Section outline

    • Important terms:

      1. Wastewater is the dirty water that goes down the drains from sinks, showers, toilets, laundries, etc.

      2. Cleaning of water is a process of removing pollutants from the wastewater at a wastewater treatment plant before it enters a water body or is reused. 

      3. Sewage treatment is the process of wastewater treatment.

      4. Sewage is a complex liquid waste containing suspended solids, organic & inorganic impurities, nutrients, saprophytes & disease-causing bacteria & other microbes.

      5. Sewers are big or small pipes that carry wastewater.

      6. Sewerage is a network of sewers that carries sewage from the point where it is produced to the point of disposal, i.e. treatment plant.

      7. Sludge is the solid waste & impurities collected from the wastewater during the treatment in a wastewater treatment plant. 

      8. Vermi-processing toilet is a toilet where human excreta is treated by earthworms & converted to vermi cakes which are used as manure.

      Key Points:

      1. UN declared - International Decade for action on “Water for life” as 2005–2015

      2. World Water Day - 22 March

      3.  In 2016,  Government of India has initiated “Swachh Bharat".

      4. Activated sludge contains 97% water.

      5. Biogas is used as fuel & to generate electricity.

      6. Poor sanitation and contaminated drinking water is the cause of a large number of diseases.

    • 1. Constituents of Sewage:

      2. Steps of cleaning water in a wastewater treatment plant:

       

       

    • Quick revisions notes

      1. Sources of wastewater / sewage are:

      • Housholds, industries, hospitals, offices & other users. 
      • Rainwater during a storm or heavy rains.

      2. Manholes are located:

      • Every 50 m to 60 m.
      • Junction of two or more sewers.
      • Change in direction of sewers.

      3. At wastewater treatment plant:

      • Bar screens - large objects (rags, sticks, cans, plastic packets, napkins) removed.
      • Grit & sand removal tank - sand, grit & pebbles settle down.
      • Clarifier Tank - Sludge (solid impurities & feaces) settle down. Skimmer removes the floatable solids like oil & grease & clarified water obtained. Sludge is decomposed by anaerobic bacteria to form biogas in a separate tank.
      • Aeration - Aerator pumps air into clarified water to help aerobic bacteria to grow. Activated sludge settles down. Water is removed by sand drying beds or machines & activated sludge is dried & used as manure.
      • Disinfection - water maybe disinfected using chlorine or ozone before letting into water bodies.

      4. Disposing waste in drains causes:

      • Fats & oil - block & harden pipes & clog soil pores.
      • Chemicals - kill microbes that purify water.
      • Solid waste - choke the pipe & don't allow free flow of oxygen.

      5. Vermi-processing toilet:

      • Earthworms convert human excreta to vermi cakes which are used as manure.
      • Safe, hygienic, environment friendly & low water use toilet.

      6. Untreated human excreta:

      • Causes soil & surface & ground water pollution.
      • Becoming a source of many water borne diseases like cholera, typhoid, polio, meningitis, hepatitis and dysentery.

      7. Untreated sewage:

      • Causes & spreads water borne diseases like cholera, dysentery & typhoid.
      • Pollutes & contaminates rivers, lakes, and other water bodies, making them unsafe for use. 
      • Harms aquatic life in rivers & oceans.
      • Degrades soil quality & harms the plants.

      8. Onsite methods of sewage disposal:

      • Septic tanks
      • Chemical toilets 
      • Composting pits. 

      9. Use of septic tanks:

      • No sewerage system.
      • Hospitals
      • Isolated buildings or a cluster of 4 to 5 houses.

      10. Eucalyptus trees:

      • Plant along sewage ponds.
      • They absorb all surplus wastewater & release pure water vapour into the atmosphere.