What is sewage ? Explain why it is harmful to discharge untreated sewage into rivers or seas?

What is sewage? In which way can sewage be harmful to us?

What is meant by sewage ?

Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C, but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20mg/L, 8mg/L and 400mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?

What is the use of bar screen at sewage treatment plant?

Raheem tells to his neighbours, "Stagnation of sewage in our surroundings is harmful to our health". Do you support this? Why?

If you are allowed to visit a sewage treatment plant, what doubts you can clarify about the plant from technicians?

Deltas are formed at the points where river enters the sea. Why ?

The discharging current in the atmosphere due to the small conductivity of air is known to be 1800 A on an average over the globe . Why then does the atmosphere not discharge it self completely in due course and becomed electrically neutral ? In other words, what keeps the atmosphere charged?