Biogranulation process facilitates cost-efficient resources recovery from microalgae-based wastewater treatment systems and the creation of a circular bioeconomy

Energy self-sufficient wastewater treatment designs can reduce net energy consumption and achieve resources recovery. Microalgae are regarded as a promising candidate for developing a circular bioeconomy in wastewater treatment plants (WWTPs) due to its potential for simultaneous wastewater remediation and high value-added materials production. Much effort has been made to overcome the high production costs for microalgae; however, biomass harvesting still remains as the bottleneck for its large-scale application. In this study, the novel biogranulation system facilitating easier and faster microalgae harvesting was firstly compared with the conventional suspended culture for energy-efficiency and sustainability assessment on microalgae (Ankistrodesmus falcatus var. acicularis) cultivation using the synthetic anaerobic digestion liquor. Results demonstrated that the biogranulation system enhanced volumetric bio-mass productivity (223.17 +/- 11.82 g/m(3)/day) by about 4.4 times compared to that from the suspended system (41.57 +/- 2.08 g/m(3)/day) under the same environmental conditions. It was noticed that lipids, carbohydrates and pro-teins were accumulated in microalgae cells along with nutrients remediation, and the microalgae granules with much higher proteins content (313.28 +/- 26.67 mg/g-VSS) could be easily harvested through 2 min gravity sedimentation with little impact on the contents of carbohydrates and lipids. In the whole cultivation and harvesting process, the bio-mass mass-based electricity consumption and footprint demand by the biogranulation system were reduced by 58% and 76%, respectively. Results from this study provide a cost-effective and sustainable approach for microalgae in the treatment of nutrients rich digestion liquor with simultaneous production of valuable biomaterials.

Automated summary

This study compared a novel biogranulation system with a traditional suspended culture system for microalgae cultivation, and found that the biogranulation system significantly improved biomass productivity and facilitated easier harvesting of microalgae.