What Are The 8 Steps Of Sewage Treatment?

by Anna

Sewage treatment plays a crucial role in maintaining environmental health by purifying wastewater before it is released back into natural water bodies. The process involves a series of meticulous steps to remove contaminants and ensure the safety of our ecosystems. In this article, we will delve into the eight essential steps of sewage treatment and explore the significance of each in safeguarding the environment.



The initial step in sewage treatment is screening, where large objects like sticks, leaves, and plastic are removed from the wastewater. This is achieved through the use of bar screens or gratings that allow water to pass through while capturing larger debris. By eliminating these coarse materials, the subsequent treatment processes become more effective, preventing damage to downstream equipment.


Primary Treatment:

Following screening, the sewage undergoes primary treatment, a process that focuses on the removal of suspended and settleable solids. The wastewater is directed to sedimentation tanks, allowing the heavier particles to settle at the bottom as sludge, while the lighter materials float to the surface as scum. The clarified water, now with reduced solids, is then transferred for further treatment. The sludge generated in this step is often subjected to additional treatment for safe disposal or beneficial reuse.

Secondary Treatment:

Secondary treatment is a biological process designed to remove dissolved and suspended organic matter that escapes primary treatment. Microorganisms, including bacteria and other microbes, are employed to break down the remaining organic substances in the water. Common methods for secondary treatment include activated sludge processes, trickling filters, and oxidation ponds. These processes enhance the water quality by significantly reducing the biochemical oxygen demand (BOD) and ammonia levels.

Tertiary Treatment:

To achieve a higher level of purity, some sewage treatment plants incorporate a tertiary treatment stage. This step involves additional processes to further refine the water quality. Common tertiary treatment methods include filtration, chemical precipitation, and advanced oxidation. Filtration helps remove remaining fine particles, while chemical precipitation involves the addition of chemicals to facilitate the settling of impurities. Advanced oxidation employs processes like ultraviolet (UV) irradiation to eliminate persistent contaminants, ensuring that the treated water meets stringent quality standards.


Disinfection is a critical step to eliminate harmful pathogens, such as bacteria, viruses, and parasites, from the treated wastewater. Chlorination, ultraviolet (UV) irradiation, and ozonation are common disinfection methods. Chlorination involves the addition of chlorine to the water, effectively killing bacteria and other microorganisms. UV irradiation exposes the water to ultraviolet light, disrupting the DNA of pathogens and rendering them inactive. Ozonation employs ozone gas to oxidize and destroy contaminants. Proper disinfection ensures that the treated water is safe for release into the environment or for reuse.

Sludge Treatment:

The sludge produced during primary and secondary treatment contains a mixture of organic and inorganic materials. Proper sludge treatment is essential to minimize environmental impact and ensure safe disposal. Various methods, including anaerobic digestion, aerobic digestion, and dewatering, are employed to reduce the volume of sludge, stabilize its organic content, and facilitate proper disposal or beneficial reuse. Some treated sludge may be converted into biosolids, which can be used as fertilizers or soil conditioners.

Nutrient Removal:

Excessive levels of nutrients, such as nitrogen and phosphorus, in treated wastewater can lead to environmental issues like eutrophication in receiving water bodies. Therefore, some sewage treatment plants incorporate nutrient removal processes. Biological nutrient removal (BNR) utilizes specific microorganisms to convert nitrogen and phosphorus into gaseous forms that can be released harmlessly into the atmosphere. Alternatively, chemical methods may be employed to precipitate and remove these nutrients from the water.

Effluent Disposal or Reuse:

The final step in sewage treatment involves the responsible disposal or beneficial reuse of the treated effluent. Depending on local regulations and environmental considerations, the treated water can be released into rivers, lakes, or oceans. Alternatively, it can be used for non-potable purposes such as irrigation, industrial processes, or groundwater recharge. Responsible effluent management is crucial to prevent adverse impacts on aquatic ecosystems and to support sustainable water resource management.

See Also: What Are The 3 Types Of Sewage Treatment?A Complete Overview


The eight steps of sewage treatment collectively form a comprehensive process aimed at purifying wastewater and safeguarding the environment. Each stage plays a vital role in removing impurities, contaminants, and pathogens to ensure that treated water meets stringent quality standards. By understanding and implementing these steps effectively, sewage treatment facilities contribute significantly to environmental conservation and the sustainable use of water resources. As populations grow and urbanization continues, the importance of proper sewage treatment becomes even more pronounced, emphasizing the need for continued innovation and investment in wastewater management practices.


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