Algae-facilitated chemical phosphorus removal during high-density Chlorella emersonii cultivation in a membrane bioreactor

• An algae-based membrane bioreactor was evaluated for wastewater treatment and nutrient removal.
• The extracellular P accounted for >90% of the total phosphorus in the algae biomass.
• Algae-induced P precipitation is key to P removal in high-density algae cultivation.
• The P enriched algal biosolids had excellent settling properties.
• Low tendency for membrane fouling due to the low algal EPS production.

An algae-based membrane bioreactor (A-MBR) was evaluated for high-density algae cultivation and phosphorus (P) removal. The A-MBR was seeded with Chlorella emersonii and operated at a hydraulic retention time of 1 day with minimal biomass wastage for about 150 days. The algae concentration increased from initially 385 mg/L (or 315 mg biomass COD/L) to a final of 4840 mg/L (or 1664 mg COD/L), yielding an average solids (algae biomass + minerals) production rate of 32.5 g m−3 d−1 or 6.2 g m−2 d−1. The A-MBR was able to remove 66 ± 9% of the total P from the water while the algal biomass had an average of 7.5 ± 0.2% extracellular P and 0.4% of intracellular P. The results suggest that algae-induced phosphate precipitation by algae is key to P removal and high-density algae cultivation produces P-rich algal biomass with excellent settling properties.

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