We haven’t discovered the secret to time travel, but we can generate electricity and heat from waste or convert it to a synthetic fuel.There are a number of ways we can do this, but some of them carry significant risks.
Energy from waste can be organic or inorganic.
Organic energy is produced when organic waste is converted into a fuel, usually methane. The process helps us safeguard our environment because it recovers a valuable resource (methane) and reduces pollution in the atmosphere.
Inorganic energy is produced when high-calorific materials, such as plastics, are recovered from existing materials. The plastics used to generate inorganic energy are most often those that can’t be recycled. By the time they are available to generate energy, their exact composition and origin is often unknown.
There are three principal ways in which we can convert waste to energy using thermal energy: combustion, gasification and pyrolysis.
Combustion involves incinerating organic waste, and substances like plastics and textiles. The incineration process turns the waste into heat, which in turn can be used to generate electricity.
Gasification converts materials containing carbon, such as coal, petroleum, and organic waste, and plastic, into carbon monoxide and hydrogen. It does this by converting the raw material at high temperatures with a controlled amount of oxygen. The resulting synthetic gas (syngas) is itself a fuel. Gasification is a very efficient method for extracting energy from many different types of organic materials.
The third process – pyrolysis – uses heat in the absence of oxygen to decompose organic waste. It can convert complex materials such as organic and product waste into synthetic gas.
Biochemical conversion uses microbes to convert organic waste into energy sources such as methane-rich biogas and ethanol. There are a variety of technologies based on this biological treatment, including anaerobic digestion and fermentation.
Anaerobic digestion uses microorganisms to break down biodegradable material in the absence of oxygen. This creates a gas that is rich in carbon dioxide and methane and not only reduces the mass of organic waste, but also leaves a nutrient-rich residue that can be used as fertilser.
Fermentation converts organic waste into an acid or alcohol in the absence of oxygen. This releases energy from the organic material, leaving a nutrient-rich residue.
Thermal energy conversion, such as incineration, is the focus of most environmental concerns around turning waste to energy. Thermal technologies emit microscopic particles of matter and liquid suspended in a gas (particulates) and pollute our air.
These particulates can be toxic and increase the risk of heart and lung disease, diabetes, damage to thyroid and death in humans. In animals, they increase the risk of cancer, hormone disruption and birth defects.
In addition, incineration facilities produce a large amount of fly-ash (a residue of incineration) that contains accumulated toxic materials such as dioxins and heavy metals that must be disposed of in hazardous waste facilities.
Pyrolysis and thermal gasification carry many of the same risks.
But we do not support the development of inorganic waste-to-energy facilities until there is: