Waste to energy technologies

Question 1

Define embodied energy

Answer 1

collective sum of all the
energy required to produce any material, product or service

Question 2

Describe what embodied energy is using the example of a brick

Answer 2

Embodied energy is the overall energy needed throughout a products life to make it usable these different stages are seen:
*Energy needed to extract the raw material to make the brick.
*Energy needed to transport the material to manufacturer
*Energy of the processes involved in the manufacture of the brick.
*Energy required for the transport to the building site.
 Energy used in putting the brick into place in the particular application.

Question 3

What are the three measurements of embodied energy

Answer 3

Cradle to grave (whole life)
Cradle to gate (the extraction stage)
Cradle to site (energy used to the point of use of product)

Question 4

How can we recover energy from waste

Answer 4

we burn waste to produce energy which is called incineration

Question 5

4 Advantages of waste recovery through incineration

Answer 5

 Electric and energy generated from waste reducing demand for electric
from power plants, saving fossil fuel use & associated effects.
 Developments in incinerator technology have reduced significantly the
emission of harmful gases from the incinerator plants.
 Reduced the volume of waste to landfill, and therefore the demand for
new landfill sites. Landfills are becoming increasingly difficult to locate,
particularly in densely populated areas.
 Reduces the emission of LFG including methane and CO2 which would
otherwise be pumped into the atmosphere through landfilling.

Question 6

3 disadvantages of waste recovery through incineration

Answer 6

 Still concern over the release of harmful gases into the atmosphere
through the incineration of waste.
 The ash residues must be disposed of which can be problematic as it
may in some cases be toxic.
 Local communities are generally opposed to the location of incinerator
installations in populated areas

Question 7

Explain low solid in terms of anaerobic digestion

Answer 7

low solid digestion is where the feedstock is around 15% solid material

Question 8

Explain residence time in terms of anaerobic digestion

Answer 8

The time taken for the full degration of the material in an aerobic digestion system

Question 9

Explain high solid in terms of anaerobic digestion

Answer 9

High solid digestion is where the feed stock is around 55% solid material

Question 10

Explain single stage in terms of anaerobic digestion

Answer 10

the biological reaction occurs in one holding tank and the biogas comes from this tank

Question 11

Explain multistage in terms of anaerobic digestion

Answer 11

Hydrolysis, acetogenesis and acidogenesis occurs in one tank whilst the methanogenesis which produces the biogas occurs in a separate tank.

Question 12

Name 8 different types of waste that can be treated by a compost heap

Answer 12

 Lawn clippings
 Shredded stalks
 Vegetable peelings
 Hedge clippings
 Cut flowers
 Teabags
 Leaves
 Egg shells

Question 13

Explain why composting is unsuitable for treating any form of catering waste

Answer 13

cooked food cannot be put into composting bin as it will attract vermin and other animals and insects

Question 14

Outline how anaerobic digestion can deliver both heat and power

Answer 14

Biogas from an AD plant can be burnt in a combined CHP plant, this generates
power (electricity) and heat.
Instead of losing the heat, as in traditional power plants, it is diverted into a local
heating system. This is co-generation.

Question 15

what is anaerobic digestion and what gases are produced

Answer 15

This is when bacteria break down organic material into sugars then into various organic acids which are further decomposed to produce biogas. This biogas, is a mixture of
methane, carbon dioxide, and trace gases, including hydrogen sulphide

Question 16

what are the 5 stages of anaerobic digestion

Answer 16

 mechanical pretreatment;
 hydrolysis;
 acidogenesis;
 acetogenesis; and
 methanogenesis

Question 17

how does anaerobic digestion result in biogas being produced

Answer 17

Hydrolysis takes place after mechanical pretreatment where insoluble polymers are broken down into organic soluble compounds. Then acidogenisis takes place where soluble organic compounds get fermented into volatile fatty acids. After this acetgoenisis takes place where alcohols and fatty acids are converted into acetic acid and
hydrogen. Finally methanogenisis happens where bacteria converts acetic acid and hydrogen into methane and carbon dioxide / biogas.