Microbes that Clean Sewage

Microbes are very small creatures, so small that they can only be seen with a microscope. They live in sewage and are very useful to us because they clean sewage water and make it possible for us to use the water again. They are so small that until the early part of the twenieth cenury people did not know of their existence or the good they were doing cleaning up sewage.
     

Now that people know about microbes and how they live, they encourage them in their work of cleaning sewage. Microbes need oxygen and as long as they are provided with air they multiply and work very rapidly. Sewage treatment works use different methods of supplying air to microbes. At the sewage works on the River Lea compressed air is forced through sewage water.

Here is a picture of aeration tanks at Deephams Sewage Works.

There are many different kinds of microbes working in sewage, the most common belong to one of two groups: bacteria and protozoa.

Bacteria are much smaller than protozoa and look like dots or rods, but protozoa come in many interesting shapes. Here are some protozoa.

What the bacteria do is eat the sewage. As it passes through their bodies it changes into carbon dioxide, water and other harmless substances. However, if left to the bacteria alone, there would be so many of them that the treated sewage would end up cloudy. That's where the protozoa come in. They eat some of the bacteria. Sewage treatment works have to be carefully operated to keep the right balance between bacteria and protozoa. The treated sewage still needs further treatment for us to drink it, but it is clean enough to go into the river without harming the river life too much.

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