution rate is fixed. Assuming a constant photon flux density a steady state will be reached where the biomass concentration does not change anymore and is constant. The influent, water with nutrients, usually does not contain any microalgae. Furthermore, the liquid voltune is usually maintained constant, so Tm = Tout=fr- Finally, it wiU be assumed that the liquid inside the photobioreactor is perfectly mixed, so C om = Cx. Then the biomass balance over the photobioreactor can be simplified as follows ... 

Under outdoor conditions under day/night cycles biomass accumulation inside the photobioreactor cannot be neglected. Especially in case of chemostat operation considerable changes in biomass concentration will occur. Even in a turbidostat in the ri ht biomass concentrations will decrease because of respiration. The biomass balance then must be written as follows ... 

This study demonstrates the principal possibility of hydrogen production in an outdoor photobioreactor (PhBR) incorporating a cyanobacterial mutant of Anabaena variabilis (PK84) under aerobic conditions. A computer-controlled helical tubular PhBR was operated over 4 summer months. A maximum rate of 80 mL H2 per hr per reactor volume (4.35 L) was obtained on a bright day (400 W m 2) from a batch culture. Also the culture was grown in chemostat mode at dilution rate D of 0.02 h 1. The maximum efficiency of conversion of light to chemical energy of H2 in the PhBR was 0.33% and 0.14% on a cloudy and a sunny day, respectively. 

Photobioreactors usually are operated according to a chemostat mode (constant dilution) or turbidostat mode (constant turbidity) of operation. Details will be explained later in this chapter but below the hiomass balance over a microalgal cultivation system is aheady presented ... 

Microalgae can be grown batchwise in photobioreactors. In case biomass concentrations become too high the culture is diluted, and biomass is harvested, after which growth is allowed to continue again. Microalgae production systems can also be operated in a continuous manner based on a chemostat or turbidostat mode of operation. Flere these three different... 

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