Biofilm reactors
A recent review on photobioreactors for hydrogen gas production compared various photobioreactor systems developed by different research groups, each using different mixing and lighting mechanisms, and operating with one of four possible microorganisms (Adessi and De Philippis 2014). The review compared the working volumes, hydrogen gas production rates, and light conversion efficiencies for each system, highlighting the trade-off between photobioreactor size and efficiency.
Of the various photobioreactors investigated, one system, which uses packed glass beads to form a biofilm and is used for the production of hydrogen gas with the bacterium Rhodopseudomonas palustris (Tian, Liao et al. 2010). This photobioreactor has a working volume of 1.2 litres, and a light-conversion efficiency of 56% when light of 590 nm wavelength is applied to the bacteria. Whilst being a relatively high-performing system in terms of working volume and efficiency (relative to comparable photobioreactor designs), this photobioreactor is also amenable to laboratory-scale production, relying primarily on standard laboratory equipment, with an adjustable setup. Furthermore, the authors have demonstrated the use of this photobioreactor with LEDs of three different wavelengths, including blue light, making it readily applicable to our blue-light-inducible NAD biosynthesis system.
In order to assess the potential for this photobioreactor system to be applied to the biosynthesis of NAD using blue light on an industrial scale, we would need to measure the rate of NAD production, the light conversion efficiency, and the necessary power input of the system. Only then could we provide an analysis as to the efficiency and applicability of this system for NAD biosynthesis, and develop potential improvements to the photobioreactor design. However, the successful application of this system for the production of hydrogen gas and the relatively simple and inexpensive design provide a promising starting point for the development of an industrial-scale NAD biosynthesis system.
