A wastewater treatment facility is one that takes water from sanitary and possibly storm sewers and sends it through a process of purification to remove harmful contaminants. The water may then be released into the environment or used for other purposes. Most treatment facilities are owned by local governments, though some are also owned by regional, state, or even federal governments. In order to clean the water, the wastewater treatment facility usually runs the water through at least three steps: preliminary treatment, primary treatment, and secondary treatment.
The entire wastewater treatment system is housed in the wastewater treatment facility, except for the sewer lines that bring the water to the plant. Once there, the water will go through the series of steps using specialized equipment and organic compounds. This process not only involves using mechanical and biological processes, but also giving the water time to sit so that contaminants settle. In addition to the three basic steps, the wastewater treatment facility may add extra steps, depending the water's intended use.
The preliminary treatment step does not do much other than take out the larger solids that come through the sewer line with the water. These are strained out using metal bars spaced close together to catch the larger pieces of material. Most of the solids at this level will likely be taken to a local landfill, unless there is some sort of biological concern. Some sorting may also be required. It is also during this stage, after the initial screening, that the water will be allowed to sit so that solids not caught in the filter can settle.
Primary treatment is the next step in the process. This step removes another round of solids by allowing further settling to occur. As solids settle to the bottom, oils and other contaminants may also come to the top, both of which are removed. After this separation occurs, the water is moved on to the next step in the process. It is important to remember the water can still hold many harmful materials even after this stage.
The secondary treatment step is where many of the biological dangers are removed. In this step, aeration and micro-organisms work to take care of the other dangerous organisms left in the water, which is then allowed to settle again. Water that is going to be used for drinking or released into a natural environment may be disinfected, usually with chlorine or ultraviolet disinfection, before being released. The chlorine will also need to be removed. Not all water effluent coming from a wastewater treatment facility will require chlorination.