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The Role of Microorganisms in wastewater treatment

There are two types of microorganisms at work in an activated sludge sewage treatment plant. The first type work to clean the water, while the second type stabilize the heavier materials in the sewage and produce energy.

The Aerobes:

Aerobic bacteria work on the raw sewage in the presence of oxygen to produce carbon dioxide and more bacteria. Sewage contains fecal matter and organics such as food waste, ammonia, soaps, oils, paper, carbohydrates and proteins. To humans this is waste. To aerobic bacteria it is food. Essentially they eat and “burn up” the sewage with their metabolic processes. Before entering our four aeration basins the incoming raw sewage is mixed with established aerobic bacteria. They are recirculated in the aeration basins for about 2-3 hours while bubbling huge amounts of air through the mixtures, The bacteria eat the nutrients in the sewage and turn it into the cells of trillions more bacteria and treated water. Next the flows go to large clarifier tanks where gravity slowly settles the heavier microbes to the bottom and the treated clean water flows out over the top of hundreds of small wiers.

In summary, we provide food and oxygen for the helpful bacteria and they do the work for us!

aeration basin with bubbles rising to surface
One of our four aeration basins where oxygen, sewage and helpful bacteria meet

The Anaerobes:

The collected aerobic bacteria and heavier solids in the sewage are directed into anaerobic (no air) digestors where trillions of anaerobic bacteria live, The anaerobes eat the aerobic bacteria and the heavier solids in the mixture and produce methane as a by-product. The methane is then burned to produce electricity. The mixture is dewatered to create an inert organic mass called biosolids, which is then trucked offsite and is used to enhance compost mixtures for ag crops in the Central Valley.

new anaerobic digester at plant
Our newest anaerobic digester where bacteria turn sludge solids into methane

Learn more about water treatment processes: to read more on these processes.

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