Dual-phase phosphorus dynamics in Chlorella vulgaris : bridging r/K selection theory with wastewater bioremediation

ABSTRACT

Microalgae, particularly Chlorella vulgaris shows strong potential for phosphorus removal from wastewater, yet the underlying uptake and storage mechanisms remain unclear. This study investigated the dynamic phosphorus removal process in a gradient-loading photobioreactor using this species, aiming to reveal the transitional mechanisms and their ecological relevance. Results demonstrated a clear biphasic removal pattern. At low to moderate total phosphorus concentrations (3–12 mg/L), removal shifted from short-term physicochemical adsorption to long-term biochemical assimilation, consistent with an ecological transition from r- to K selection strategies. Under these conditions, phosphorus recovery efficiency reached 48–93%, and biomass phosphorus content increased to 3–11%, exceeding most reported values. Initially, removal was governed by electrostatic interactions and precipitation, with extracellular polymers acting as temporary storage; subsequently, intracellular polyphosphate accumulation became dominant. However, a critical threshold was identified at total phosphorus above 48 mg/L, beyond which metabolic stress–induced strategy collapse, cell rupture, and net phosphorus release, underscoring the limitations of excessive loading. These findings advance the understanding of microalgal adaptive responses to phosphorus stress and provide a load-based optimization framework for designing stable and efficient wastewater phosphorus recovery systems, with practical implications for managing influent fluctuations in treatment facilities.