Sewage is made up of wastewater produced by homes, hotels, and possibly even factories.To improve the quality of wastewater for recycling, sewage treatment plants use primary, secondary, or biological, and tertiary treatment processes.Waste water is produced as a result of expanding infrastructure development and increased water use for domestic and commercial purposes.
What kind of waste is in sewage?
Sewage typically contains a large amount of organic wastes, though it can also include inorganic wastes. Prior to entering any water body, sewage must be treated. Why so? Because sewage will contaminate water sources if it isn’t properly treated before entering them, such as rivers or streams, it is crucial to treat sewage properly before releasing it.
Process At A Sewage Treatment Plant
A sewage treatment plant (STP) with three stages—primary/preliminary, secondary, and tertiary—can be designed to treat sewage.
- Water from sewage is first allowed to pass through screens in a sewage treatment plant.In a sewage treatment facility, large solids are first removed from the sewage water by passing through screens or a grit chamber. After this, suspended solids settle down during primary sedimentation, which is followed by aeration/mixing in a tank. A coagulant is added as part of the initial treatment, which aims to get rid of any grit, coarse solids, oil, or grease that may be present. Solids (sludge) sediment during preliminary treatment, and an effluent is created that floats on top of the sludge. 45–50% of the primary treatment’s effluent is made up of unstable organic matter. After secondary treatment, the effluent is allowed to settle naturally as a result of bacterial activity.
- This stage uses biological processes to transform sewage’s organic matter into stable forms.In this stage, biological processes transform organic matter in sewage into stable forms, leading to secondary sedimentation. Trickling filters and the activated sludge method are typical strategies.
- An enclosed tank with a brick bed and a layer of microorganisms makes up a trickling filter. Through an inlet, the effluent enters the tank and is sprinkled over the bed layer. The organic matter in the effluent is oxidised by microbial activity, which removes fine solids, creates sludge, and reduces the amount of organic solids in the effluent.
- The process of using activated sludge involves adding a variety of live microorganisms to sewage and then agitating and aerating the mixture. Coagulation, flocculation, and solids settling occur as a result of the aerobic conditions and microbial activity oxidising the organic solids.The liquid that is produced by activated sludge is clear and odourless.
- The effluent is then subjected to tertiary treatment, including UV radiation or chlorination for infection control. Depending on the sewage’s composition and the effluent from secondary treatment, alternative techniques like sand filters and reverse osmosis may also be used for this stage of treatment.
How is the sludge generated by primary and secondary sedimentation used?
Methane (CH4) and carbon dioxide (CO2), which are combustible gases and can be used as fuel, are released as a result of the digestion of sludge in a tank. The digested sludge can be burned off for disposal or applied as fertiliser.