Despite significant efforts to improve water treatment processes to address harmful algal blooms, some drinking water treatment plants in Ohio struggle to effectively remove cells of cyanobacteria and their associated algal organic matter.
This is largely due to a step in the treatment process called sedimentation, in which particles with a higher density than water are separated out using gravity. Cyanobacterial cells, which naturally float on water due to their low density, aren’t effectively removed through this process. This step also requires high doses of chemicals for cyanobacteria removal, generating large amounts of leftover chemical waste.
“Many small drinking water treatment plants face significant challenges in managing high levels of algae and elevated algal organic matter while ensuring safe drinking water production,” said Dr. Youngwoo (Young) Seo of The University of Toledo. “Although managers and operators work diligently to provide safe water, there is a critical need to optimize treatment processes using scientific data.”
Researchers conducted full-scale tests of dissolved air filtration at the Celina drinking treatment water plant. The plant takes its source water from Grand Lake St. Marys, which experiences chronic and severe harmful algal blooms with a very high level of toxins throughout the year.
Recently, a team of researchers led by Seo have optimized the chemical treatment for dissolved air flotation (DAF) as a cost-effective alternative for treating water impacted by harmful algal blooms (HABs). Within this system, billions of microscopic air bubbles attach to contaminants and float them up to the water surface, where they can be skimmed off and separated. The research was funded through the Ohio Department of Higher Education’s Harmful Algal Bloom Research Initiative (ODHE HABRI).
Previous studies showed that DAF can effectively remove cyanobacteria from water while using fewer chemicals, yet scientists were unsure how to optimize the process based on the composition of organic matter in the water.
Through the project, Seo’s team tested the performance of DAF using laboratory experiments and a full-scale study at a drinking water treatment plant in Celina, OH. The plant sources its water from Grand Lake St. Marys, which experiences chronic, severe HABs with high levels of toxins throughout the year.
In the lab, researchers worked to optimize chemical treatment for the system, considering the impacts of organic matter during HAB events. Then, at the plant, the team monitored the long-term performance of a DAF system by tracing the fate of cyanobacteria and toxins. Finally, researchers used their findings to develop guidelines for DAF operation and management, offering practical advice for water treatment plant operators.
In addition to water treatment plant tests, pictured above, the team conducted laboratory experiments at The University of Toledo, working to optimize chemical treatment for the system, considering the impacts of organic matter during HAB events.
The study yielded significant outcomes. From the lab tests, the team identified the best chemical types and doses to use in DAF systems. Meanwhile, the full-scale system installed at the Celina plant is the first of its kind in Ohio to treat water impacted by HABs. Researchers made recommendations to the plant and are monitoring its impacts, collecting and analyzing samples biweekly.
“By applying these optimized chemicals and doses, the Celina DAF system produced much clearer water, significantly improving the performance of downstream treatment processes,” Seo said.
The team compared drinking water treatment residuals from the Celina water plant with other plants in Ohio that employ conventional processes to treat raw water from Lake Erie. This comparison will soon help support sustainable waste management practices, such as applying residuals (byproducts and waste from water treatment) to farm soils. Researchers also examined how effectively different treatment methods can “deactivate” harmful algal toxins in waste streams.
On a broader scale, the project will directly impact over 10,000 residents in Mercer County, OH, by providing safe potable water at the Celina treatment plant. The methods developed by Seo’s team will help remove algal toxins from water with lower energy and fewer chemicals, making water treatment more efficient and cost-effective.
“Over 2.5 years of collaboration, we gained valuable insights into the treatment process and addressed many scientific questions,” Seo said. “This project exemplifies mutual support and collaboration to better serve our communities. Additionally, undergraduate and graduate students involved in the project benefited from service-based learning and educational experiences, witnessing firsthand the impact of community-serving research.”
Ohio Sea Grant is supported by The Ohio State University College of Food, Agricultural, and Environmental Sciences (CFAES) School of Environment and Natural Resources, Ohio State University Extension, and NOAA Sea Grant, a network of 34 Sea Grant programs nation-wide dedicated to the protection and sustainable use of marine and Great Lakes resources. Stone Laboratory is Ohio State’s island campus on Lake Erie and is the research, education, and outreach facility of Ohio Sea Grant and part of CFAES School of Environment and Natural Resources.