Revison (waste To Energy Technologies)

Question 1

2017 Q1(a): Describe the concept of embodied energy.

Answer 1

Embodied energy is the total energy required to manufacture and produced any material, resource or service.

Question 2

2015 Q7: The figure below shows a schematic diagram of a typical waste to energy plant. Discuss the advantages and disadvantages of recovering energy from waste by incineration. Your answer should make specific reference to the following issues associated with energy recovery from waste incineration.

Environmental issues.
Economic issues.
Security of supply issues.

Answer 2

Environmental issues;
In the eyes of the public incinerators are generally seen as an extremely dirty way of disposing of waste and they think it should only be used as a last resort. Although incineration can help with the landfill issue as it cuts down on the amount of waste sent to landfill by about 90%. Emissions given off by incineration can be negated by filtering, also known as scrubbing.

Economic issues;
Businesses will have to pay less landfill tax if energy is produced from waste from incineration. On top of this the ash produced from incineration may be able to be used in some building materials. Incineration may also be used to produce energy to power communities, however due to the fact that incinerators cost so much to build and develop its usage would have to justify the high price tag.

Security of Supply Issues;
Incinerators run the risk of becoming low on supply due to the fact that waste could be exported to other countries that would charge lower gate fees, and the fact that there could also be some illegal activity with the gates fees. This would be problematic as to be feasible project incinerators need a secure supply of waste to burn.

Question 3

2016 Q1 (a): Explain the following key terms with anaerobic digestion

Answer 3

Low solids;
This is when the feedstock is approx 15% solid.

High solids;
This is when the feedstock is approx 55% percent.

Residence time;
This is the time that it takes for a substance to be fully digested in an digestion system.

Single-stage;
This is when the digestion takes place in only one single tank.

Multi-stage;
This is when the digestion takes place in many different tanks.

Question 4

Spec paper Q2(b): The diversion of biodegration waste to anaerobic digestion can reduce greenhouse gas emissions from landfill.

For example e.g capturing the biogas from one tonne of food waste will save between 0.5 and 1.0 tonne of CO2 equivalent.

Explain how anaerobic digestion results in the production of biogas.

Answer 4

Hydrolysis - insoluble polymers broken down to soluble organic compounds.

Acidogenesis - alcohols and fatty acids converted into acetic acid and hydrogen.

Methanogensis - bacteria convert acetic acid and hydrogen into methane and carbon dioxide / biogas.

Question 5

2017 Paper Q1 (b). In figure 1 below identify A and B in the stages associated with anaerobic digestion.

Answer 5

A: hydrolysis
B: acetogenesis

Question 6

Spec paper Q2(b)(ii) Outline how anaerobic digestion can deliver both heat and power.

Answer 6

Biogas from an AD plant can be burnt in a combined CHP plant, this generates power (electricity) and heat.

Instead of losing hte heat, as in traditional power plants, it is diverted into a local heating system.

Question 7

2016 Q1(b), outline how anaerobic digestion can be used to provide both heat and power (CHP)

Answer 7

Biogas from the AD plant can be burnt in a CHP plant to generate power (electricity) and heat; instead of losing heat, as in a traditional power plant, it is diverted into local heating systems.

Question 8

2016 Q1(c) Home composting is encouraged by many local councils. Name three types of waste products which can be composted in a domestic situation.

Answer 8

Any three from;
- Lawn clippings
- Shredded stalks
- Vegetable peelings
- Hedge clippings
- Cut flowers
- Tea bags
- Leaves
- Eggshells

Question 9

2016 Q1 (d); Explain briefly why composting is unsuitable for treating any form of catering waste.

Answer 9

Cooked food must never be used in composting it will attract vermin.

Question 10

Spec patter Q4(a). Define what is meant by bioremediation and state two pollutants that can be treated using this technology.

Answer 10

Bioremediation - the use of microorganisms in the treatment of environmental pollution / waste.

Any two pollutants from:

• oil spills
• chlorinated pesticides
• heavy metals
• diesel oil
• PCBs