Potential of a local microalgal strain isolated from anaerobic digester effluents for nutrient removal

Anaerobic digestion effluents contain nitrogen and phosphorous which require reduction to accomplish the corresponding discharge legislation. Microalgae can be used as an alternative treatment to reach the required effluent quality. However, only robust and fast growing microalgae species are required in order to ensure stable and efficient nutrient removal under the conditions existing in wastewater treatment plants. Consequently, maintaining a stable microalgae community adapted to this environment becomes a key issue. In this work, a local microalgal strain was isolated from an anaerobic digester effluent (ADE). Microalgal growth was defined as the isolation criteria. The isolated microalgae were identified by molecular techniques as Chlorella sorokiniana (strain S12/S13/S16). Nutrient removal capacity from the ADE was assessed for the isolated strain by cultivation on ADE in repeated batch mode. Growth was limited by phosphorus, which reached removal efficiencies close to 100%. Under such conditions, biomass productivity and growth rate were barely enhanced with CO ₂ -enriched air not compensating the extra cost of CO ₂ addition. Finally, in order to close the process scheme, the methane potential of the isolated C. sorokiniana was assessed. The methane production capacity was 376 mL CH ₄  g ⁻¹ volatile solids, similar to values reported for other microalgae species. The novelty of this work lies in the isolation of a robust local microalgal strain that ensures a high nutrient removal capacity from ADE. The efficiency and stability of the nutrient removal process might be enhanced by isolation and controlled growth of local, robust, and also fast-growth microalgae species.