NCERT 7th Class (CBSE) Science: Wastewater Management

Question: What are the alternate arrangements for sewage disposal?

Answer: To improve sanitation, low cost onsite sewage disposal systems are being encouraged. These are:

1. Septic tanks,
2. Chemical toilets
3. Composting pits, and
4. Vermi-processing toilets.

Question: How sewage is classified based on colour and smell?

Answer: Based on odour and colour, sewage is classified as:

1. Sullage water: Waste water released from the kitchen is called sullage water.
2. Foul waste: Waste water released from toilets is termed as foul waste. It is full of germs and microbes and is highly infectious.
3. Trade waste: Waste from factories and industries. Contains chemicals and are toxic in nature.

Question: What is the function of skimmer in waste water treatment plant?

Answer: The skimmer removes the floating solids like oil and grease.

Question: How sludge is decomposed?

Answer: Sludge is decomposed by the action of anaerobic bacteria. During this process biogas is produced which is used as fuel or can be used to produce electricity.

Question: Why is vermi-compost considered as rich source of nutrients?

Answer: Vermi-compost consist of organic matter which is prepared by the action of earthworms on human or animal waste. It is in nutrients and is a good source of manure.

Question: Why it is suggested to grow eucalyptus trees all along sewage ponds?

Answer: Eucalyptus trees absorb all surplus wastewater rapidly and release pure water vapour into the atmosphere.