Beyond Recycling
Central Government has set tough targets for the UK to drastically reduce the amount of the waste that is sent to landfill from 22.3 million tonnes in 2000 to 12.2 million tonnes in 2020 (with a target of 15.9 million tonnes by 2010). This is a reduction of 45%. These targets are supported by escalating taxation on all waste that is sent to landfill. The standard rate of tax will increase by £8 per tonne year on year.
In order for local authorities to support Central Government achieve these targets, not only do they need to work with communities to raise recycling levels and reduce waste, they also have to find alternative ways of dealing with rubbish that cannot be recycled or composted.
Project 65% explains what new technology Peterborough City Council is looking to use in the next few years and how this and other schemes are planned to get them to a recycling rate of over 65% for household waste by 2020.
Find out more about the future of waste in Cambridgeshire in the next few years to see how 'residual waste' (waste that cannot be recycled or composted) will be dealt with.
Methods for dealing with 'residual waste'
Incineration and Energy from Waste
What is incineration?
Incineration is the controlled burning of rubbish
at high temperatures, which may or may not be
carried out with energy recovery. Incineration
can be an attractive option for dealing with rubbish
because once the rubbish has been burnt it can
be only 10% of its original volume, reducing the
amount that has to be buried in the ground.
Incineration - How?
Rubbish taken for incineration arrives at a sorting
station and has large unsuitable items removed.
The rubbish is lifted and deposited onto a moving
grate, which transports the rubbish into the combustion
chamber to be burnt.
What's Left?
Any materials that cannot be burned and the bottom ash remains. These are removed from
the grate into a water tank for cooling. These materials can then be buried in landfill.
The process also produces a very fine ash called Fly Ash. Fly Ash contains pollutants that are removed in the chimneys of the incinerator.
How do we deal with the Pollutants?
Modern incinerators have measures in place to
control the emissions they release to the atmosphere.
These have to comply with tough standards set
by European and UK legislation.
The measures are designed to
control Acid emissions (using scrubbers), dust
levels (using electrostatic precipitators) and
fine particles (using fabric filters).
Fly ash is caught by these processes
and has to be disposed of carefully in special
landfill sites that are licensed to accept toxic
rubbish.
Energy Recovery - How does this work?
Heat generated by the incineration process is
used to generate hot water and steam. The steam
is used to drive a turbine which produces electricity. At the end
of this process the waste hot water can be piped
and used directly to heat homes and other buildings.
This is known as combined heat and power (CHP).
These technologies are already well established
worldwide and in the UK.
Whilst extracting some value
from non-recyclable rubbish can been seen as a
preferable option to landfill disposal, 'Waste
to Energy' (WTE) processes like this are governed
by strict planning and licensing laws. These are
to protect and eliminate possible impacts on the
health of humans, animals and our environment.
Cambridgeshire and Peterborough residents are not in favour of incineration and
intend to pursue this only as a last resort.
Landfill
What is Landfill?
Landfill is rubbish buried in
holes in the ground (or piled on the ground in which case it is called landraising) and left to rot. The exception
to this is rubbish deposited on the surface of
the ground or landraising.
Landfill is the most common
form of disposal for our household rubbish in
both Cambridgeshire, Peterborough and nationally
with about 80% going to landfill.
There are two main reasons
that Councils must find ways of dealing with our
rubbish other than landfilling it.
- We are running out of space both locally and
nationally
- The number of good sites are decreasing so
we must be careful with the sites we have and reduce what goes in to them
How does Landfill work?
Many landfills were first quarries or extraction sites. Landfills are slowly filled
with layer upon layer of rubbish, which is compacted
daily with heavy machinery. This squashing of
the rubbish removes air and creates more space
in the site. Since the landfill is essentially
starved of oxygen the rubbish breakdowns under
"anaerobic conditions". However, any
air left quickly goes to help rot organic rubbish,
such as food, garden and paper waste. Once the
landfill is full it must be capped and can be
turned into public spaces, such as golf courses.
What is left and what are the problems?
Landfills produce a "biogas",
most of which is methane. The amount of methane
released into the atmosphere by landfill sites
has become a growing concern , because methane
production is one of the biggest contributors
to global warming and changes to our climate.
Landfills also create a liquid called leachate
that is produced by the rotting process. Leachate
is controlled to prevent it polluting underground
water systems. Lastly, many of the manmade "disposable"
products, such as nappies and plastic bags, can
take several hundred years to rot away.
How is the pollution dealt with?
Most landfills are designed
with the necessary controls to reduce impacts
on the environment and human health. For example,
landfill sites have to be specially lined to prevent
any leakage of toxic leachate. In addition, a
process called "Flaring" has been developed
to manage methane gas. The gas is channelled through
pipes on the landfill site and is burnt or flared
at the surface. Burning the methane changes it
to carbon dioxide and water, which is less damaging
to the climate. It is also possible on some landfill
sites in the UK to capture the Methane and use
it as a fuel to generate electricity.
