Field-scale evaluation of nanobubble ozone technology for cyanobacterial harmful algal bloom control

Effective Cyanobacterial Harmful Algal Bloom (CHAB) control strategies are needed to address recreational and drinking water impacts. Nanobubble ozone technology (NBOT) is an emerging treatment, but field-scale studies are limited. An 18-week NBOT treatment trial was conducted on a 42-acre CHAB impacted Ohio recreational lake in 2021. The trial was split into low ozone dose (60 g/h), higher dose (180 g/h), and pre- and post-treatment periods. Two multi-parameter sondes recorded continuous data and water samples and profiles were collected weekly at six sites and analyzed for nutrients, cyanotoxins, phytoplankton diversity and abundance, and additional parameters. Multi-spectral imagery was captured on seven drone flights and sediment cores were collected. Cyanobacteria chlorophyll concentrations sharply declined and remained low for four weeks after the ozone dose was increased, but concentrations increased in response to a 4.5” rain event. Microcystins and saxitoxins peaked at 2.5 and 4.0 µg/L during the low dose treatment period, then declined after increased ozone dose. Recreational CHAB advisories were not posted, in contrast to past summers. Residual ozone was only detected at NBOT unit locations, but ozone concentrations increased in held samples demonstrating potential for nanobubbles to release ozone over time. Additional NBOT trials are planned for 2022.