Intensive Microalgal Cultivation and Tertiary Phosphorus Recovery from Wastewaters via the EcoRecover Process

Area of Science:

• Environmental Engineering
• Microalgal Biotechnology
• Wastewater Treatment

Background:

• Mixed community microalgal systems offer potential for nutrient recovery and renewable carbon feedstock production.
• Optimization and control require a deeper understanding of their performance characteristics.
• Tertiary phosphorus removal is a critical step in advanced wastewater treatment.

Purpose of the Study:

• To characterize the performance of a full-scale microalgal wastewater treatment system (Clearas EcoRecover) for tertiary phosphorus removal.
• To investigate the mechanisms of phosphorus uptake and accumulation in a mixed algal community.
• To identify key operational parameters for stable and efficient phosphorus removal.

Main Methods:

• Continuous online monitoring and long-term on-site monitoring of a 568 m³·day⁻¹ Clearas EcoRecover system.
• On-site batch experiments to assess phosphorus uptake dynamics.
• Analysis of microbial community composition and key water quality parameters (pH, alkalinity, dissolved oxygen).

Main Results:

• The system achieved a stable effluent total phosphorus concentration of 0.03 ± 0.03 mg-P·L⁻¹ over a 3-month winter period.
• Carbohydrate storage in photobioreactors was demonstrated to be crucial for supporting phosphorus uptake in dark conditions.
• Polyphosphate accumulation was observed in the mixed algal communities, indicating efficient phosphorus recovery.
• Core microbial taxa included *Chlorella spp.*, *Scenedesmus spp.*, and *Monoraphidium spp.*.
• Stable performance was correlated with near-neutral pH, sufficient alkalinity, and a diel dissolved oxygen rhythm.

Conclusions:

• Mixed microalgal systems are effective for tertiary phosphorus removal and recovery as biomass in operational wastewater treatment facilities.
• Understanding algal physiology, particularly carbohydrate storage, is vital for optimizing phosphorus uptake.
• Key operational parameters must be maintained for consistent system performance and high-quality effluent.