Now that we understand the physiologies of microbes and their roles in the carbon and N cycles we can apply that knowledge to environmental problems. Waterborne pathogens 2. Because of the public health and environmental problems associated with sewage, municipalities in the U.S. are now required to treat waste water using at least a secondary wastewater treatment system. Figure 41.17 shows a typical secondary wastewater treatment plant. Note the difference between primary and secondary treatment.
Primary treatment is just a means to separate the solid from the liquid waste.
Most of the microbiological action takes place in the secondary stages of treatment. Analogous to a continuous flow process. More of a batch process in which air is bubbled through the activated sludge unit and the microbes grow as flocs. After the secondary clarifier the fluid is usually chlorinated and discharged into a body of water. Note that most of the sludge from the first and last steps ends up in the anaerobic sludge digestor .