Effect of light intensity on Chlorella sp. biofilm growth on anaerobically digested food effluents (ADFE)

Optimizing light conditions in any culture design for effluent treatment is crucial for maximizing microalgae growth and nutrient uptake. We investigated the impact of low (53 ± 1 μmol m^-2 s^-1), medium (208 ± 12 μmol m^-2 s^-1), and high (518 ± 22 μmol m^-2 s^-1) light intensities on the diffused biofilm-based growth of Chlorella sp. for treating anaerobically digested food effluent (ADFE). The alga grew well across all treatments, irrespective of light intensity. However, biomass yields, and productivity positively correlated with light intensity, with the highest biomass yield (120 g m^-2) and productivity (11.6 g m^-2 d^-1) occurring at high light intensity. Notably, specific growth rates peaked uniformly on day 2 across all treatments, indicating an initial surge in growth. A relatively stable photosynthetic performance occurred under medium light treatment, while stress evidence was noticed particularly after day 4 at high and low light treatments, with higher magnitude seen under low light treatments. Total ammonia nitrogen (TAN) and phosphate removal efficiencies increased with light intensities, reaching 100 % removal at high light after 10 days. Intriguingly, there was a notable enhancement in chemical oxygen demand (COD) removal under low light conditions, being 2.9- and 1.64-fold higher compared to medium and high light intensities, respectively. Despite the superior performance of Chlorella sp. biofilm under high-light conditions in biomass yield and uptake of nutrients, the low-light treatment also achieved remarkable results, indicating that this biofilm design offers enhanced exposure to light. Therefore, this biofilm configuration presents an enticing opportunity for treating ADFE at lower light intensities, potentially minimizing energy consumption while maximizing profitability.