Waste management

Introduction
Waste worldwide
Anaerobic digestion: Psychrophilic digestion; Mesophilic digestion; Thermophilic digestion
Sterilization
Gasification/pyrolysis
Direct combustion

Waste

Waste, rubbish, trash, garbage, or junk is unwanted or undesired material.

There are a number of different types of waste. It can exist as a solid, liquid, or gas or as waste heat. When released in the latter two states the wastes can be referred to as emissions. It is usually strongly linked with pollution. Waste may also be intangible in the case of wasted time or wasted opportunities. The term waste implies things which have been used inefficiently or inappropriately.

Some components of waste can be recycled once recovered from the waste stream, e.g. plastic bottles, metals, glass or paper. The biodegradable component of wastes (e.g. paper & food waste) can be composted or anaerobicly digested to produce soil improvers and renewable fuels.

If it is not dealt with sustainably in this manner biodegradable waste can contribute to greenhouse gas emissions and by implication climate change.

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Waste management

Introduction

As municipal solid waste is being generated in increasing amounts all over the world, there is a greater need to reduce waste volumes heading for landfill. Thermal treatment technologies can do just this - more, they can offer an effective way of recovering valuable energy.

Many countries are at a crucial junction on the way to tackling the ever-increasing waste problem. A fresh look at their strategic options suggests that processes such as waste-to-energy (WTE) could play a more important role. This neglected energy source could also have a major impact on power generation at a local level. It would resolve some of the potential future electricity generation problems while conserving landfill space and helping to meet the requirements of the EU landfill directive and other landfill legislation worldwide.

Waste collection, transport and disposal into a landfill is not waste management. Managing waste is the collection and ultimate disposal of the waste without causing environmental damage. Every city in the world accumulates significant waste and has to deal with the problem of how to dispose of it. The amount of municipal waste generated per person can vary from 2 pounds per day per person up to 5 pounds per day per person, depending on the country and level of affluence. This amount does not include hazardous waste, industrial waste and other types of waste that are not included in the definition of municipal waste.

We believe that waste should be managed and treated as a resource not a liability. We believe that waste can be processed in an environmentally friendly manner that will eliminate the need for landfills in the future and that valuable products can be recovered from the waste. In order to accomplish this goal, we have marketed systems which convert virtually any type of waste into electricity, building materials and other valuable products.

Increase in waste arisings worldwide

While technological progress over the past three centuries has facilitated population growth through improvements in sanitation, medicine and intensive farming, it has also resulted in much more pollution. Material consumption has also grown to reflect both population growth and increased worldwide industrial globalization. With growth comes waste.

MSW arisings for EU-25 includes eastern European countries where the gross domestic product (GDP) is below that in the EU-15 Member States (i.e. excluding the 10 states that joined in 2004). This is reflected in the difference of only 26 million tonnes in the waste arisings between EU-25 and EU-15. In 2001, Japan generated just over 52 millions of MSW - a similar amount to that of Germany. However, the substantially different topographical conditions between the two countries mean that Japan needs to use extensive waste reduction measures to help resolve its disposal problems.

The variations in MSW production due to population differences are highlighted in the data shown for the US, UK, France, Germany, the Netherlands and Luxembourg. The values for waste generated per capita for these countries show significant variations. These are assumed to be a function of cultural and lifestyle differences, such as 412 kg/capita in Japan compared with 730 kg/capita in the US.

There is also a substantial variation in the amount of waste landfilled in the different countries. This is the result of the availability of disposal sites as a function of land mass, the use of other reduction technologies, recycling and local controls/ legislation.

Figures show the increase in the amount of MSW collected between 1995 and 2001. All show a substantial increase (from about 500 to 600 kg/capita) since 1995 - an average 3% year-onyear increase in waste arisings. The only difference is France where the growth is about half that of the other countries and the US where there has been a 1% reduction in MSW collected per person.

In general, if this growth is maintained up to 2020, the amount of waste generated/collected will double. This will cause even greater pressure on disposal routes. Landfill costs have also started to show dramatic increases; for example, costs in the UK have more than doubled since 2003.

Reuse, recovery and recycling strategies are unlikely to meet the potential growth in MSW. Other options thus need to be considered urgently. Thermal treatment processes offer viable alternatives.

The calorific value of MSW is about 10 GJ/tonne - about a third of that for coal. When burnt in a modern, well controlled mass-burn incinerator, such systems give about 20% efficiency for conversion to electricity. Much higher conversion efficiencies are possible with improved recycling and refining through processes such as mechanical-biological treatment (MBT) to create an energy-rich and consistent material that is better suited as a fuel. It is possible to achieve electrical conversion efficiencies of as high as 40%.