Recycling
( returning a waste to an intermediate stage of the
production process where it can be re-integrated
into making the same product gain)
Credits to Dr Philip Hall
Avoiding waste is a design issue; or rather of the philosophy, politics and economics
underlying the design specifications:
Asking for the solution that last the longest, is easily upgraded and repaired,
and can be dissembled into useable components after its long life (not the one that
makes the most profit for the shareholders of the producers)
NO WASTE
WASTE
Recycling is not at the top
of the waste hierarchy.
It’s only at the top of the part where avoiding waste has failed
Why?
Learning Outcomes
• Understand the principles of operation of the main unit operations used
for the recycling and separation of solid and particulate materials in
recycling and separation processes
• Develop a basic recycling/separation process flowsheet for a given
process stream, justifying the presence of each unit operation selected
• Apply material balances to calculate the efficiency of separation
processes
• Apply standard methods to select separation equipment based on
feedstock characteristics and product requirements, and estimate plant
costs
• Calculate the value or cost of any residues produced from recycling and
separation processes
Volume of household waste collected by local authorities per capita in England from 2010 to 2018 (in
kilograms)
Local authority collected household waste per capita in England 2010-2018
500
425 421 412 413 412
Kilograms per person per
402 406 403 394
400
300
year
200
100
0
2010 2011 2012 2013 2014 2015 2016 2017 2018
Note: United Kingdom (England); 2010 to 2017
Further information regarding this statistic can be found on page 35.
Source(s): Defra; Office for National Statistics (UK); ID 322535 Regular waste
Low or no population growth
Low or no increase in living standards
+ Incentives to avoid landfill
Amount of disposed garbage in China from
1990 to 2019 (in million tons)
How much waste would China produce if it each person produced
the same as
1 the UK 2 the USA ?
What can be recycled?
https://www.greenbiz.com/article/5-lessons-chinas-push-increase-domestic-recycling
The Chinese government….are
building basic trash sorting
systems and starting to charge
waste management fees for
both residential and
commercial waste for 46 major
cities by the end of 2020.
They’re also expanding their
trash classification system to
all cities by 2025.
2020 target: 35% recycling rates for residences
Materials Recovery Facility (MRF)
MRFs are processing plants that separate comingled materials
Two types: ‘Clean’ & ‘Dirty’
Difference: feedstock
Range of separation processes used based on:
• Feedstock properties
• Range and type of materials in feed
• Degree of mixing of materials in feed (co-mingling)
• Process plant throughput
• End-market specifications for products
‘clean’= low content on non-recyclable material; feeding the a clean MRF
is usually where the rules what can go into the recycle bin comes from
‘Clean’ MRF
Feedstock
– depends on collection system
– Paper and cardboard
– Glass jars and bottles
– Steel and aluminium cans
– Plastic bottles and film
– Textiles (less common)
Main advantage over ‘dirty’ MRF
– better quality materials
– Dry co-mingled recyclables separated at source
from organic material are cleaner
– Less contamination
All recyclables collected in one bin. Separate from organic waste
Watch: https://www.youtube.com/watch?v=wPrPcTqM67s (Bywaters)
https://www.youtube.com/watch?v=2eMk51ztMEE (Larnaca)
‘Dirty’ MRF
Feedstock
– Mixed waste
• Dry recyclables
• Organic materials
• Food Waste
• Bulky items (possibly)
• Special waste (possibly)
Main advantage over ‘clean’ MRF - no pre-sorting:
– Waste producers save labour and space by not having to
segregate their wastes at source
– Lower cost per unit as no collection costs are incurred by
recycling
BUT
– Increased health risk for employees of MRF
Everything in one bin. “ black bag”
Materials Recovery
Facility (MRF)
Still a high degree of manual pre- and post-sorting to protect the
machines and improve the purity of fractions
List of typical Unit-Op’s:
Unloading ; tipping floor or storage area
Metering
Conveying
Bag splitting
Screening for size
Screening for shape (surface area)
Size reduction
Air classification (density)
Cyclone (density/size)
Magnetic separation
Eddy current separation
Specialised Fibre separators
Sensor based / optical separation
Unloading and conveying of waste
• Dirty MRF
– Raw MSW is unloaded onto concrete tipping
floor
– Refuse is spread by a front-end loader
– Large bulky items or special waste are
removed
• Clean MRF
– Mixed recyclables are unloaded at the materials
reception area
– Transfer to a sorting line via a series of feed
conveyors
Further feed preparation operations
Bag splitting
• Relatively gentle shredder
• Splits plastic bags whilst leaving
majority of waste intact
• May be damaged by large hard objects
Flow metering
• Uneven flow of materials on conveyors
reduces efficiency of downstream
processes
• Manual slow feed e.g.from tipping floor
to initial conveyor
Size reduction
(also known as breakage or comminution)
Materials entering process
not optimum size for
processing
• Easier to change
particle size to fit
equipment
Make materials easier to
separate
• Control flow into
different unit
operations
• Liberate different
materials (if you break
it small enough)
Comminution– energy/size relationship
Some size reduction unit operations
Mechanical separation
• Negative sorting
The removal of unwanted materials to leave
remainder for automatic sorting further down
process
• Positive sorting
The removal of specific recyclables by staff or
machinery, the remaining product is the residual
material
More commonly used
Screening
Screening uses a geometrical pattern for size control
• Performance of screens controlled by 3 parameters:
Motion – Inclination – Screening media
Screening - motion
Screening example: Trommel Screen
• rotating cylinder with holes of various sizes through which materials fall
• Inclined down towards discharge end; finer material falls out first
• No wear parts so low operating/maintenance costs
• Up to 60 t/hr throughput
