Clean Water Superstar #3: Aerobic wastewater bacteria

Every month, the Clean Water Initiative Program will be highlighting a Clean Water Superstar. These are species that help keep our state’s water resources swimmable, drinkable, and fishable. February’s Clean Water Superstars are aerobic wastewater bacteria! Throughout the month, there will be information, resources, pictures, and videos about these superstar organisms posted on the Clean Water Vermont Facebook page.

If you live in a city or village, whenever you turn on the sink or flush a toilet, the water travels to a wastewater treatment facility. After being screen to remove trash and large material, the wastewater flows through settling tanks where most of the sludge and large particles fall to the bottom. Next, the wastewater is transported to the aeration tanks where February’s Clean Water Superstars live. These organisms are far too small to see with the naked eye, ranging in size from half a millionth of a meter to two millionths of a meter, but they have a big impact on water quality. There can be as many as 300 different species in a single aeration tank. They are aerobic bacteria!


The aeration tank at the wastewater facility in Hartford. Photo credit: Amy Polaczyk, VT Department of Environmental Conservation

Aerobic bacteria need oxygen, making them different than other kinds of bacteria. Oxygen is continually pumped into the aeration tank at the wastewater treatment facility, providing the perfect habitat for the bacteria to do what they do best – grow, reproduce, and ingest wastewater particles. The aerobic bacteria consume organic material, anything that was once alive, thereby removing nutrients and contaminants from the water. If this excess organic material was released into a river or other waterbody instead of being treated at the wastewater facility, the naturally occurring bacteria and decomposers would consume it, using up all of the available oxygen that invertebrates, fish, and most other organisms rely on, creating dead zones. In the aeration tank, however, the bacteria can use as much oxygen as they need while ingesting the organic matter, so when the water is released to the river, there is very little for bacteria to consume, keeping lake or river oxygen levels intact.


The dark brown clumps are floc, which contain bacteria, protozoans, algae, and particles from the wastewater. A type of protozoan called stalked ciliates are shown here. Photo credit: Paul Olander, VT Department of Environmental Conservation

Larger organisms – protozoans – such as ciliates, flagellates, and rotifers also live in the aeration tanks and feed on bacteria and particulates in the wastewater. Aside from the quantity and contents of the wastewater, other factors influence these organisms and the aerobic bacteria in their aeration tank ecosystem. These include temperature, pH, alkalinity, and dissolved oxygen. Operators of the wastewater treatment facility must continually monitor and occasionally adjust these factors to keep the ecosystem thriving. Operators also monitor the aeration tanks by looking at wastewater samples under a microscope to view the protozoan community. The bacteria themselves are too small to be seen without specialized equipment, so the quantity and diversity of protozoans indicate if the ecosystem can support a healthy population of bacteria as well. The goal of facility operators is to cultivate the appropriate amount and diversity of bacteria and protozoans for the most efficient and thorough cleaning of the water. So remember, any time organic material goes down the drain at your home or office, February’s Clean Water Superstars are at the other end of the pipe helping clean and protect our waters.

For more information, visit the Clean Water Vermont Facebook page, and stay tuned for the next blog post about species used in green stormwater infrastructure.

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