Nutrient, CO_2, and H₂S were efficiently removed in algal-bacterial processes.

The mixed culture containing Scenedesmus obliquus achieved the best combined effects.

Activated sludge supported a superior biogas slurry treatment performance.

The peak carbohydrate content of containing S. obliquus was 75.24% under 55% CO₂.

Maximum biomass productivity of 0.177 gL⁻¹ d⁻¹ was recorded under 45% CO₂.