Welcome to the Glass Age

71 excessive discharge of nitrogen and phosphorus that cause eutrophication. A suitable microalga can also produce bioelectricity in microbial fuel cells, and hydrogen for use as a pollution-free fuel. For an efficient production of microalgae for any of these applications with low probability of contamination, photobioreactors such as seen in Figure 4.8 are required. These closed systems offer desired control of the algae production process. Ideally, a photobioreactor system should allow control of: light penetration and distribution within the culture medium; CO 2 loading level; mixing and gas transfer; management of oxygen generated as a byproduct of photosynthesis process; temperature; pH; supply of nutrients; and hydrodynamic residence time. The material requirements for the containment of microalgae within a photobioreactor system are to: (a) be chemically stable so that it does not corrode in salt water and can be cleaned and disinfected with commercial chemicals; (b) have a smooth surface and regular shape for uniform flow of medium to prevent biofilm formation; and (c) exhibit high transparency to Figure 4.8. A photobioreactor made by Varicon Aqua for microalgae production; tubes are made of borosilicate glass. Source: Courtesy of Akihiko Kanamoto, OP Bio Factory Co., Ltd, & Varicon Aqua.