Microalgae harvesting from wastewater by pH modulation and flotation: Assessing and optimizing operational...

Area of Science:

• Environmental Biotechnology
• Water Treatment
• Microalgae Cultivation

Background:

• Microalgae harvesting is a major challenge for large-scale production of valuable microalgal products.
• Dissolved air flotation (DAF) is a promising, yet under-explored, harvesting technique compared to sedimentation.
• Wastewater cultivation of microalgae offers a sustainable approach but requires efficient biomass recovery and effluent treatment.

Purpose of the Study:

• To optimize operational parameters for pH modulation and dissolved air flotation (DAF) for harvesting Chlorella sorokiniana.
• To assess the reproducibility and resilience of the optimized harvesting method against wastewater variability.
• To evaluate the impact of microalgae harvesting on the final wastewater quality.

Main Methods:

• Optimization of coagulation parameters (pH, velocity gradient, mixing time) and flotation parameter (recirculation rate) using the one-factor-at-a-time method.
• Cultivation of Chlorella sorokiniana in wastewater.
• Application of pH modulation followed by dissolved air flotation (DAF) for microalgae harvesting.

Main Results:

• Optimal parameters identified: velocity gradient of 500 s⁻¹, 30s mixing time, pH 12, and 20% recirculation rate.
• High Chlorella sorokiniana removal efficiencies achieved (96.5-97.9%).
• Significant improvements in wastewater quality: 88.6-95.1% removal of total Kjeldahl nitrogen, 91.8-98.3% removal of total phosphorus, and 80.5-86.8% removal of chemical oxygen demand.

Conclusions:

• pH modulation combined with DAF is an effective and efficient process for both microalgae harvesting and wastewater treatment.
• The optimized harvesting method demonstrates resilience and applicability for large-scale microalgae production.
• This study provides practical guidelines for operational optimization in microalgae harvesting from wastewater.