Types of Bacteria in Sewage Plants

Sewage plants must treat wastewater to make it possible to return it to the environment without causing pollution or spreading disease. At different stages of the treatment process, you may find several types of bacteria in the water. While some bacteria are harmful and are removed from the raw sewage, other bacteria may be helpful.

Coliform bacteria include fecal coliform, such as the E. coli bacteria. Typically, these coliform bacteria exist in water where human or animal fecal matter is present. As such, they can be helpful to the sewage treatment process, indicating the level of fecal contamination and the presence of other bacteria. The coliform bacteria, themselves, can be harmful in certain quantities, causing diarrhea, cramps, nausea or headaches if ingested, more so for young children, the elderly or people with weakened immune systems. In addition, coliform bacteria indicate the presence of microbes such as the coliophage virus or enterococci bacteria. These pathogens can also cause short-term health effects similar to the coliform bacteria, including diarrhea and vomiting, if ingested.

Acetinobacter is one of the most common bacteria found in water throughout the sewage treatment process. It can survive in clean soil and rivers as well as on human skin. It is a relatively harmless bacteria and permissible within cleaned water at certain levels. However, when levels of acetinobacter bacteria become excessive, they may cause illness. One strain, Acetinobacter baumannii, is responsible for about 80 percent of all infections. Potential illnesses range from pneumonia to blood diseases. Because of the potential health risks of exposure to the acetinobacter bacteria, it's one of the principal bacteria that sewage treatment plants remove from wastewater. One criticism of sewage treatment is the potential strengthening of the acetinobacter. Researcher Chuanwu Xi of the University of Michigan has found increased resistance to antibiotics among acetinobacter issuing from treatment plants.

Sulfate-reducing bacteria (or SRBs) can serve a helpful role in the sewage treatment process. As their name indicates, sulfate-reducing bacteria help sulfates bind within water. This process can reduce the levels of arsenic, zinc and selenium, an important process in water purification, especially when filtering drinking water. Researcher Matthias Labrenz of the University of Wisconsin-Madison found that desulfobacteriaeceae bacteria served especially well at sulfate-reduction. Unlike other SRBs, desulfobacteriaeceae can survive in oxygen-rich waters, making them more useful to sewage treatment applications. The bacteria work by binding minerals into tiny spheres; Labrenz' trails showed an effect so drastic that the zinc concentration within the bound spheres exceeded the concentration in the water by one billion times.