By-product Utilisation Questions and Answers

Answer: A

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. Bagasse arises at about 30 per cent of the cane crushed, so a mill taking 3000 tonnes a day produces some 900 tonnes of fuel a day.

That is more than enough for the mill's own steam and electrical demand, and modern mills with high-pressure boilers export the surplus power to the grid. The arrangement is unusually favourable: the fuel arises continuously, at the point of use, in step with the demand it serves.

Answer: B

Correct answer: Statement I is incorrect but Statement II is correct

Statement I is incorrect: molasses needs very little preparation, only dilution to a suitable sugar concentration and adjustment of pH and nutrients.

Statement II is correct and is exactly why. The sugars in molasses are sucrose, glucose and fructose - already in a form yeast can take up and ferment. Contrast lignocellulose, which requires a pretreatment to open the lignin barrier and then an enzymatic hydrolysis before any fermentation can begin; that difference is what has kept molasses the cheaper feedstock.

Answer: C

Correct answer: 2, 1, 4, 3

The order is fixed by what each step needs from the last. Pretreatment comes first (2) to open the lignin barrier, since without it the enzymes cannot reach the cellulose at all.

Enzymatic hydrolysis then releases fermentable sugars (1), the yeast ferments them to ethanol (4), and distillation with dehydration recovers and dries the product (3). The first two steps are what distinguish this route from molasses fermentation, and they are the reason it costs so much more.

Answer: D

Correct answer: 2, 1, 4, 3

The sequence begins at the mill, where the husk is collected and cleaned (2) - soil and grit would contaminate the ash and dilute the silica.

It is then burnt under controlled conditions below about 700 degrees (1), which is the critical step, since a higher temperature crystallises the silica and destroys the pozzolanic activity. The amorphous ash is recovered from the furnace (4) and finally ground to the required fineness (3), because reactivity depends on surface area as well as on being amorphous.

Answer: A

Correct answer: 2, 4, 1, 3

The peel is first washed and dried (2), removing sugars and other solubles that would otherwise contaminate the product. It is then extracted with hot dilute acid (4), which hydrolyses the protopectin holding the pectin in the cell wall and brings it into solution.

The pectin is precipitated from that solution with alcohol (1), since it is insoluble in alcohol while the impurities remain dissolved, and the precipitate is finally dried and milled (3) to a standardised powder.

Answer: B

Correct answer: 1, 2, 3, 4

The chain runs from a physical property to an economic outcome. Loose residue has a very low bulk density (1), so a lorry reaches its volume limit long before its weight limit (2) and carries only a fraction of the tonnage it could.

Compaction raises the density several fold (3) - for husk, from about 100 to 650 kg/m\(^3\) - so the same lorry now carries several times the mass. Transport cost per tonne falls accordingly and distant use becomes viable (4). The briquetting energy is the price paid for that.

Answer: C

Correct answer: 1, 2, 3, 4

Complexity rises through the list. Direct combustion (1) needs only a furnace. Briquetting before combustion (2) adds a compaction step with its own energy and equipment cost.

Anaerobic digestion (3) requires a sealed digester, temperature control, retention times measured in weeks and management of a living microbial population. Pretreatment with enzymatic hydrolysis to ethanol (4) is the most demanding of all, needing two conversion stages before fermentation can even begin, plus distillation afterwards.

Answer: D

Correct answer: Only three

Three pairs are right. Rice husk yields boiler fuel and pozzolanic ash; rice bran yields edible oil and a defatted feed; molasses yields ethanol and a feed supplement.

The fourth is wrong. Bagasse is the fibrous residue left after cane is crushed, and it is used as boiler fuel, for paper and board, and as a feedstock for particle board - not for pectin. Pectin comes from citrus peel and apple pomace, where the cell walls are rich in it.

Answer: A

Correct answer: Only three

Three pairs are right. Anaerobic digestion yields biogas together with a digestate useful as fertiliser; gasification yields producer gas; and fermenting molasses yields ethanol.

The fourth is wrong. Briquetting compacts the material without changing its chemistry, so the calorific value per kilogram is essentially unaltered. What rises is the value per cubic metre, and that is precisely the point - the problem being solved is one of volume, not of energy content.

Answer: B

Correct answer: Only three

Three pairs are right. Rice husk ash is valuable for its amorphous silica, oilseed cake for its protein, and wheat bran for its dietary fibre.

The fourth is wrong. Bagasse is almost entirely lignocellulosic fibre with very little protein, which is why it is burnt or made into board rather than fed. Its value lies in its bulk and its energy content, and in the fact that it arises at the mill in exactly the quantity the mill's boilers can use.