Enhanced biomass/biofuel production and nutrient removal in an algal biofilm airlift photobioreactor

The production of algal biofuel has received increasing attention in recent years but is still not economically feasible due to a lack of reliable and cost-effective microalgal cultivation systems. In this study, a unique algal biofilm airlift photobioreactor (ABA-PBR) was developed for attached growth of the alga Chlorella vulgaris on a culture medium consisting of treated sewage. When the ABA-PBR is aerated, solid carriers suspended in the reactor are dispersed throughout the reactor via fluid circulation. A portion of the algal cells in the reactor are able to attach to and grow on the carriers. Prior to ABA-PBR experiments, batch adsorption experiments were performed to choose the best solid carrier for the ABA-PBR. The carriers were named C-1, C-2 and C-3 and were made of fiber, plastic and terylene respectively. The highest microalgal adsorption capacity was observed for Carrier C-1, which exhibited a biomass adsorption capacity of 32.9 mg (g carrier)− 1. Carrier C-1 was therefore added to the ABA-PBR for algal cell attachment. Compared to a conventional photobioreactor (C-PBR) without solid carriers, the ABA-PBR achieved a higher volumetric biomass productivity (15.93 mg L− 1 d− 1), and a higher algal lipid productivity (4.09 mg L− 1 d− 1), as the solid carriers in the ABA-PBR facilitate the development of the algal biofilm system in the reactor. An aerial biomass productivity of 0.82 g m− 2 d− 1 was also achieved with the developed algal biofilm in the ABA-PBR. Furthermore, improved nutrient removal rates (1.00 and 0.20 mg L− 1 d− 1 for N and P, respectively) were also achieved in ABA-PBR due to the higher algal biomass productivity of the reactor.