Hybrid microalgae-activated sludge system for carbon-efficient wastewater treatment

Engineered microalgae-bacteria systems can play a key role in the realisation of energy-efficient carbon-neutral wastewater treatment technologies. An attempt was made to develop a hybrid microalgae-activated sludge (HMAS) system coupling carbon capture with domestic wastewater treatment. Photobioreactors internally illuminated with red light-emitting diodes (LEDs), and inoculated with mixed microbial culture, resulted in substantial savings in operational cost. System performance was evaluated at about 600 μmol/m² s LED irradiance while treating synthetic municipal wastewater in a chemostat for about 2 months, containing about 250 mg/L soluble chemical oxygen demand (SCOD), 90 mg/L NH₃-N and 10 mg/L orthophosphate. Carbon dioxide was supplied into the HMAS at 25 mL/min, 25% v/v. SCOD was efficiently removed from the wastewater (up to 70%) and bacterial oxygen requirement of >2 mg/L was met through microalgal photosynthesis. The system demonstrated its potential in achieving carbon-efficient wastewater treatment.