Sewage Treatment Plant
Sewage treatment plant is used to treat wastewater from residential, commercial and industrial areas. STP Plant has become very important in today's time. Using this process, sewage is treated, and the contaminated water is prepared for reuse. A sewage treatment plant is useful not only for protecting the environment but also for water conservation. Treated water can be reused for irrigation, industrial cooling and flushing systems.
There are different stages of treatment in a STP plant - preliminary, primary, secondary and tertiary. Large particles are removed in the preliminary stage. Solids and liquids are separated in the primary stage. In secondary treatment, organic matter is degraded using biological processes. In the tertiary stage, advanced techniques like membrane filtration and UV disinfection are used so that water is purified as per environmental standards.
In today's urban areas, STP plant is an effective solution to reduce pollution, save water resources and promote sustainable development.
Sewage Treatment Plant Process
Sewage can be treated by designing a three-stage sewage treatment plant (STP): primary/preliminary, secondary, and tertiary.
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Primary Treatment- Sewage Water is first permitted to travel through screens or grit chambers in a sewage treatment facility, where big solids are removed. This is followed by tank aeration/mixing and primary sedimentation, in which suspended solids settle. The addition of a coagulant is used in primary treatment to remove grits, coarse particles, oil, and grease, if present. Preliminary treatment results in solids (sludge) sedimentation and the creation of an effluent that floats above the sludge. Primary treatment effluent contains 45-50% unstable organic materials. The wastewater is subsequently subjected to secondary treatment, in which fine particulates settle out due to bacterial activity.
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Secondary or Biological Treatment- Through biological processes, this stage transforms organic waste in sewage into stable forms, resulting in secondary sedimentation. Trickling filters and the activated sludge technique are two common approaches.
Trickling filters are made up of 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. Microbial activities oxidise the organic matter in the effluent, resulting in the removal of fine fines, the production of sludge, and a lower organic solids content in the effluent.
The activated sludge process involves adding an active microbe mixture to sewage, followed by aeration and agitation. Aerobic conditions and microbial activity oxidise organic materials, causing coagulation, flocculation, and solid settling. Activated sludge yields a clear liquid with no odour. -
Tertiary Treatment –The wastewater is subsequently subjected to tertiary treatment/disinfection via the use of UV radiation or chlorination. Depending on the nature of the sewage and the effluent from secondary treatment, other technologies such as sand filters and reverse osmosis may be employed instead at this step of treatment.
