We are testing the use of local, natural bacteria to destroy cyanotoxins. These toxins are produced by freshwater cyanobacteria, also known as blue-green algae, and they contaminate municipal water supplies. First we will determine which natural bacteria work best and then we will develop a new, commercial-size biological filter for cyanotoxins. This filter will be used by water treatment facilities to remove cyanotoxins from drinking water.
Why We Care
Cyanotoxins are some of the most potent natural toxins known. They can cause rapid death by respiratory failure. Human consumption of contaminated drinking water can lead to liver damage and lasting harmful effects on the immune system down to the cellular level. Recreational exposure, such as swimming, can result in stomach, intestinal, and respiratory problems and skin rashes. There are several cyanobacteria species that produce “cyanotoxins.” Blooms of cyanobacteria Microcystis can produce high concentrations of a cyanotoxin called microcystin that can poison and even kill animals and humans. Cyanotoxins can also accumulate in other animals, including fish and shellfish, and poison animals that eat them. Cyanotoxin contamination of farm and ranch ponds is well known to kill livestock and dogs. Most recently, cyanotoxins have been implicated in causing or enhancing neurological diseases such as Alzheimer’s, Parkinson’s, and amyotrophic lateral sclerosis.
There is tremendous worldwide demand for safe, reliable, and affordable systems to clarify water. Chlorination works well to remove microcystins in laboratory experiments but often fails under real-world situations of high dissolved organic carbon, such as the conditions found during a toxic cyanobacterial bloom. Many water supply providers are increasingly replacing chlorination with chloroamine or chlorine dioxide to decrease the formation of toxic chlorinated byproducts. These chemicals have an even lower efficiency for removal of microcystin toxins. Ultraviolet treatment by itself is also ineffective for removing microcystins and, while addition of the photocatalyst titanium dioxide greatly improves the process, it is not cost effective. Bank filtration and biological active slow filtration through sand offer cost-effective mechanisms to remove microcystins from the water column, but they can take weeks to months to be effective.
What We Are Doing
We are focusing on microcystins and looking at the materials, facilities, and costs to create a commercial-size microcystin biofilter or reactor. Research during the past 10 years has demonstrated bacteria that co-occur in the environment with toxic cyanobacteria blooms have the ability to break down cyanobacteria toxins, such as microcystin, and use them as an energy source. The University of Tennessee has isolated these types of organisms from Lake Erie, and has acquired the bacteria from Australia originally found to degrade microcystins. We will identify new microcystin-degrading bacterial species and study how well they destroy microcystins found in the Great Lakes. Field samples are being collected from western Lake Erie, Lake Ontario, and international locations such as Lake Tai (Taihu) in eastern China. We will determine the rates of biological microcystin decomposition and identify chemical end products and environmental factors that influence temperature and nutrient availability. We will identify any National Environmental Policy Act (NEPA) requirements for using the biofilter to degrade microcystins from natural water bodies. The goal of this phase of the study is to develop and operate a biological “digester” or biofilter under “pilot plant” conditions, similar to those currently used for the removal of persistent organic chemicals.
This work is part of the Prevention, Control, and Mitigation of Harmful Algal Blooms (PCMHAB) program. The project team includes partners from the University of Tennessee, Knoxville and the State University of New York College of Environmental Science and Forestry, Syracuse.
Benefits of Our Work
This project is an essential first step for preparation of a large-scale biological filtration system to mitigate and prevent microcystins from getting into water distribution systems. Potential customers include resource managers and public and private potable water providers, and may include hospital, aquaculture, agriculture, and recreational waterbody managers. We have established an advisory team to address engineering and regulatory challenges for use of this technology in existing water facilities. This team includes a representative from a large water engineering firm and NEPA experts to help guide the early development of the technology.
What We Found This project, "Developing Practical and Affordable Water Filtration Systems to Remove Cyanotoxins," did not achieve one of its original goals: testing a microcystin biofilter/reactor using microcystin-degrading bacteria. However, a number of potential natural occurring microcystin-degrading bacterial were isolated and new information was learned about the microcystin degradation pathway. This line of research (i.e., using bacteria to degrade microcystins in a portable filtration system) appears to be more complicated to undertake than originally thought.
A peer-reviewed research paper was published by the project investigators in late 2019 describing project findings concerning the traditionally understood microcystin degradation pathway, the mlr gene “cassette.” Collectively, the observations in the study raise interesting questions about the specificity, diversity and ubiquity of microcystin biodegradation pathways in the environment.