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Question 1

Briefly describe the waste minimisation hierarchy

Answer 1

The options for waste management are often arranged in this hierarchical manner to reflect their desirability. The aim of the hierarchy is to extract the maximum benefits from materials whilst generating the minimum amount of waste.
The first priority is waste prevention or reduction – that is, not producing the waste in the first place. If waste is produced then this should be minimised. The next priority is maximising reuse or recycling and recovery of suitable waste materials. Once the possibility of waste prevention have been exhausted then the next option is treatment, to reduce the volume of waste, to neutralise or render the waste harmless, to extract resources in the form of products and/or energy. The final option – and least desirable - is to dispose of the waste either to the air, water or land.

Question 2

A circular economy is one that exchanges the typical

Answer 2

A circular economy is one that exchanges the typical cycle of make, use, dispose in favour of as much reuse and recycling as possible. The longer materials and resources are in use, the more value is extracted from them. This could contribute toward reducing Europe dependence on critical materials such as cobalt, fluorspar or gallium, but also reduce overall demand by recovering the resources, nutrients or energy contained in products at the end
of their useful life.
Extending the life of products and materials
prevents the over generation of waste and recovers the full value of products. This would create new business opportunities and revenue streams, while minimising the environmental impact of mining, resource extraction, refining and manufacture.

Question 3

Ways to achieve waste avoidance/minimisation

Answer 3

1- Product design change:
Product design with less waste
Increase product life
2- Package change:
Reusable or recyclable pack, concentrate
3- Materials change:
Substitution of less toxic materials
4- Technological change:
Improved/more efficient equipment
5- Management practices:
Good housekeeping, inventory control

Question 4

Solid waste hazards

Answer 4

• Human pathogens
• Insects & rodents
• Animal pathogens
• Leaching
• Odour
• Soil pathogens

Question 5

Sources and types of solid waste

Answer 5

• Domestic:
  Food
  Paper
  Packaging
  Glass
  Metal
  Ashes
  Bulky household waste
  Hazardous household waste
• Commercial:
  Food
  Paper
  Packaging
  Glass
  Metal
  Ashes
  Bulky household waste
  Hazardous household waste
• Industrial:
  Industrial process wastes
  Metals
  Lumber
  Plastics
  Oils
  Hazardous wastes
• Construction and demolition:
  Soil
  Concrete
  Timber
  Steel
  Plastics
  Glass
  Vegetation

Question 6

5. Explain duty of care with respect to solid waste.

Answer 6

Industry and other businesses have a duty of care when it comes to waste. This means that the producer’s responsibility for waste does not end at the factory gate. This duty is placed on anyone who imports, produces, carries, keeps, treats or has control of waste (this excludes domestic waste).

Question 7

Waste management legislation

Answer 7

2008 EU Waste Framework Directive

2011 Waste (England and Wales) Regulations

2007 Environmental Permitting Regulations

2010 Industrial Emissions Directive (IED)

Question 8

Permit authorises treatment, keeping or disposal of controlled waste in
or on specified land

Answer 8

1996 Special Waste Regulation

2005 Hazardous Waste Regulations

Question 9

Waste minimisation hierarchy applied to solid
waste

Answer 9

• Reduction at source: Don’t produce it in the first place!
• Recycling/reuse: Recycling
• Treatment: Biological, Combustion, Gasification
  Pyrolysis (With/without Energy recovery)
• Disposal: landfill

Question 10

Chemical and energy properties

Answer 10

• Proximate analysis:
  Moisture content
  Volatile matter
  Fixed carbon
  Noncombustible fraction (ash)
• Ultimate analysis
  Carbon
  Hydrogen
  Oxygen
  Nitrogen
  Sulphur
  Ash
• Energy content MJ/kg

Question 11

Solid waste treatment options

Answer 11

1- Recycle
2- Biological
*Composting or aerobic
*Biogas or anaerobic
* Combined aerobic and anaerobic
3- Thermal
*Combustion
*Gasification
*Pyrolysis
* Energy from waste
4- Landfill

Question 12

Recycling example

Answer 12

Paper & cardboard
Glass
Aluminium cans
Plastics
Textiles
Batteries
Plus lots more!

