Optimization of Tubular Microalgal Photobioreactors with Spiral Ribs under Single-Sided and Double-Sided Illuminations

Microalgae can be raw materials for the production of clean energy and have great potential for development. The design of the microalgal photobioreactor (PBR) affects the mixing of the algal suspension and the utilization efficiency of the light energy, thereby affecting the high-efficiency cultivation of the microalgae. In this study, a spiral rib structure was introduced into a tubular microalgal PBR to improve the mixing performance and the light utilization efficiency. The number of spiral ribs, the inclination angle, and the velocity of the algal suspension were optimized for single-sided and double-sided parallel light illuminations with the same total incident light intensity. Next, the optimization results under the two illumination modes were compared. The results showed that the double-sided illumination did not increase the average light/dark (L/D) cycle frequency of the microalgae particles, but it reduced the efficiency of the L/D cycle enhancement. This outcome was analyzed from the point of view of the relative position between the L/D boundary and the vortex in the flow field. Finally, a method to increase the average L/D cycle frequency was proposed and validated. In this method, the relative position between the L/D boundary and the vortex was adjusted so that the L/D boundary passed through the central region of the vortex. This method can also be applied to the design of other types of PBRs to increase the average L/D cycle frequency.

EFFECT OF CHLORELLA AS A BIOFERTILIZER ON GERMINATION OF WHEAT AND BARLEY GRAINS

Most of the agriculture sectors have been dependent heavily on inorganic chemical-based fertilizers, which are harmful for both human health and environment. The utilization of beneficial microbes as a biofertilizer has become major concern in industrial agriculture for their potential role in food safety and sustainable crop production. In this study, we examined the effect of Chlorella on germination of barley and wheat grains. Seeds were germinated in culture medium containing microalga (Chlorella sp. 56) and grown for 3, 6, 9 and 12 days in order to study its effect on growth parameters. In conclusion, Chlorella suspension increased the seed growth compared to those of control (sterilized culture medium) of seed germination. The best treatments were 0.06 g/L and 0.23 g/L of algal suspension for the root and shoot lengths of barley and wheat seeds, respectively.