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Microalgae starvation for enhanced phosphorus uptake from municipal wastewater

Aigars Lavrinovičs, Linda Mežule, Tālis Juhna
Algal research 2020 v.52 pp. 102090
Chlorella, Desmodesmus, Tetradesmus, ambient temperature, biomass, carbon dioxide, cells, correlation, dissolved inorganic nitrogen, inorganic phosphorus, microalgae, municipal wastewater, pH, research, starvation, strains, wastewater treatment
Three microalgal species, Desmodesmus communis, Tetradesmus obliquus and Chlorella protothecoides were studied for enhanced phosphorus removal from municipal wastewater. Microalgae were first exposed to phosphorus deficit conditions for 7 and 14 days and then inoculated in filtered primary or secondary wastewater from a small municipal wastewater treatment plant at ambient temperature and CO₂ concentration. D. communis and T. obliquus strains showed higher biomass growth rates in secondary wastewater after 7-day starvation period, while C. protothecoides grew better in the same effluent without starvation. All strains were able to achieve nearly complete (>99.9%) removal of dissolved inorganic phosphorus (DIP). Moreover, D. communis and T. obliquus showed ~89% DIP reduction within 24 h after 7-day phosphorus starvation. Dissolved inorganic nitrogen removal for all algal strains did not exceed 50% for any of the treatments. All three strains were able to store excess phosphorus within their cells as polyphosphate and the highest Poly-P content was observed in cultures grown in primary wastewater. Poly-P concentration in C. protothecoides reached 250 μg mg⁻¹. At the same time no correlation between Poly-P and P removal was observed. The efficiency of nutrient (P) removal from municipal wastewater to ultra-low levels (<0.1 mg L⁻¹) is closely linked to algae starvation and auxiliary factors, like environmental pH and N/P ratio.