To stop waste going to landfill it is important to reduce and reuse our rubbish.
Mechanical Biological Treatment (MBT)
MBT is a generic term used to
describe a range of processes. There are three
typical stages to MBT:
- Biological drying - rubbish is shredded
in a fully enclosed plant, and then dried
using either enclosed windrows or in-vessel
composting for 12-15 days. Microorganisms
digest the organic material killing germs
and smells and evaporating water. The drier,
more stabilised material has a weight reduction
of 25%
- Material separation – equipment is
used to separate ferrous and non-ferrous materials,
for example aluminium and steel, for recycling;
glass, stone and grit are removed as low-grade
aggregate
- Resource use – recyclates are sent
to reprocessors; all biomaterial can be sent
to landfill and should meet landfill directive
requirements for treatment. Smaller biomaterial
can be used as landfill cover; depending on
quality, some material can be used in land
reclamation; coarse, combustible material,
known as ‘flock’ or pellets, can
be used as RDF (Refuse Derived Fuel) in incineration
or pyrolysis/gasification plants
Mechanical Biological Treatment (MBT)
| Advantages |
Disadvantages |
| Process contributes to diverting
organic waste from landfill |
At present, a large proportion
of the waste that goes through the process
has to be landfilled or combusted (other uses
are quality dependent) |
| Potential recovery of recyclables, particularly metals |
|
| Produces a product which could
be used for engineering, land reclamation
or as a fuel |
There is currently no real market
for end-product |
Anaerobic Digestion
This is a well established and
widely used method for treatment of various types
of waste and rubbish. It is traditionally used by the
agricultural and farming industry to process slurries
(animal waste) and by water companies to treat
sewage sludge. This is an ideal technology for
dealing with the organic part of household rubbish,
for example paper, food and any garden rubbish,
and as an alternative to landfill. It is a carefully
controlled process to prevent the inclusion of
heavy metals, for example batteries.
What is it and how does it work?
The term "Anaerobic Digestion"
means bacteria breaking down, or digesting, organic
material without the presence of oxygen.
The organic portion is extracted
from rubbish, is shredded, and fed into a "digester"
where it is heated and will start to breakdown.
Normal household rubbish is not as wet as the
sludges traditionally used in this process,
so water or some of the sludge can be added
to help the process.
What is produced and what about pollution control?
This process produces useful
products such as biogas, which is made up of Carbon
Dioxide and Methane.
As with Gasification,
this biogas can be burned and used to generate
electricity or/and heat for the surrounding area.
This gas is continually drawn off and captured
under controlled conditions to prevent any leakage
of pollutants. Another product of this process
is called "digestate", which is a solid material. This can be used as a soil conditioner
like compost. Lastly, a liquid is produced which
can be used as a liquid fertiliser.
Comparisons
This process is similar to the breakdown of organic rubbish in a landfill site which also produces methane but:
- All of the biogas and liquid from this system
is captured and utilised
- The liquid produced is not harmful in the
same way as leachate from landfill sites
- The breakdown of the organic rubbish happens
in a fraction of the time that it would in landfill
- There is control over the type of rubbish
used at any one time, which reduces the risk
of contamination
- The process would still require some of its solid product to be landfilled
Anaerobic Digestion is being used in many countries to treat household rubbish,
but there are no major plants as yet in the UK. This
treatment could also be used in conjunction with
others systems such as recycling schemes.
Pyrolysis and Gasification
What is this?
These are two different technologies
that are quite similar in their process and the
product produced. Both of them involve the use
of heat to change your rubbish into a useful product,
however, does not heat your rubbish to burning
or combustion point.
Gasification
Rubbish is likely to be sorted
first to remove inorganic materials that will
not breakdown easily with heat, such as glass
and metals. The material left is then heated with
a little oxygen to the point where it is turned
into gas. The gas produced can be used as a fuel
to generate electricity.
What is left?
There are a number of materials produced by this process including tars, inert
chars and ash. But this can vary depending on
the Plant and the type of rubbish being treated.
Pyrolysis
This is the heating of your
organic rubbish but without the presence of Oxygen.
This also produces a gas, which can be used as
fuel.
What is left?
This process produces char
and pyrolysis oil.
Pollution concerns
These technologies are attractive because compared with incineration
the emissions to the atmosphere are low and it
produces a saleable fuel. Also the volume of residues
to be buried in landfill will be considerably
less than the volume of the original rubbish.
Other concerns
As with many rubbish treatment
plants, planning controls have to be taken into
account and a suitable site has to be found. To
make such plants economical it's beneficial to
have the treatment plants near the power generating
plants in urban areas.
These technologies are still in their early stages but are already being used in the
UK to treat other kinds of waste not domestic
rubbish. Cambridgeshire and Peterborough Authorities
will be keeping themselves up to date of the latest
developments and how this technology might play
a part in our rubbish management.
