Reduction of water and energy requirement of algae cultivation using an algae biofilm photobioreactor.
The feasibility of attached culture Chlorella vulgaris in a porous substratum biofilm reactor (PSBR) for simultaneous wastewater treatment and biofuel production was investigated. The characteristics, including algal biofilm growth, lipid yield, nutrient removal, and energy efficiency of the outdoor cultures, were investigated under the influence of both inoculum densities and the percent submerged area. A maximum biofilm productivity of 57.87 g m−2 d−1 with 81.9 % adhesion was achieved under optimal conditions (inoculum density of 18 g m−2 and the percent submerged area of 5.7 %). The lipid content and lipid yield were 38.56 % and 27.25 g m−2 d−1, respectively. Meanwhile, the algae removed 99.95 % ammonia, 96.05 % total nitrogen (TN), and 99.83 % total phosphorus (TP). Further, the energy life cycle for the PSBR was analyzed. The biomass productivity per unit irradiance was up to 4.6 g MJ−1 (photosynthetic efficiency of 10.65 %). The PSBR was considered to be economically feasible due to the net energy ratio of 1.3 (>1).