Class 7 Science Chapter 13 MCQ

The used water should not be wasted. Use water or waste water could be reduced after cleaning it. We must clean the used water by removing various impurities from it, before it is re-used or released into the environment (such as river, lakes sea or ground).

Sewage is mainly a liquid waste. The waste water and faeces from homes and other buildings which is carried away in sewers, called sewage.

Biogas and sludge both are the products of wastewater treatment.

Here, all the statements are correct. Hence, your answer will be option [D].

Sewage is a liquid waste which causes water pollution as well as soil pollution.

Asthma is not a water-borne disease. It is caused by polluted air.

Chlorine is the chemical used as water disinfectant.

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Phosphate is an inorganic impurity of the sewage.

Here, all the statements are correct. Hence, your answer will be option [D].

In a filtration plant, water is filtered using layers of sand, fine gravel and medium gravel.

In the that processing toilet, the human excreta is treated by earthworms in a pit not by cockroaches and round worms. The earthworms gradually eat up all the organic matter present in human excreta, decompose it and pass out from their body in the form of worm casting also called vermi-cakes.

Here, all the statements are correct. Hence, your answer will be option [D].

It may be necessary to disinfect the treated water with chemicals like chlorine or ozone before releasing it into the distribution system. The ozone layer is a thin part of the Earth’s atmosphere that absorbs almost all of the sun’s harmful ultraviolet light or rays.

UNICEF said that a lack of access to clean water causes waterborne illnesses that kill more than 1.6 million young children each year. Lack of separate and decent sanitation facilities at schools often forces girls to drop out of primary school. Of the 120 million school-age children not in school, the majority are girls. Millions of children suffer intestinal infections caused by parasites. Each year 19.5 million people are infected with roundworm and whipworm alone, with the highest rate of infection among school-age children. Also, each year, an estimated 118.9 million children under 15 suffer from schistosomiasis (bilharzia), a disease caused by parasitic flatworms. Parasites consume nutrients, aggravate malnutrition, retard children’s physical development and result in poor school attendance and performance. “By providing clean water and sanitation to the poorest people on the planet, we can reduce poverty and suffering and ensure education for all children” – UNICEF.

We know that the solid part of sewage is called sludge. The sludge is taken out from the bottom of first sedimentation tank and put into a large, close tank called the digester tank. In the digester tank, many types of “anaerobic bacteria” decompose the organic matter present in the sludge to produce biogas also called sewage gas.

Here, all the statements are correct. Hence, your answer will be option [D].

Sometimes, it may be necessary to disinfect the treated water with chemicals like chlorine or ozone before releasing it into the distribution system. The purpose of disinfection in the treatment of wastewater is to eliminate completely the harmful micro-organisms in the water to be discharged back into the environment.

Here, all the statements are correct. Hence, your answer will be option [D].

The biogas produced is used as a fuel. The human waste or human excreta can be used in a biogas plant along with cow dung for making biogas. So, in many villages, human excreta from the toilet seats in the homes flows directly into biogas plant through covered drains.

Here, all the statements are correct. Hence, your answer will be option [D].

The generation of waste is an essential part of human activities. But we can limit the type of waste and quality of waste produced. We can also help in the proper disposal of waste. It is the responsibility of the Municipality of the area to maintain sanitization at public places but we can also contribute in this effort. All of us have a role to play in keeping our environment clean and healthy. Adopting good sanitization practices should become our way of life. It will keep all of a healthy and happy.

The aeroplanes have a special type of toilet called “vacuum toilets”. So, the human excreta or sewage in an aeroplane is disposed of through vacuum toilets. When we flush the toilet in an aeroplane, then a valve opens in a pipeline which has vacuum inside it. The vacuum in the pipeline sucks the human excreta from the toilet seat with a great force making a loud noise and carries it into a tank on board the aeroplane. When the aeroplane lands at an airport, then the tank containing all the human excreta is emptied into a sewer line into the ground through connecting pipes.

Here, all the statements are correct. Hence, your answer will be option [D].