Cultivation options for indoor and outdoor growth of Chaetoceros gracilis with airlift photobioreactors

Various configurations and modes of airlift photobioreactors were examined in the cultivation of Chaetoceros gracilis. Internal loop and external loop airlifts were cultivated in a batch mode in a controlled indoor environment. The external loop system provided a better performance than the internal loop system due to better light exposure. A continuous operation was conducted in an internal loop airlift photobioreactors-inseries. This was designed to minimise the effect of light blocking due to overgrown cells as the high-density culture was, in this configuration, only limited to the last airlift column in the series. Outdoor large-scale operation was conducted in a flat-panel airlift photobioreactor. Due to uneven light availability, the outdoor culture could not perform as well as the indoor one in terms of growth rate. Among the four systems investigated, the continuous culture in airlift photobioreactors-in-series provided the best performance with the highest cell density of 12.12 × 10 cells mL. Cost analysis based on the maximum number of reactors that can be installed in one square metre indicates that the indoor system requires lowest operating cost per unit cultivation area, whereas the outdoor system provides highest profit as a result of the inherited large productivity.