Different Kinds of Wastewater Treatment Plants

sewage treatment process

Before getting into sewage treatment, let us first look at what sewage treatment chemicals are and how they work. Sewage consists of both human waste and animal waste. Usually, sewage treatment involves the separation of the harmful and helpful components in the waste. Then these components are injected or sprayed into underground aquifers to separate the bad from the good.


Sewage treatment plants generally use three main processes for the separation of the two categories of waste. The first is known as coagulation. Coagulation involves the pressing of hard materials against solid surfaces in a non-cohesive solution. This is followed by the precipitation of the material with a slurry composed of lighter and coagulating material. The final step is the concentration and elimination of the heavier liquid or sludge with the aid of aqueous solutions, steam or water.

Phases of Coagulation

Among all the different phases of coagulation, the most critical and important stage is the removal of excess sludgy deposits. Also, it is one stage that is particularly important for sustaining water quality. There are several ways of removing excess sludgy deposits such as surface water dosing, coal bed coagulation, and wet dosing. It is very important to select the right method depending on the type of sludgy deposits. Surface dosing is used when there are no restrictions on the discharge of untreated sewage.

Coal bed coagulation uses high-temperature heat and the application of coagulated minerals with a crushed stone or steel wire. The sludgy deposits are first heated and then the heated coagulated deposits are placed over the sewage treatment sludge to precipitate it. The sludgy deposits are generally deposited by high pressure. The process is similar to the hydrocarbon limestone sludge deposit in that it can take years for it to be developed. Coal bed sludgy deposits are also very common in the northern parts of the United States and are capable of taking hundreds of years before they are developed enough to produce a noticeable difference in the sedimentation rate.

sewage treatment process

Approaches to the Process

When dealing with sewage treatment in a municipal setting, there are several approaches to this process including activated carbon and coagulation. Activated carbon is a process where light is used to attach pollutants such as pesticides to the metal electrodes in sewage so that they can be removed from the water during treatment. Coagulation, on the other hand, involves the use of pressurized hot water to coagulate the sediments in wastewater before they can break down into microscopic granular materials that can then be removed from the water using a filtration system.

Another term that you might come across while researching sewage treatment chemicals is biocide or superphosphate. This is a highly concentrated form of the chemical that is often added as a last resort to kill bacteria during sewage treatment. The bacteria would die if not for the biocide, and it also kills harmful and beneficial microorganisms in the water that can cause water pollution. It is usually added at the end of the sewage treatment plant’s life cycle because it does not dissolve easily, and it can be removed through normal sewage treatment processes.


Disinfectants are added in wastewater treatment plants to prevent the introduction of disease-causing cysts in water. These disinfectants usually come as granular carbon, chlorine, bromine, chlorination (via a combined process of chlorination and disinfection), or a combination of disinfectants. These chemicals are usually used in conjunction with secondary treatment in the form of algaecide and other water treatment products. Wastewater treatment plants are responsible for removing most of the cysts present in sewage.