Synergistic pollutant removal and high-value biomass production via Galdieria sulphuraria-based starch wastewater treatment

This study presents a biological treatment system using the extremely acidophilic microalga Galdieria sulphuraria to treat highly acidic and organic-rich starch wastewater. G. sulphuraria thrives in acidic (pH 3.5-4.0) and thermophilic (35-45 °C) conditions, effectively treating starch wastewater without the need for pH adjustment. After acclimation, G. sulphuraria achieved removal efficiencies of 77.9 % for chemical oxygen demand, 82.8 % for total nitrogen, and 70.7 % for total phosphorus within 12 days, while yielding 4.48 g/L of biomass. In addition, the proposed system exhibited high stability and resistance to contamination, with G. sulphuraria maintaining a relative abundance greater than 96.0 % throughout the treatment period. This ensures the feasibility and ease of maintenance of the treatment process in practical applications. Compared to conventional anaerobic-aerobic processes, the proposed system produced a higher carbon conversion ratio (59.4 %) and overall carbon conversion ratio (46.2 %) while using wastewater as a free nutrient source to produce high-value products. The harvested G. sulphuraria biomass contained 45.0 % protein (41.9 % essential amino acids) and 16.4 % lipids; essential fatty acids comprised over 55 % of the total fatty acid content. These characteristics make G. sulphuraria suitable for use as animal feed or food additives, as well as for biodiesel production. Thus, G. sulphuraria offers a potentially low-carbon, environmentally friendly approach for the resource-oriented treatment of starch wastewater.