Improving the efficiency of wastewater treatment and microalgae production for biofuels

Microalgae-based wastewater treatment systems are one of the most promising processes to address critical challenges in both climate change and wastewater treatment. The growth of microalgae in wastewater creates feedstock for renewable energy. The wastewater medium provides the essential nutrients for the growth of microalgae, while the treated water can be recycled to reduce the cost of microalgae cultivation. It is therefore worth investigating the factors and optimal conditions of microalgal growth in wastewater systems. Using Scenedesmus quadricauda as the algal species and considering that microalgae are mostly exposed to turbulence, a self-designed oscillating grid device was used to investigate the separate effect of turbulent pulsation. Four hydraulic conditions with different turbulent intensities (turbulent dissipation rates of 0, 1.69 × 10−3, 1.40 × 10−2, 8.32 × 10−2 m2s−3) were combined with agricultural phytohormones (a mixture of gibberellin acid, indole-3-acetic acid and brassinolide) to investigate the effects on biomass accumulation, photosynthetic properties, nutrient removal efficiency, and recycling characteristics from S. quadricauda. Results showed that moderate turbulent intensities and mixed phytohormones provided optimal operating conditions to meet nutrient removal and recycling performance. Biomass concentration and lipid yield increased by 24.78% and 70.00% respectively compared to the stationary group. The highest removal rates of 77.49% and 65.17% were achieved for ammonia nitrogen and phosphate treatments, respectively. Further, the optimum microalgal species, the appropriate nutrient profiles of wastewater and the economic value of microalgae were discussed.