Our aim is to minimise the amount of leftover waste by preventing or reducing waste in the first place, re-using wherever possible, and recycling. But there will always be a proportion of waste which needs to be dealt with in other ways. Many new technologies are emerging to do this. Here are details of some of them.

Anaerobic Digestion
Anaerobic digestion is a series of processes in which micro-organisms break down biodegradable material – in a similar way to composting – in the absence of oxygen.  It takes place in a warm sealed airless container. Anaerobic digestion is a renewable energy source as it produces biogas which can be used to generate heat and electricity, a fibre which can be used as a soil nutrient, and a liquid fertiliser. Small anaerobic digestion plants can be designed to treat the biodegradable household waste of a village or group of villages, or a farm’s agricultural waste. At the larger end of the scale, centralised facilities can be developed to deal with household waste, agricultural waste, sewage sludge and industrial organic wastes.

Materials Reclamation Facility
A materials recycling facility or materials recovery facility is a specialised plant which receives, separates and prepares recyclable materials. When the materials have been carefully separated by members of the public and left for collection at the kerbside, this is known as a clean MRF. When recyclable items are brought in un-sorted, this is called a dirty MRF.

Mechanical Biological Treatment
A mechanical biological treatment system combines a sorting facility with a form of biological treatment, such as composting or anaerobic digestion. It is designed to process mixed household waste as well as commercial and industrial wastes. The mechanical sorting removes cans and glass, as these materials are of value and not suitable for use as fuel. Material remaining is biologically treated in one of several ways to yield useful, less smelly products. They will produce less methane if sent to landfill, and in some cases could be used as fuels.

Mechanical Heat Treatment
This is similar to mechanical biological treatment and is sometimes called autoclaving. The waste is treated in large vessels using heat and/or steam, sometimes under high pressure conditions. The treated waste is then removed for mechanical or manual separation. The process makes the waste dry and odourless, and it can be further processed as a fuel, or sent to landfill.

Energy Recovery
Waste is burned at temperatures high enough to destroy any airborne chemicals that could potentially be harmful to health. The heat released from this process is recovered and used to generate electricity, which is fed into the national grid. Modern energy recovery facilities include highly sophisticated equipment to reduce pollution before anything is emitted into the atmosphere. The technology is now effective enough to be 20 times cleaner than chimneys in private households. Such facilities reduce the volume of the original waste by 95-96%, which greatly reduces the amount of waste going to landfill. Even the ash from these facilities can be put to good use in the construction and road building industries. Some of Europe’s best recycling nations achieve their figures by using this type of facility. Denmark for instance have long been leaders in the race to recycle and send 53% of their waste to energy recovery facilities.

Pyrolysis
Waste is mechanically sorted and separated in a variety of ways. Anything left after this process is dried out and biologically treated, often using anaerobic digestion processes. The waste can then be further processed for fuel and because the moisture content is lower and cans and glass are not present, more energy is recovered than when using untreated waste. If it is sent to landfill, it also gives out less methane than untreated waste.

Gasification
Gasification is a method of extracting energy from many different types of organic materials. It involves a chemical reaction which takes place at very high temperatures. During the process carbon is converted to syngas, leaving a solid residue. This takes place in the presence of air or air enriched with oxygen. Energy can then be generated from gasification to produce steam or electricity.

In-vessel Composting
In-vessel composting is one option for the disposal of animal by-products from food processing and manufacturing plants, distribution premises, wholesale and retail outlets, food markets and catering facilities. The process is strictly controlled and normally occurs in large sealed metal tanks or concrete bunkers. Air flow and temperature inside these containers are measured to ensure the waste is properly treated to a point where it can safely be spread on land and used as a soil improver. In-vessel composting is a proven treatment process, and a wide choice of technologies exists. There are around 600 installations worldwide.