Question

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

Answer 1

Hint: Sewage is waste water released from homes and contains disease causing organisms.

Step by step solution
Sewage is defined as the waste-water commonly released from homes and industries. It consists of various types of waste material which can be solid waste or liquid waste. This waste is responsible for contaminating and polluting sea and river water, if not treated properly. Hence, the sewage water is treated by a series of procedures for its purification to be used again.
Untreated sewage water if discharged into river and seas, leads to the following conditions-
First, the sewage water consists of a big mass of solid wastes, primarily plastics. These plastics not only cause water pollution but also take billions of years to degrade biologically. Hence, they pose a major threat for the environment.
Secondly, the untreated sewage water also contains oxygen consuming microorganisms. This increases competition for survival and aquatic animals which primarily depend on the dissolved oxygen are adversely affected.
Also, the untreated sewage water consists of bacteria such as E. coli and other harmful bacteria which causes water borne diseases such as chlorella, dysentery and typhoid in humans. Hence, the sewage water should be treated before discharging them to the water bodies.

Additional information: The sewage treatment plant consists of three stages, mainly primary treatment, secondary treatment and the tertiary treatment. In the primary treatment, the waste water is introduced to large sedimentation tanks in which the large particles are removed. In the secondary treatment, the process of active sludge formation takes place. Lastly, in the tertiary stage, the process of filtration takes place and pure water is obtained.

Note: Sewage water if not treated can cause some serious water borne diseases. The water which comes in our home is also sewage water which undergoes a series of purification steps before being fit for use. If this water is not treated properly the bacteria present in it can cause some serious diseases.