Introduction to Waste and Waste Managment Flashcards
What is the definition of waste?
‘Any substance or object which the producer or the holder discards or intends or is required to discard with the exception of: radioactive waste, prospecting, extraction and treatment of minerals, animal carcasses and agricultural waste, wastewaters, gaseous effluents’
How much MSW do we produce globally each year?
2.12 billion tons
How much of what we buy is thrown away within 6 months?
99%
What is waste generation driven by?
Economic developments and urbanisation
Which two countries produce the most waste?
USA and Canada
What are the five types of waste disposal?
Open dumping, landfill, recycle, incineration, open burning
What type of disposal does North America utilise the most and why?
Sanitary landfill because they have so much uninhabited land
What does MSW mean?
Municipal solid waste
What does OECD mean?
Organisation for Economic Co-operation and Development
Where is 50% of the waste in the UK generated?
Construction
How much available MSW does the UK produce each year?
30 million tonnes
What potential does the waste the UK produces annually have in both electric power and heat power?
2,000 MW electricity, 6,000 MW heat energy
How much of the UK’s power does MSW have the potential to replace and what is this in MTCE (million tonnes of coal equivalent)?
The same as a large power station - around 5%, 10 MTCE/year.
How much of the energy that could be provided by MSW is currently recovered?
Around 5%
What does the Waste Strategy 200 hope to achieve?
Reduce waste sent to landfills (by 65% by 2015 from 1995), recover 67% of waste by 2015 and recycle or compost 33% of household waste
What are the four types of waste?
Municipal solid waste, industrial waste, sewage sludges and special waste (eg. clinical waste)
Define MSW
MSW includes non-hazardous waste generated in households, commercial and business establishments, institutions, and non-hazardous industrial process wastes, agricultural wastes and sewage sludge
What is the typical composition of MSW
paper and card, plastics, textiles, glass, ferrous metals
What is the typical calorific value of MSW?
7-11 MJ/kg
What is the typical moisture content of MSW?
30-35%
What is the typical calorific value of industrial waste and what does it depend on?
Up to 30 MJ/kg
Why do feed rates of industrial waste have to be limited?
To avoid excessive temperatures
What is the average calorific and moisture content of sewage sludge?
3-4 MJ/kg and over 90% water
How must sewage sludge be pre-treated before incineration?
It must be dried to a moisture level below 65% before incineration can be self-sustaining
Name 3 devices used for de-watering sludge
Vacuum filters, belt filter presses, centrifuges
What are sludges moved through processes using?
Belt conveyors, screw conveyors, plunger pumps or progressive-cavity pumps
Why is no extensive storage required for sludge incineration?
It is usually generated close to the incinerator location
Define special waste
Waste containing hazardous materials such as flammables, explosives, toxic, radioactive, pathogenic or clinical waste
What is a typical calorific value of special waste and say why this is the case?
Hospital waste approx. 17 MJ/kg due to a higher plastic content than MSW.
Why does special waste require special incinerator design?
Due to it’s toxic nature
What is the waste hierarchy, what is its aim and what is it based upon?
It is an evaluation of processes that protect the environment alongside resources and energy consumption, its aim is to extract the maximum practical benefits and to generate minimum waste and is based on sustainability (a socio-ecological process characterised by the pursuit of a common ideal).
In what year did the EU parliament introduce the waste hierarchy into its waste legislation?
2008
What are the 6 steps of the waste hierarchy?
Prevention, minimisation, reuse, recycling, energy recovery, (safe) disposal
Give examples for implementing the ‘prevention’ step of the waste hierarchy.
Use less material in design and manufacture, keeping products for longer, using less hazardous material
Give examples for implementing the ‘preparing for re-use’ step of the waste hierarchy.
Checking, cleaning, repairing, refurbishing whole items of spare parts
Give examples for implementing the recycling step of the waste hierarchy.
Turning waste into a new substance or product - includes composting if it meets quality protocols
Give examples for implementing the ‘other recovery’ step of the waste hierarchy.
