Photosynthetic performance and nutrient removal from anaerobically digested effluents by microalgal biofilms

Selecting microalgal species with efficient nutrient uptake capabilities and employing an effective cultivation system are critical to successful AD effluent reclamation. While Scenedesmus sp. MUR 272 and Chlorella sp. MUR 269 have shown efficiency in suspension-based ADFE treatment, biofilm-based cultivation presents a promising, cost-efficient alternative for ADFE valorization. Our study investigates the feasibility of cultivating these strains in biofilm to treat ADFE, using the modified F/2 medium as a control. Growth monitoring and Chlorophyll a (ChlF a) fluorescence measurement assessed algal performance in the biofilm. Biomass yield ranked as follows: Chlorella sp. ADFE>Scenedesmus sp. ADFE>Scenedesmus sp. MF/2>Chlorella sp. MF/2. Both species demonstrated significantly higher biomass productivity in ADFE than in MF/2. ChlF a fluorescence data revealed that Scenedesmus maintained a relatively more stable photosynthetic performance than Chlorella as the culture progressed. Both algal species exhibited a similar fluorescence induction curve in both ADFE and modified F/2. While the intensity of the fluorescence of Chlorella increased as the culture progressed, that of Scenedesmus decreased till day 10, especially at the J and I step, suggesting the presence of stress factor in Chlorella culture. Efficient nutrient removal performance was achieved with 87–100 % for ammoniacal nitrogen (NNH3) and 73–85 % for phosphate. More protein and carbohydrates were produced on day 4 than on day 10 in both algal species, with Chlorella showing higher productivity of both metabolites than Scenedesmus. These microalgal species' efficient nutrient uptake capabilities and protein yield in the biofilm system hold promise for effective and cost-efficient valorization of AD effluents.