Effect of algae pigmentation on photobioreactor productivity and scale-up: A light transfer perspective

This paper reports a numerical study coupling light transfer with photosynthetic rate models to determine the size and microorganism concentration of photobioreactors based on the pigmentation of algae to achieve maximum productivity. The wild strain Chlamydomonas reinhardtii and its transformant tla1 with 63% lower pigmentation are used as exemplary algae. First, empirical models of the specific photosynthetic rates were obtained from experimental data as a function of local irradiance using inverse methods. Then, these models were coupled with the radiative transfer equation (RTE) to predict both the local and total photosynthetic rates in a planar photobioreactor (PBR). The optical thickness was identified as the proper scaling parameter. The results indicated that under full sunlight corresponding to about 400 W/m2 photosynthetically active irradiation, enhancement of PBR productivity up to 30% was possible with tla1. Moreover, under similar irradiation, optical thicknesses above 169 and 275 for the wild strain and tla1, respectively, did not further enhance PBR productivity. Based on these results guidelines are provided for maximizing PBR productivity from a light transport perspective.

► Enhancing photobioreactor productivity with the less pigmented algae tla1 is investigated. ► Enhanced light penetration is identified to be dominant over reducing photoinhibition. ► Optical thickness is identified as an appropriate scaling parameter for PBR design and analysis. ► No productivity enhancement is expected using tla1 for irradiances less than 50 W/m2 in PAR. ► Under full sunlight, up to 30% increase in productivity can be achieved using tla1.