Question
Which of the following in sewage treatment removes suspended solids ? [NEET 2017]
(a) Tertiary treatment
(b) Secondary treatment
(c) Primary treatment
(d) Sludge treatment
Answer/Explanation
Ans. (c)
In sewage treatment, suspended solids are removed during primary treatment. It is also known as physical treatment.
It consists of shredding, churning, screening and sedimentation.
Sequential filtration removes floating and large suspended solids.
Question
Biochemical Oxygen Demand (BOD) may not be a good index for pollution in water bodies receiving effluents from [NEET 2016, Phase II]
(a) domestic sewage
(b) dairy industry
(c) petroleum industry
(d) sugar industry
Answer/Explanation
Ans. (c)
Biochemical Oxygen Demand (BOD) is not a good index for checking the pollution levels of water bodies receiving effluents from petroleum industry. This is because such effluents contain waste which is non-biodegradable.
Question
What gases are produced in anaerobic sludge digesters? [CBSE AIPMT 2014]
(a) Methane and $\mathrm{CO}_2$ only
(b) Methane, hydrogen sulphide and $\mathrm{CO}_2$
(c) Methane, hydrogen sulphide and $\mathrm{CO}_2$
(d) Hydrogen sulphide and $\mathrm{CO}_2$
Answer/Explanation
Ans. (b)
Methane, hydrogen sulphide and $\mathrm{CO}_2$ are gases that are produced in anaerobic sludge digesters. These gases are produced during biogas production by the activity of bacteria called methanogens.
Question
During sewage treatment, biogases are produced, which include [NEET 2013]
(a) methane, hydrogen sulphide and carbon dioxide
(b) methane, oxygen and hydrogen sulphide
(c) hydrogen sulphide, methane and sulphur dioxide
(d) hydrogen sulphide, nitrogen and methane
Answer/Explanation
Ans. (a)
During sewage treatment biogas is produced which include methane, hydrogen sulphide and carbon dioxide. Biogas is a mixture of gases (mainly methane) produced by the microbial activity and which may be used as fuel.
Question
Which of the following is mainly produced by the activity of anaerobic bacteria on sewage? [CBSE AIPMT 2011]
(a) Propane
(b) Mustard gas
(c) Marsh gas
(d) Laughing gas
Answer/Explanation
Ans. (c)
Marsh gas (methane) is mainly produced by the activity of anaerobic bacteria on sewage.
Question
Organisms called methanogens are most abundant in a [CBSE AIPMT 2011]
(a) cattle yard
(b) polluted stream
(c) hot spring
(d) sulphur rock
Answer/Explanation
Ans. (a)
Organisms called Methanogens are most abundant in a cattle yard. Methanogens are present in the gut of several ruminants animals such as cows and buffaloes and they are responsible for the production of methane (biogas) from the dung of these animals.
Question
Secondary sewage treatment is mainly a [CBSE AIPMT 2011]
(a) mechanical process
(b) chemical process
(c) biological process
(d) physical process
Answer/Explanation
Ans. (c)
In secondary or biological treatment of municipal waste, the organic matter is decomposed with the help of microbes. Decomposition of organic matter occurs by one of the three methods-water hyacinth pond, trickling filter method and activated sludge method. After decomposition the treated water is sterilised through chlorination and recycled.
Question
Select the correct statement from the following [CBSE AIPMT 2010]
(a) Biogas is produced by the activity of aerobic bacteria on animal waste
(b) Methanobacterium is an aerobic bacterium found in rumen of cattle
(c) Biogas, commonly called gobar gas, is pure methane
(d) Activated sludge-sediment in settlement tanks of sewage treatment plant is a right source of aerobic bacteria
Answer/Explanation
Ans. (d)
Out of the following statements (d) is correct because activated sludge is a process dealing with the treatment of sewage and industrial waste waters. Atmospheric air or pure oxygen is introduced to a mixture of primary treated or screened sewage (or industrial waste water) combined with organisms to develop a biological flock, which reduces the organic content of the sewage. Sediment in settlement tanks of sewage treatment plant is a rich source of aerobic bacteria because small amounts are used as inoculum in secondary treatment or biological treatment stage of sewage treatment.
Question
Which one of the following is being utilised as a source of bio-diesel in the Indian countryside? [CBSE AIPMT 2007]
(a) Euphorbia
(b) Beet root
(c) Sugarcane
(d) Pongamia
Answer/Explanation
Ans. (a)
Euphorbia is being utilised as a source of biodiesel in the Indian countryside. Some plants like Euphorbia, Asclepias, Capiafera accumulate hydrocarbons in the form of latex which are used as biodiesel.
Question
During anaerobic digestion of organic waste, such as in producing biogas, which one of the following is left undegraded? [CBSE AIPMT 2003]
(a) Hemicellulose
(b) Cellulose
(c) Lipids
(d) Lignin
Answer/Explanation
Ans. (d)
During biogas formation, digestion ofcellulose is slow (rate-limiting) and most of the lignin is not decomposed. After cellulose lignin is the most abundant plant polymer. It forms 20 to 30% of the
wood of the tree. Lignin is a complex polymeric molecule, made up of phenyl propanoid units. Cellulose is a large chained polymer of glucose molecules which are linked with each other by
glycosidic bonds. Hemicellulose are branched polymers of glucose, xylose, galactose, mannose and arabinose.