Anaerobic digestion, incineration with energy recovery, gasification and pyrolysis which produce energy (fuels, heat and power) and materials from waste, some backfilling operation
Give examples for implementing the ‘disposal’ step of the waste hierarchy.
Landfill and incineration without energy recovery
What is considered to be the ‘greenest’ way of dealing with waste, and why are they not often used?
Biological treatment (often generate heat), not used as they are very slow
What does the decision between biological treatment and thermo-chemical treatment depend on?
What waste there is available in the surrounding area and the local demand for the products
What is the advantage and disadvantage of thermo-chemical treatments?
They produce more valuable products but require an energy input.
Name the 3 types of thermo-chemical treatment
Gasification, incineration and pyrolysis
Name the 2 types of biological treatment
Composting and anaerobic digestion
What is the product of composting?
Compost
What is the product of anaerobic digestion?
Methane
What are the products of gasification?
Fuel, gas and ash
What are the products of incineration?
Energy, flue gas and ash
What are the products of pyrolysis?
Char, oil and gas
Where does the ash from both biological and thermo-chemical treatments end up?
In landfill
What are the two avenues to segregate waste?
Segregation an source and segregation at materials recovery facility
Name two waste pre-processing technologies
Size reduction and separation
Give an example of a local MRF
SITA Kirklees
What are the two products from waste pre-treatment?
RDF (refuse-derived fuel) and SRF (solid recovered fuel)
What does MRF stand for?
Materials recovery facility
Give two options for disposal of waste
Landfill and open dumping
What are the three types of thermo-chemical treatment of waste?
Incineration, pyrolysis and gasification
What are the two types of biological treatment of waste?
Composting and anaerobic digestion
Describe the different types of waste segregation at source.
House containers or kerbside collection (inc. dry recyclables which can be sorted or co-mingled), drop-off centres, buy-back centres and refund deposit schemes.
What are the two types of MRF?
Dirty MRF and clean MRF
What separation occurs at a dirty MRF?
Mixed MSW is dumped and recyclable bits picked, of in a high tech facility it is separated and recovered
What separation occurs at a clean MRF?
Screening and separating different grades of papers, metal separation, glass sorting and processing and shredding plastics.
Name two waste size reduction equipments
Hammer-mill (grind raw materials in smaller particles, 5-100 tons/hr depending on the input), industrial waste shredder
Name and describe two waste separation technologies
Magnetic separation (strong permanent magnets based on rare earths catch metal within a stream of bulk materials) and Air Classificiation (separates materials based on a combination of size, shape and density using air and a cyclone)
Draw a magnetic separator
Drawing 2
Draw an air classifier
Drawing 3
What is tommel screening?
A rotating perforated drum is elevated at one and and particles of different sizes pass through the holes as the waste travels down the drum.
List the stages in a typical solid waste sorting process
Bag ripping, magnetic separation, shredding, air classifying, tommel screening
What are the advantages of pre-treating and sorting waste?
Increased material recovery for recycling, removal of non-combustible materials and better control of final disposal and energy recovery (increasing the heating value, increasing plant throughput, lower carbon-in-ash), less waste to landfill, and producation of refuse-derives fuel (RDF)
What is the capacity of the Kirklees MRF?
25,000 ton/year
How much paper and plastic is recovered at Kirklees?
19,500 ton/year
How much ferrous cans are recovered at Kirklees?
750 ton/year
How much non-ferrous cans are recovered at Kirklees?
750 ton/year
What are the typical heating calues of MSW and RDF?
MSW 10 MJ/kg and RDF 15-20 MJ/kg
What is cRDF and how is it produced?
Coarse refuse-derived fuel, separating from MSW its bulky and non-combustible fractions (glass, rubble etc.) and chopping the rest to a consistent size. It cannot be stored as it starts rotting immediately.
What is dRDF and how is it produced?
Densified refuse-derived fuel, the separation of bulky and non-combustible fractions, followed by substantial reduction in moisture content and then pelletized.
Is cRDF or dRDf better for thermal processing?
dRDF due to it’s higher energy content, however it is more expensive to produce
What is SRF and how is it different from RDF?
