What is Sewage?
Sewage comprises waste water generated from households, hotels and may include industrial waste water.
What type of waste does sewage contain?
Sewage usually contains a high quantity of organic wastes and may also consist of inorganic wastes. It is essential to treat sewage before its entry into any water body. Why so? Sewage, if allowed to enter water sources without treatment, it will contaminate them; which is why it is essential to treat sewage properly before letting it into rivers or streams for example.
“We Offer Services in ETP Operations and maintenance"
Sewage Treatment Plant process
Sewage can be treated by designing a sewage treatment plant (STP) which involves three stages: primary/preliminary, secondary and tertiary.
Primary Treatment
Sewage treatment plant process
In a sewage treatment plant, sewage water is first allowed to pass through screens or grit chamber where large solids are removed. This step is followed by aeration/mixing in a tank and then primary sedimentation where suspended solids settle down. Primary treatment involves addition of a coagulant and aims at removing grits, coarse solids, oil and grease if any present. Preliminary treatment results in sedimentation of solids (sludge) and formation of an effluent that floats above sludge. Effluent from primary treatment consists of 45-50 % unstable organic matter. The effluent then undergoes secondary treatment where fine solids settle out by means of bacterial activities.
"We offer Services in ETP Design"
Secondary or Biological Treatment
This stage converts organic matter in sewage into stable forms through biological activities, resulting in secondary sedimentation. Common approaches are trickling filters and activated sludge method.
Trickling filters comprise an enclosed tank with a bed of bricks and a layer of microorganisms. The effluent enters the tank through an inlet and trickles over the bed layer by sprinklers. Microbial activities oxidize the organic matter in the effluent, resulting in the removal of fine solids, formation of sludge and an effluent with less organic solids.
Activated sludge method involves the addition of a mixture of active microorganisms to sewage, followed by aeration and agitation. The aerobic conditions and microbial actions oxidize the organic solids resulting in coagulation, flocculation and settling of solids. Activated sludge produces a clear liquid without foul odor.
Secondary treatment is divided into two different treatment processes:
1. Aerobic Treatment – Aerobic wastewater treatment is a biological treatment that uses oxygen to break down organic matter and remove other pollutants like nitrogen and phosphorus. Generally, in the sewage treatment, aerobic treatment is performed.
2. Anaerobic Treatment – Anaerobic treatment is a process where wastewater or material is broken down by micro-organisms without the aid of dissolved oxygen. However, anaerobic bacteria can and will use oxygen that is found in the oxides introduced into the system or they can obtain it from organic material within the wastewater.
Leave A Comment