Wastewater is the water supply of a community after it has been soiled by use. It may contain human and household wastes, industrial wastes as well as groundwater and, in many cases, stormwater runoff. Before it can be safely returned to the environment, the wastewater must be treated. The treatment process can range from relatively simple to very complex. The specific process used for treatment will vary with the source and volume of wastewater to be treated. For most communities, a system similar to the diagram below provides treatment to remove solids, materials that will consume oxygen and organisms that could potentially cause disease if released to the environment.
- Preliminary Treatment — Removes debris which could damage plant equipment
- Primary Treatment — Removes 90 - 95% of the settleable solids.
- Secondary Treatment — Removes organic matter through biological oxidation and settling.
- Advanced Treatment — Removes solids, nitrogen, phosphorus, and other pollutants such as color and metals.
- Disinfection — Removes organisms which might cause disease.
- Solids Handling — Treats the solids removed from the wastewater to allow safe and economical disposal.