Pilot-scale non-sterile mixotrophic cultivation of Galdieria sulphuraria for high-efficient removal of ammonium with enhancing high-protein biomass production from industrial effluent

Abstract

A complete demonstration system was established, covering non-sterile mixotrophic cultivation of G. sulphuraria for wastewater treatment from laboratory (50-L) to pilot scale (500–10,000 L) over 355 h, with spray-dried high-protein biomass production. The maximum removal rates of NH₄⁺-N (2,170.40 mg/L/d) and PO₄^3--P (700.40 mg/L/d) were achieved, alongside the highest productivity of biomass (30.00 g/L/d) and protein (13.51 g/L/d) in batch 2 of 10,000-L photo-fermenter. The significant decline in microbial abundance following non-sterile cultures mitigates environmental and health risks of the treated effluent. The final spray-dried powder is regarded as an ideal protein source for feed, characterized by high protein and very low levels of microbiological indicators and heavy metals. This study demonstrates the feasibility of utilizing G. sulphuraria as an efficient cell factory for NH₄⁺-N removal from wastewater via mixotrophic cultivation, underscoring the potential of pilot-scale, non-sterile, high-protein biomass production to advance microalgae-based “waste-to-treasure” bioconversion and enable cost-effective wastewater treatment.