Question 13

what is Biological treatment

Answer 13

Used to treat the organic fraction of waste
Reduces volume
Valuable products/energy
Waste becomes inert

3 options:
Aerobic composting

Anaerobic to generate biogas

Combined anaerobic and aerobic

Question 14

for Composting what are the process parameters

Answer 14

• Temperature
• Moisture content
• Oxygen
• C/N ratio
• pH
• Biochemical composition and texture

Question 15

Composting systems

Answer 15

Windrow
In vessel
Aerated static pile

Question 16

Issues with composting

Answer 16

• Heavy metals
• Odour
• Sterilisation
• Inert contaminants

Question 17

Anerobic digestion process parameters

Answer 17

• Oxygen free
• Stages
  *Hydrolysis
  *Acidogenisis
  *Methanogenesis

-Temperature control is important

• Biogas can be used as a fuel

Question 18

AD examples

Answer 18

GWE Biogas Ltd
*50,000 tonnes organic waste
*Local authorities, food manufacturers
and supermarkets
*Generate 2 MW electricity for export to
grid

Staples Vegetables
- Out of spec vegetables
- Electricity used on site or exported to grid
- Excess heat used to heat offices and buildings

Question 19

Thermal treatment types or options

Answer 19

• Incineration (combustion)
• Gasification
• Pyrolysis

( Waste to energy)

Question 20

Incineration process parameters

Answer 20

*Complete oxidation at high temperature

*Organic material is converted into heat, flue gas
and ash

IED sets stringent requirements:
*Minimum combustion temperature 850 C
for 2 seconds
*Specific emission limits for SO 2 , NO x , HCl,
CO, Total Organic Carbon (TOC)
*Ash to have organic carbon content < 3%

*Thermal efficiency up to 80- 90%

*Electricity generation ~ 27%

Question 21

Incineration technology

Answer 21

Moving grate (most common type)
Fixed grate
Fluidized bed
Rotary kiln

Question 22

Main factors that influence emissions from waste incinerators:

Answer 22

*Composition of the waste
*Combustion control
*Mechanical processes

Question 23

To control emissions:

Answer 23

*Combustion conditions for CO, VOCs and dioxins
*Ammonia injection for NO x
*Lime injection for SO 2 and HCl
*Carbon injection for capture of heavy metals
*Filter system for fly ash and other solids

Question 24

Gasification process parameters

Answer 24

*Thermal decomposition in the presence of a controlled amount of oxygen and/or steam
*Process occurs at high temperature (> 700 C)
*Produces syngas (carbon monoxide, hydrogen and some carbon dioxide)
*Gas can be used directly in engines to generate electricity

Question 25

Gasification equipment

Answer 25

• moving bed gasifier
• fluidized bed gasifier
• entrained flow gasifier

Question 26

what is Pyrolysis

Answer 26

Thermal conversion of waste in the absence of oxygen

Question 27

what are Pyrolysis types and products

Answer 27

Three types:
-Slow
-Intermediate
- Fast
Products:
*Pyrolysis liquid
*Char
*Gas

Question 28

Landfill random facts :)

Answer 28

*Last resort
*UK running out of landfill capacity
* Most landfill sites control and collect gas

Question 29

what is our biggest waste challenge?
What can we do? as As individuals, and As engineers?

Answer 29

plastics

As individuals
*Reduce consumption
*Reuse /recycle

As engineers
*New ways to re use plastics
*Develop biodegradable plastics
*Improve plastic recycling processes
*Reduce the amount of plastic used in processes

Question 30

A farmer is interested in developing an energy from waste plant to deal with the farm’s organic waste. What are the options? What would you recommend and why?

Answer 30

There is no single correct answer to this question. You should present the options available with a short description of each, with advantages and disadvantages. Then choose and justify a process for the farm’s organic waste