Class 7 Science Chapter 13 MCQ

Water coming out of a laundry is wastewater.

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).

Biogas and sludge both are the products of wastewater treatment.

Open drain system is a breeding place for flies, mosquitoes and organisms which cause diseases.

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.

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

Chlorine is the chemical used as water disinfectant.

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

Phosphate is an inorganic impurity of the sewage.

In the vermi processing toilet, the human excreta is treated by earthworms in a pit.

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

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.

Sewers are not considered as sources of wastewater. Homes, industries and hospitals are considered as a source of waste-water.

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.

We know that sewage is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease-causing bacteria and other microbes. a)Inorganic impurities – Nitrates, Phosphates, metals. b)Organic impurities –Human faeces, animal waste, oil, urea (urine).

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.

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.

The drinking of water contaminated with untreated human excreta becomes the most common route for the spreading of water-borne diseases. Some of the water borne diseases spread in this way are, Cholera, Typhoid, Polio, Meningitis, Hepatitis and Dysentery. Many common infections can spread by airborne transmission are tuberculosis, influenza, small pox etc.

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

It has been suggested that we should plant “eucalyptus trees” all along the sewage ponds. This is because eucalyptus trees absorb all the surplus waste water from the sewage ponds rapidly and release pure water vapor into the atmosphere through transpiration. In this way, eucalyptus tree help in purifying wastewater quite rapidly.

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].

Composting pits are used to provide composting toilets. A composting toilet is a self- contained human waste disposal unit which is not connected to a sewer line or a septic tank. A composting toilet consists of a toilet seat fixed a top a composting chamber which is further connected to a drying chamber. The composting chamber breaks down the human excreta with the help of aerobic microorganisms (such as aerobic bacteria) and converts it into a compost. The composting toilets are used where the water supply is limited or not available at all.