In-situ algal control by two-stage nanobubble technology in Taihu Lake: Efficacy and ecological impact.

Hydrodynamic cavitation and ozone nanobubble-coupled hydrodynamic cavitation have demonstrated effective algae control in laboratories, but their in-situ potential, especially impact on nutrient salt degradation and microbial communities remain unclear. This study applied two-stage nanobubble technology, combining hydrodynamic cavitation and ozone nanobubbles, in a 3300 m2 semi-enclosed area of Taihu Lake to address these gaps. Results show that the technology efficiently controls algae, reduces odors, improves anaerobic conditions, and lowers ammonia nitrogen. Over 20 days, chlorophyll-a concentration reduced by 77.46% and cyanobacterial phycocyanin by 89.47%. Additionally, the concentrations of 2-MIB, GSM, and DMTS fell below threshold values. Notably, the relative abundance of Cyanobacteria in sediment dropped from 8.53% in the control area to only 1.59%-3.65% in the experimental area. The technology also achieved a significant reduction in ammonia nitrogen, with removal efficiencies of 78.53% in the water column and 39.17% in sediments, though the removal of total phosphorus was limited. Furthermore, the two-stage nanobubble system enhanced the abundance of nitrogen-cycling microorganisms and genes in the water, while promoting nitrogen- and phosphorus-related microbial communities in sediments and inhibiting the cyanobacteria-associated genus Cyanobium PCC-6307. Thus, Two-stage nanobubble technology can be employed for in-situ algal control in aquatic ecosystems.