Sewage treatment is the process of removing contaminants from wastewater, primarily from household sewage. It includes physical, chemical, and biological processes to remove these contaminants and produce environmentally safe treated wastewater (or treated effluent). A by-product of sewage treatment is usually a semi-solid waste or slurry, called sewage sludge, that has to undergo further treatment before being suitable for disposal or land application.
SEWAGE TREATMENT PLANT
Sewage Treatment Plant
Sewage is wastewater generated by households, hotels, and may contain industrial waste water.Sewage typically has a high concentration of organic wastes but may also contain inorganic wastes. Sewage must be treated before it can be discharged into any water body.Sewage, if allowed to enter water sources without treatment, will contaminate them; thus, it is vital to treat sewage adequately before releasing it into rivers or streams.
In a sewage treatment plant, wastewater is treated through primary, secondary, or biological, and tertiary stages in order to enhance its quality for recycling.
What is the working principle of a STP plant?
A Sewage Treatment Plant (STP) operates on the principle of treating wastewater using a variety of physical, biological, and chemical processes to remove pollutants and impurities. The fundamental principle is to imitate and improve natural environmental water purification processes.
This is accomplished by encouraging the growth of helpful bacteria that degrade organic matter, settling solids, and disinfecting the water to ensure that it meets quality standards before being released or reused.
Primary Treatment
In a sewage treatment facility, sewage water initially passes through screens or a grit chamber to remove big solids. This is followed by aeration/mixing in a tank, then primary sedimentation, which settles suspended solids. The primary treatment comprises the addition of a coagulant and seeks to remove grits, coarse solids, oil, and grease, if present. Solids (sludge) settle during preliminary treatment, resulting in the creation of an effluent that floats above the sludge. Effluent from the first treatment contains 45-50% unstable organic materials. The effluent is subsequently subjected to secondary treatment, which involves the separation of fine solids by bacterial activity.
Secondary Treatment
This step uses biological activity to transform organic waste in sewage into stable forms, which leads to secondary sedimentation. Trickling filters and the activated sludge technique are also popular approaches.
A trickling filter is an enclosed tank with a brick bed and a layer of microorganisms. The effluent enters the tank through an inlet and is sprinkled over the bed layer using sprinklers. Microbial activity oxidizes the organic content in the effluent, removing fine solids, forming sludge, and producing an effluent with less organic solids.
The activated sludge process involves the addition of a mixture of active microorganisms to sewage, followed by aeration and agitation. Aerobic conditions and microbial activity cause the organic materials to coagulate, flocculate, and settle. Activated sludge yields a clear liquid with no bad odor.
Tertiary Treatment
The wastewater is then subjected to tertiary treatment/disinfection, which involves the use of UV radiation or chlorine. Other technologies, including as sand filters and reverse osmosis, may be employed instead of this step of treatment, depending on the type of the sewage and secondary treatment effluent.
Sludge Treatment and Disposal:
Anaerobic digestion, dewatering, and drying are used to treat and stabilize sludge formed throughout the process before it is disposed of or used for beneficial purposes.