Optimization of biomass production and nutrients removal by Spirulina platensis from municipal wastewater

- The optimum conditions for microalgal autotrophic cultivation were predicted and validated.
- Mixotrophic cultivation enhanced the microalgal production, and nutrients removal and recovery from wastewater.
- TProper additional dosage of glucose in mixotrophic culture is an effective enhancement of microalgae growth.

Using wastewater as a medium to cultivate microalgae is regarded to have economic and environmental potentials for producing biomass, recovering nutrients and treatment of wastewater. However, low strength of municipal wastewater may influence the optimum conditions for microalgae cultivation while comparing with standard media. In this study, to optimize the microalgal production and nutrients uptake from wastewater, the optimum conditions for microalgal autotrophic cultivation were predicted by using response surface methodology (RSM) and validated through laboratory experiments. The optimum conditions for the cultivation of Spirulina platensis in synthetic municipal wastewater (SWW) were the range of 8.8-8.9 for pH, the light intensity of 3300-3400 lx in the daily illumination time for 12 h when the temperature was set at 25 ± 1 °C with the air-bubbling of 0.5 vvm. Under the optimum conditions, the yield of microalgal biomass and protein content was 262.50 mg/L, 46.02%, respectively. Nitrogen and phosphorus removal efficiencies from SWW were 81.51 and 80.52%, and the nutrients recovery efficiencies in the removed TN and TP were 92.58 and 94.13% in autotrophic culture. The mixotrophic cultivations enhanced the microalgal production, nutrients removal and recovery, and mitigated nutrients limitation. Moreover, the addition of 300 mg/L glucose in mixotrophic cultivation, as a low-cost alternative, was found to be a suitable medium for effective enhancement of microalgae growth, nutrients removal and recovery. These strategies can be a good reference for the enhancement of microalgal production and their application for the large-scale wastewater treatment under a controlled environment.