Microalgal wastewater recycling: Suitability of harvesting methods and influence on growth mechanisms

Wastewater recycling helps address the challenge of microalgae biomass commercialization by allowing for efficient resource recovery. In this study, three conventional harvesting methods, including centrifugation, microfiltration, and flocculation sedimentation, were investigated to explore the effects of harvesting methods on the characteristics of recycled wastewater and the growth of microalgae to select a suitable harvesting method for the microalgal waste-water recycling system. During the wastewater recycling process, the least amount of accumulated substances was ex-hibited in the wastewater recycled by microfiltration, followed by centrifugation, and the most by flocculation sedimentation. After 4 batches of cultivation, microalgal biomass harvested from centrifugation wastewater and microfiltration wastewater was 21.26 % and 13.54 % higher than that from flocculation wastewater, respectively. Lipids, carbohydrates and pigments were all increased by varying degrees. Additionally, flocculation sedimentation was not suitable for the microalgal wastewater recycling process since the low residual nutrients, high salinity, and ex-cessive algal organic matter severely inhibited the growth of microalgae. Under the regulation of phytohormones, microalgae increased their energy reserves, enhanced photosynthesis, and improved their defense capability to resist the increasing abiotic stress. This study provides scientific support for the selection of suitable harvesting technology during the microalgal wastewater recycling process.

Automated summary

Wastewater recycling addresses microalgae biomass commercialization challenge by allowing efficient resource recovery. This study compared three conventional harvesting methods – centrifugation, microfiltration, and flocculation sedimentation – to select a suitable method for microalgal wastewater recycling. Microfiltration resulted in the least accumulated substances in recycled wastewater, followed by centrifugation and flocculation sedimentation. After four cultivation batches, microalgal biomass harvested from centrifugation and microfiltration wastewater was 21.26% and 13.54% higher than that from flocculation wastewater, respectively. Lipids, carbohydrates, and pigments all increased to varying degrees. Flocculation sedimentation was not suitable due to low residual nutrients, high salinity, and excessive algal organic matter inhibiting microalgae growth. Under phytohormone regulation, microalgae increased energy reserves, enhanced photosynthesis, and improved defense against abiotic stress. This study provides scientific support for selecting suitable harvesting technology for microalgal wastewater recycling.