Solid recovered fuel that is produces to EU standards, it has large proportions (up to 68%) of organic material found in MSW and is used for the production of power and heat. It contains a smaller amount of ash and has a CV of 11-14 MJ/kg
What are the differences between sanitary landfill and open dump?
Sanitary landfill is legal, controlled by the government, is carefully monitored so pests are avoided and are less hazardous to the environment than open dumping. They have leachate collection systems and are often smaller.
What is leachate?
The liquid that drains from a landfill site. It varies widely in composition depending on the age of the landfill and the type of waste, and usually contains both dissolved and suspended solids.
Draw a typical landfill site
Drawing 4
What are the two main advantages of controlled land fill?
It is low cost compared to other disposal options and is suitable for a wide variety of wastes.
What is the main disadvantage of landfill sites?
They are sources of pollution since uncontrolled gas leakages containing methane can be hazardous.
What is the key difference between the three thermo-chemical treatments?
The amount of oxygen supplied to the reactor
What three characteristics of waste are important for its assessment?
Moisture content (ignition will not occur if it is too wet, and it diminishes the CV), volatile matter (the combustible fraction containing carbon monoxide, hydrogen and methane), ash content (high ash = lower CV and must be removed and disposed of after combustion)
Define incineration
The oxidation of the combustible material in the waste to produce heat, water vapour, nitrogen and carbon dioxide
Which amount of oxygen matches to which thermo-chemical treatment?
Excess O2 - combustion
Limited O2 - gasification
No O2 - pyrolysis
Draw and describe a typical waste incineration plant
Drawing 5
What smaller emissions may you obtain from waste incineration depending on the type of waste?
Carbon monoxide, hydrogen chloride, hydrogen fluroide, sulphur dioxide
Which country incinerates the most amount of MSW?
France
Which country incinerates the most amount of industrial waste?
Finland
Where do the residues from flue gas treatment in an incineration plant go?
Hazardous landfill
Where does heavy bottom ash from incineration go to?
Landfill
Where do metal extracted from the heavy bottom ash go from an incineration plant?
Recycling
What are the advantages of incineration over landfill?
Reduces MSW by 90% in volume and 67% by weight as only ash remains, provides low cost energy, bottom ash can be used as a construction material, reduces greenhouse gas emissions
What are the disadvantages of incineration over landfill?
High capital costs, ash requires additional management, public perception
Define pyrolysis
The thermal degradation of organic waste (such as plastics and polymers) in the absence of oxygen to produce a carbonaceous char, oil and combustible gases.
What temperature is pyrolysis usually carried out at?
Low temperatures - between 400 and 800 degrees C
How is heat supplied for pyrolysis?
Indirect heating (combustion gases or oil) or directly by hot gas transfer
What is conventional/slow pyrolysis?
Pyrolysis with moderate heating rates (20-100 degrees C/min) and a max T of 600 degrees C to give an approximately equal distribution of oils, char and gases.
What is very slow pyrolysis?
Less than 20 degrees C/min heating rate and a low final maximum temperature maximises the yield of char
What is very fast pyrolysis?
High heating rates (100-1000 degrees C/min) at T below 650 degrees C with rapid quenching leads to the formation of mainly liquid products (oils)
How do the relatively high CVs of pyrolysis chars produced from MSW, tyre and wood compare to the CV of bituminous coal?
MSW - 19 MJ/kg
Tyre - 29 MJ/kg
Wood - 33 MJ/kg
Coal - 30 MJ/kg
How do the high CVs of pyrolysis oils produced from MSW, and tyres compare to the CV of petroleum-derived fuel?
MSW - 25 MJ/kg
Tyre - 42 MJ/kg
Petrol - 46 MJ/kg
Where can oil from pyrolysis be used?
Conventional electricity generation systems such as diesel engines
What are the advantages of the production of oil through pyrolysis?
It can be transported away from the plant easily
What are the main gases produced from MSW pyrolysis?
CO2, CO, H2, CH4
What does the composition of oil produced pyrolysis depend on?
The feedstock and processing conditions
What two main routes are being researched to overcome high oxygen content, high viscosity and acidity of oils produced by pyrolysis?
