Central Government has set targets for the UK to drastically reduce the amount of the waste that is sent to landfill from around 75% in 2002 to less than 20% by 2020.
In order to do this we will have to find alternative ways of dealing with rubbish in addition to recycling.

Examples of some of the existing technologies to help do this are explained below.
Cambridgeshire is entering into 25 Year PFI (Private Finance Initiative) contract to provide new waste management facilities to help meet our targets.
For more information click here.

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 ash, called Bottom Ash, is remaining. This is removed from the grate into a water tank for cooling. The material can then be buried in landfill.

The process also produces a very fine ash called Fly Ash. Fly Ash contains pollutants that is removed in the chimneys.

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, used to light buildings and homes. 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 result.

Landfill

What is Landfill?

Landfill is rubbish buried in holes in the ground 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 a quarry or an extraction site. 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?

Landfill's 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 Lechate 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:

  1. 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%.
  2. 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.
  3. 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. 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 sludge's 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.

  • 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 than 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 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 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 early stages but are 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.