Biological utilization of phosphorus-containing sediment waters using green microalgae: Efficiency, mechanisms, and optimization

Abstract

Phosphorus pollution in sediment-derived waters poses a critical environmental challenge, driving eutrophication in freshwater and coastal ecosystems. Conventional physicochemical removal methods are costly and generate secondary pollutants. This study investigates the biological utilization of phosphorus from sediment-laden drainage water using three green microalgal species – Chlorella vulgaris , Scenedesmus quadricauda , and Desmodesmus communis – and their mixed-culture consortium under controlled photobioreactor conditions. Batch experiments were conducted over 14 days at 25 ± 1 °C with varying light intensities (50–200 µmol photons m⁻²s⁻¹) and initial pH levels (6.5–8.5), following a staged design in which species were first compared under a common reference condition and C. vulgaris was then used as a representative strain for detailed light-and pH-optimization. Water samples were characterized for total phosphorus (TP), orthophosphate (PO₄³⁻-P), total nitrogen (TN), chemical oxygen demand (COD), and biomass productivity. The mixed culture ( C. vulgaris : S. quadricauda = 1:1) achieved the highest TP removal efficiency of 92.8 ± 1.5% and PO₄³⁻-P removal of 95.3 ± 1.2% at pH 8.0 and 200 µmol m⁻²s⁻¹ illumination, with a maximum biomass productivity of 2.01 ± 0.09 g L⁻¹. Phosphorus removal occurred primarily through assimilatory uptake and luxury polyphosphate accumulation, supplemented by a smaller, pH-dependent chemical co-precipitation pathway inferred from mass-balance differences and not directly confirmed mineralogically. Kinetic analysis revealed first-order removal rate constants of 0.18–0.22 d⁻¹. The results indicate that microalgae-based biotreatment is a promising alternative for remediating phosphorus-contaminated sediment waters, with the resulting phosphorus-enriched biomass representing a candidate feedstock for biofertilizer applications.