हिंदी
CISCEISC (Science) ISC Class 12
प्रश्न पत्र३७४
पाठ्यपुस्तक उत्तर१४३३३
महत्वपूर्ण प्रश्न एवं उत्तर६१५२
अवधारणा स्पष्टीकरण और वीडियो८९९
समय सारणी१६
पाठ्यक्रम

Microbes in Sewage Treatment - Treatment of Sewage

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Estimated time: 11 minutes

Sewage Treatment

CISCE: Class 12

1. Primary Treatment (Physical Process)

  • This initial step involves the physical removal of particles from the sewage through filtration and sedimentation.
  • First, floating debris is removed using a process called sequential filtration.
  • Next, grit, which consists of soil and small pebbles, is removed through sedimentation.
  • All the solid materials that settle to the bottom form the primary sludge.
  • The liquid portion that remains on top, known as the supernatant, forms the effluent.
  • This effluent is then taken forward for secondary treatment.
CISCE: Class 12

2. Secondary or Biological Treatment

  • The primary effluent is moved into large aeration tanks where it is constantly mechanically agitated.
  • Air is continuously pumped into these tanks.
  • This environment promotes the vigorous growth of useful aerobic microbes into structures called "flocs", which are masses of bacteria and fungal mycelium.
  • These microbes consume the majority of the organic matter present in the effluent.
  • This consumption significantly reduces the Biochemical Oxygen Demand (BOD) level of the effluent.
  • Once the BOD is significantly reduced, the effluent is passed into a settling tank where the bacterial flocs are allowed to sediment.
  • The resulting sediment of bacterial flocs is called activated sludge.
  • This activated sludge is then pumped into large tanks called anaerobic sludge digesters.
  • During digestion in these tanks, a mixture of gases is produced, including methane (CH₄), hydrogen sulphide (H₂S), and carbon dioxide (CO₂).
  • These gases collectively form biogas, which can be utilised as a source of energy.
  • Finally, the treated effluent from the settling tank is safely released into natural water bodies, such as rivers and streams.
CISCE: Class 12

BOD

  • BOD stands for Biochemical Oxygen Demand, which is a measure of the organic matter present in water.
  • The greater the BOD of wastewater, the higher its potential for causing pollution.
CISCE: Class 12

Key Points: Microbes in Sewage Treatment

  • Sewage treatment is carried out in two stages: primary treatment and secondary (biological) treatment.
  • Primary treatment involves physical removal of floating debris by filtration and heavy particles by sedimentation, forming primary sludge and effluent.
  • In secondary treatment, the effluent is aerated in large tanks to promote growth of aerobic microbes that consume organic matter.
  • Microbial activity reduces the BOD (Biochemical Oxygen Demand), thereby decreasing the polluting potential of sewage.
  • The settled activated sludge is digested anaerobically to produce biogas, and the treated effluent is released into natural water bodies.
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