Biomass Energy Questions and Answers

Answer: A

Biofuels are derived from renewable sources.

Biofuels such as ethanol, biodiesel and biogas are made from plant or animal biomass that can be grown again, so the carbon they release was recently taken from the air. Fossil fuels come from ancient biomass that will not be replaced on any human time scale.

Biofuels generally have a lower energy density than petrol or diesel. Extra refining and higher cost per unit of energy are not what defines them, and need not be true.

Answer: D

The process is biomethanation of organic waste.

Biomethanation is anaerobic digestion of organic matter to biogas. It proceeds in four phases: hydrolysis breaks polymers into simple sugars, amino acids and fatty acids; acidogenesis turns them into volatile fatty acids; acetogenesis converts these to acetic acid, hydrogen and CO₂; and methanogenic archaea finally produce methane.

Bioleaching (printed 'Bioleading') uses microbes to extract metals from ores, bioreduction is a microbial reduction reaction, and biomineralisation is the formation of minerals by organisms.

Answer: C

The downstream processing of ethanol from a fermentation broth is done by distillation, which separates ethanol from water because it boils at a lower temperature (about 78 degrees Celsius against 100), and fractional distillation gives about 95 percent ethanol. Filtration only removes cells and solids, flow cytometry is a method for counting and analysing cells, and flame photometry measures sodium, potassium and similar metals, so these three do not recover ethanol. Distillation works here because ethanol has a lower boiling point than water, and the vapour is condensed to give a concentrated product.

Answer: B

The chemical added to a fermenter that uses molasses as the substrate is diammonium phosphate.

Molasses is rich in sugar but poor in nitrogen and phosphorus, which yeast needs for growth, so a nutrient salt supplying both elements is added. Diammonium phosphate supplies ammonium nitrogen and phosphate together, which is why it is the keyed choice. Diammonium sulphate would supply only nitrogen and sulphur, and diammonium nitrate and diammonium chloride would supply nitrogen without any phosphate.

Answer: A

Biogas is a mixture of carbon dioxide, methane, ammonia, hydrogen sulphide and water vapour, produced by the anaerobic breakdown of organic matter, with methane the combustible part.

The other mixtures contain carbon monoxide, nitrous oxide or nitrogen oxides, which are not products of anaerobic digestion in biogas, so they are wrong.

Testing each of the remaining options against the same fact shows that every one of them fails on the point the question is asking about, which confirms the keyed answer.

Answer: A

Gasification is the high temperature conversion of solid carbonaceous fuel into flammable gas.

In gasification a solid fuel such as coal, biomass or waste is heated to about 750 to 850 degrees C or more with a limited supply of oxygen or steam, and it is turned into producer gas, a mixture of carbon monoxide, hydrogen and methane, which burns.

Options (B) and (D) say the product is a liquid, which belongs to liquefaction. The low temperatures of (C) and (D) are too low for gasification reactions.

Answer: B

Biogas produced by anaerobic bacteria is a mixture of CH4, CO2, NH3, H2S and H2O, option (B). Methane is the main fuel gas, usually the larger part, carbon dioxide is the second, and small amounts of ammonia, hydrogen sulphide and water vapour are also present. Option (A) has methanol, which is not a product of biogas, option (C) lists LPG and CO, which are not formed, and option (D) lists SO2 and NO2, which are combustion products and not gases of the digestion.

Answer: B

Fast pyrolysis

Bio-oil is obtained from lignocellulose by fast pyrolysis, heating the biomass rapidly without oxygen and cooling the vapours. Combustion releases heat and gives no oil, gasification gives syngas, and transesterification makes biodiesel from fats and oils.

The other options, Combustion; Gasification; Transesterification, are not the answer to this question. This agrees with the official final answer key for the paper, which gives option B.

Answer: A

Blending of 10 percent biodiesel with 90 percent conventional diesel.

B10 means a blend of 10 percent biodiesel with 90 percent conventional diesel, as the number after B gives the biodiesel share. B90 would be 90 percent biodiesel, and the other options give other shares.

The other options, Blending of 90 percent biodiesel with 10 percent conventional diesel.; Blending of 50 percent biodiesel with 50 percent conventional diesel.; Blending of 1 percent biodiesel with 10 percent conventional diesel., are not the answer to this question. This agrees with the official final answer key for the paper, which gives option A.