Evaluation of photobioreactor heat balance for predicting changes in culture medium temperature due to light irradiation

Abstract

Microalgal photosynthesis requires appropriate culture medium temperatures to achieve high photosynthetic performance and to maintain production of a high-quality biomass product. Enclosed systems, such as our conical, helical tubular photobioreactor (HTP), can accomplish high photosynthetic efficiency and the small amount of culture medium used by these systems means that the culture medium temperature may be effectively controlled. On the other hand, because a high ratio of surface area to culture medium volume leads to rapid heating under the illumination condition and substantial heat loss at night, maintaining a suitable culture medium temperature is necessary to achieve efficient, commercially practical biomass production. In order to predict changes in the culture medium temperature caused by changes in solar irradiance and ambient temperature, it is necessary to understand the heat balance within the photobioreactor. We therefore investigated the heat balance in three major parts (photostage, degasser, and helical heat exchanger) of our conical HTP, analyzed the time-dependent changes in medium temperature at various room temperatures and radiant energy inputs, and predicted changes in the culture medium temperature based on the characteristics of heat transfer among the three parts. Using this model, the predicted changes in culture medium temperature were very similar to the changes observed experimentally in the laboratory and under field conditions. This means that by calculating the time-dependent changes in the culture medium temperature, based on measurements of solar energy input and ambient temperature, we should be able to estimate the energy required to maintain the culture medium temperature within a range where photosynthetic performance of microalgae is high.

Past, Present and Future of Microalgae Cultivation Developments

“…In closed photobioreactors, the main challenge is being less economical than open ponds (Borowitzka 1996;Moheimani and McHenry 2013;Moheimani et al 2013c;Pulz and Scheibenbogen 1998). A number of researchers have endeavoured to overcome a number of the limitations in closed including: • reducing the light path (Borowitzka 1996;Janssen et al 2002;Miron et al 1999) • solving shear (turbulence) complexity (Barbosa et al 2003;Borowitzka 1996;Miron et al 2003) • reducing oxygen concentration (Acién Fernández et al 2001;Kim and Lee 2001;Rubio et al 1999;Weissman et al 1988), and • temperature control system (Becker 1994;Borowitzka 1996;Carlozzi and Sacchi 2001;Morita et al 2001;Rubio et al 1999;Zhang et al 1999). …”

Opportunities for renewable bioenergy using microorganisms

“…They keep down the capital costs, but offer limited control over the growth conditions, evaporative water loss, and invasion of non-desired species. Enclosed photobioreactor systems (e.g., Borowitzka, 1999;Christi, 2007;Hai et al, 2000;Morita et al, 2001;Pulz, 2001) can overcome the limitations of the open ponds, but incur increased capital costs. Furthermore, enclosed systems vary widely, ranging from transparent bags exposed to the sun to highly sophisticated photobioreactor systems that employ the latest technology for monitoring, control, light collection, water management, and biomass harvesting.…”

Light Regime Characterization in an Airlift Photobioreactor for Production of Microalgae with High Starch Content

“…The original growth medium based on the elementary composition of algal biomass had the following initial composition (mg l − 3 in distilled water; the initial pH was adjusted to 7.0 by 0.1 M NaOH.…”

“…Microalgae have a greater capacity for photosynthesis than higher plants, which raises the possibility that they could effectively utilize the CO 2 in stack gases from thermal power plants to synthesize a variety of valuable substances like starch or oil [2,3].…”