Modern waste water treatment is a very complicated and long and involved process. There are many themes involved and many processes that can be used to achieve different outcomes for the water. The exact process that will be used for a specific water treatment plan will depend on the desired outcome for the water, which is based on what the water will be used for in the end. When the overall process has to be varied, the steps that are involved in the process will have to vary as well. There are many different steps that can be used in a water purification process depending on the desired outcomes, but the general categories of the steps and processes used will stay the same.
The first step in any water purification process, regardless of scale, is generally passing the water through a coarse filter to remove large debris, such as plant matter, plastic and metallic trash, and stones and sand that may be present in the water. It is highly important to filter these components out before they reach the later steps of the water purification process because they can lead to the clogging of pipes and filters, and it is generally very difficult to remove debris from other water purification process components.
Once large debris is removed, then the more varied steps of the water treatment process can begin. Generally, one of the first steps involves neutralizing any bacteria, fungi, algae, or any other biological contaminants that may be present in the water. This can be done by several methods, which include chlorination, chloramination, or UV irradiation. UV treatment is mostly suitable for smaller scale water treatment processes, while chlorination is used in larger scale processes. This step of the process is highly important, as biological contaminants can be health hazards if the water is for human consumption as well as causing biofouling and bioslime buildup in other industrial uses.
After biological contaminants are removed, water is usually treated with an activated sludge process. The purpose of this treatment is to degrade common contaminants of water including waste compounds as well as pharmaceutical contaminants. Additionally, many contaminants that are not degraded by the activated sludge get adsorbed to the surface of the sludge bulk and are removed from the water that way. This treatment can be followed with further purification depending on the end goals of the process.