High pressure catalytic hydro-treatment and low pressure catalysis
Which oils tend to have a high oxygen content?
Those derived from some biomass sources (up to 35% oxygen by weight) due to the content of cellulose, hemicellulose and lignin
Define waste gasification
Oxygen in the form of air, steam or pure oxygen is reacted at a high temperature with available carbon in the waste to produce a gas product (syngas), ash and tar
What operating temperatures are typical for air and oxygen gasification?
Air - 800-1100 degrees C
Oxygen - 1000-1400 degrees C
How do the CVs of air gasification and oxygen gasification compare to natural gas?
Air - 4-6 MJ/kg
Oxygen - 10-15 MJ/kg
Natural gas - 37 MJ/kg
What is the premise of the reaction that occurs in gasification?
Partial combustion occurs to produce heat, and the reaction proceeds exothermically to produce a low to medium calorific value fuel gas
How are gasification products utilised?
Direct combustion in a boiler or furnace to provide heat or power generation.
What is the advantage of direct combustion of gasification products?
No syngas cleaning is required
For what utilisation of gasification products should they be cleaned to a higher specification than for direct combustion?
For use in gas turbines or internal combustion engines to generate electricity
List the gasification and steam gasification chemical equations
Drawing 6
Which thermo-chemical treatment of waste is most mature?
Incineration, therefore benefits from large scale
Give 2 examples of early stage commercial gasification plants
Compact Power (UK) uses pyrolysis + gasification (air/steam) then combustion, cost £22m (capex) for 60 kton/year and £76/ton (opex) Thermoselect (Japan) uses pyrolysis + gasification (oxygen) then combustion then ash melting, cost £69m (capex) for 200 kton/year and £345/kton (opex)
What are the electricity efficiencies for incineration and gasification?
Incineration - 20-25%
Gasification 30-45%
What efficiency is achieved in CHP and why?
Around 85% as it utilises low grade heat
Which fraction of waste can be used in composting?
The biodegradable fraction, therefore reducing the amount that goes to landfill
Define biodegradable waste
Food and garden waste
What proportion of MSW is biodegradable?
66-90%
How long does composting take?
Relatively fast biodegradation process taking 4-6 weeks to reach a stable product
Does composting use oxygen?
Yes, it is aerobic
What are the 3 stages of composting?
1 - Increasing temperature because of a high rate of micro-biological activity
2 - stabilisation - biodegradation of the waste by thermophilic micro-organisms and is exothermic (up to 70 degrees C)
3 - maturation - further dergradation of intermediate compounds and may take several weeks - low temperature
Why is composting better than landfill?
Less greenhouse gases (carbon dioxide and methane) are produced
What is the product of composting?
Organic matter that has been decomposed and is recycled as a natural fertiliser and soil amendment
What is the best option for true green waste?
Composting
What kind of reactor does anaerobic digestion take place in?
An enclosed, controlled reactor without oxygen.
What is the product of anaerobic digestion?
Gas rich in methane to use as either fuel or chemical feedstock.
What is AD used to treat?
Sewage sludge and agricultural wastes, and more recently MSW and industrial wastes
How is AD optimised to ensure all the gas is collected?
Through process control
Describe the AD process.
Easily degradable organic matter > soluble monomers > organic acids > methane/CO2
Difficult to degrade organic matter > residual organic matter
What can the solid residue from AD be used for?
As fertiliser
How long does AD take?
40 days/6 weeks
What is water used for in AD?
To so dissolve the monomers so they can turn into organic acids.
Draw a BFD for a typical AD plant
Drawing 7
What does pre-treatment involve in AD?
Chopping, sorting, mixing and the removal of contaminants
What does the main stage of AD involve?
Heating and mixing to produce methane and carbon dioxide.
In what environment does biodegradation take place?
In a slurry of waste and micro-organisms.
What does the rate of biodegradation depend on?
The micro-organism population and the temperature (from 30-65 degrees C)
What does AD post-treatment involve?
The removal of further contaminants (glass and plastics) and further stabilisation through composting of the residue.
