This set of Biomass Energy Multiple Choice Questions & Answers (MCQs) focuses on “Biogas Production from Waste Biomass”.
1. Which of the following is a substrate for biogas production?
a) Municipal and residential waste
c) Metallic waste
d) Gaseous effluents
Explanation: Municipal and residential waste is a good substrate for biogas production. E-waste and metallic waste do not consist of carbon compounds. Gaseous effluents are not used to produce biogas.
2. Which of the following is a preferred substrate for biogas production? Note that TS stands for total solids.
a) Less than 1% TS
b) 20-40% TS
c) 1-5% TS
d) 5-10% TS
Explanation: 20-40% TS is a preferred substrate for biogas production. It is the solid waste in the incoming municipal and residential waste and hence is also called as solid waste.
3. What are the categories for organic dry matter on the basis of total solids (TS)?
a) Low grade, medium grade, high grade and fixed bed
b) Low grade, medium grade, fluidized bed and fixed bed
c) Low grade, medium grade, high grade and solids
d) Downdraft, circulation fluidized bed, high grade and fixed bed
Explanation: The categorization on the basis of TS are low grade with less than 1%, medium grade with TS between 1and 5%, high grade with TS between 5 and 20% and finally solids with TS between 20 and 40%. Fixed bed and fluidized bed are types of gasifiers.
4. Which among the following is the best source for methane production?
a) Metallic scrap
c) Plastic waste
d) Water hyacinth
Explanation: Water hyacinth is the best source for methane production in the given options. It is an aquatic weed with huge biomass, high C/N ratio and lignin content. Thus, yielding high amounts of methane.
5. Which of the following is used to produce biogas from biomass?
a) Anaerobic treatment
b) Aerobic treatment
Explanation: Anaerobic treatment of municipal and residential waste is used to produce biomass. Fermentation is used to produce ethanol and pyrolysis is used to produce gaseous products like hydrogen.
6. Which of the following best indicates the steps of anaerobic digestion?
a) Waste water feed → biogas storage → generator → biogas
b) Waste water feed → digester → biogas → biogas storage → generator
c) Generator → waste water feed → digester → biogas → biogas storage
d) Waste water feed → biogas → digester → biogas storage → generator
Explanation: Waste water feed is first sent into the anaerobic digester. The waste water is treated to produce biogas which is then stored in a special storage. The fuel is then used to produce electricity by driving a generator or for any other application.
7. Which of the following best indicates the steps inside an anaerobic digester?
a) Hydrolysis → methanogenesis → acetogenesis → acidogenesis
b) Hydrolysis → acidogenesis → methanogenesis → acetogenesis
c) Hydrolysis → acidogenesis → acetogenesis → methanogenesis
d) Methanogenesis → acidogenesis → acetogenesis → hydrolysis
Explanation: The waste is first hydrolyzed and then acidized. After acidizing, the product is then used to produce acetates which is further used to create methane in the final stage. Methanogenesis is the process of creating methane.
8. What occurs in the hydrolysis step of anaerobic digestion?
a) Large polymers combine with water molecules
b) Large polymers break down to form water molecules
c) Small polymers combine to form large polymers with the help of water molecules
d) Large polymers break down into amino acids, fatty acids and simple sugars
Explanation: Hydrolysis is used to break large polymers in the presence of an acid catalyst. Large polymers present in the waste break down into amino acids, fatty acids and simple sugars.
9. Acidogenesis further break down the molecules received from hydrolysis in anaerobic digestion.
Explanation: In acidogenesis, microorganisms further break down the molecules after hydrolysis. This is because these molecules are still too large and cannot be used to generate methane. The microorganisms produce an acidic environment for the break down to occur.
10. Which of the following is produced in acetogenesis?
Explanation: In acetogenesis, a derivative of acetic acid called acetate is produced from carbon and other energy sources. This occurs in the presence of microorganisms called acetogens.
11. Which of the following is produced apart from acetates in acetogenesis step in anaerobic digestion?
a) Carbon monoxide
c) Carbon dioxide
Explanation: Apart from acetates, carbon dioxide and hydrogen are also produced in acetogenesis. It is important to note that acetic acid is first produced which is then converted into acetates.
12. What are the two ways to produce methane in methanogenesis step?
a) Converting carbon monoxide and carbon dioxide into methane
b) Converting carbon monoxide and acetic acid (or acetate) into methane
c) Converting methane into carbon monoxide and carbon dioxide
d) Converting carbon dioxide and acetic acid (or acetate) into methane
Explanation: Methanogenesis is the process of producing methane by methanogens. In anaerobic digestion, methanogenesis occurs by converting carbon dioxide and acetic acid (or acetate) into methane.
13. Methanogens can directly use the products of hydrolysis to produce methane.
Explanation: Methanogens cannot directly use the products of hydrolysis to produce methane. The molecules are still too large and need to be broken down. This occurs in the acidogenesis step.
14. What are the two main products of anaerobic digestion?
a) Carbon monoxide and hydrogen
b) Methane and carbon dioxide
c) Methane and carbon monoxide
d) Hydrogen and carbon dioxide
Explanation: The purpose of anaerobic digestion is to convert the municipal waste (biomass) into biogas. So, the two main products are methane and carbon dioxide. Carbon monoxide is not the main product.
15. Gases emitted from the digester indicates the amount of biomass left to be broken down.
Explanation: Gases emitted from the digester indicates the amount of biomass left to be broken down. Production levels are a good indication of production abnormalities and hence this technique is widely used in industries.
Sanfoundry Global Education & Learning Series – Biomass Energy.
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