What is sewage? How it produced?

What is sewage ? How is sewage disposed of ?

What are electromagnetic waves? How are they produced?

What is popularly known as 'A smile in the sky' ? How is it produced ?

What is meant by magnetic field? How is it produced?

In anaerobic sludge digestion, during secondary treatment of sewage, biogas is produced which is a mixture of :

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

What is sound and how is it produced ?

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