How to Generate Energy From Waste
Waste is plentiful. Landfill sites and sewage dumps around the world are growing faster than you can say overpopulation. They pollute our land and our waters. (find out about the global water crisis here…)
It is expected that this year(2011), there will be 7 billion people on this planet. It’s becoming a very crowded place in the blue marble, and it is starting to show. Overpopulation and our increasing thirst for oil have turned vast amounts of the world’s surface into toxic landfill waste sites. Pollution levels are at record highs and it seems we are all destined to leave our houses with radiation suits at some point in our future history unless we change the way we deal with our waste matter or we reduce the amount of waste we produce (virtually impossible unless we all move to another planet).
There is a possible solution…
Why not turn all that waste into something useful, like fuel for our homes?
Harnessing the energy in waste can reduce carbon emissions and relieve the pressure on landfill sites and sewage treatment plants.
It can be done. Basically, any organic matter can be used to produce energy.
Energy can be generated from all kinds of organic matter (including waste) through one of the processes described below:
Anaerobic digestion (AD) or Methane Recovery
Around 90 million tonnes of waste is produced in the UK each year, of which 62% is biodegradable†. AD replicates the natural process that occurs in
landfill sites. Organic waste can be reduced into matter that can be used for high quality fertilizer similar to compost. During this process methane can be siphoned off and used as fuel. Alternatively, although less efficient, the methane produced in landfill sites can be used directly as fuel.
After taking into account efficiencies and the energy content of the gas methane, AD could potentially supply the UK with 1.9% of the current energy demand…or it can continue to sit and rot in landfill sites across the globe…
Burn it baby. Although mass waste incineration has been used for decades, tighter regulations on pollution have meant that capacity has fallen. New cleaner technologies mean that relatively safe direct incineration of municipal waste is now viable in urban areas. Using the same calculation method as above (with AD) direct incineration of waste could provide 5% of the UK’s energy demand, not much when you say it out loud, but consider that it will be also reducing waste to landfill by nearly 60%.
Gasification / Pyrolysis
Pyrolysis and Gasification (P&G) are very similar technologies. They involve the processing of waste in an oxygen-free (pyrolysis) or oxygen-reduced environment (gasification). Pyrolysis produces rich oil and solid residue known as ‘char’, which can be burnt as fuel. Gasification only produces gas from the waste.
The main advantage of P&G over direct incineration is that the process retains any pollutants. Efficiencies are also higher (approximately 35%) making it feasible to provide up to 9% of the UK’s energy demand. P&G can also work at smaller scales where direct incineration is neither viable nor economic (less than 150,000 tonnes of waste a year).
Of course there are drawbacks. The main one being the need to prepare the waste: fuel needs to be shredded or broken down before entering the gasifier, and this involves extra cost. This I believe is the main reason why it is not a commercially viable option. Public opinion still opposes large-scale incinerators for reasons of visual intrusion and possible harmful emissions, so the absence of any emissions should be seen as an important benefit, plus you still need to burn fuel to make the whole thing work!
Energy from Waste key points:†
1. Energy can be obtained from waste through anaerobic digestion, direct incineration, pyrolysis or gasification
2. Reduces the amount of waste sent to landfill, but may conflict with recycling objectives.
3. Modern technologies are cleaner and more efficient
4. Can be used at both large and small scales
5. Cost will depend on the technology used. However, as it is possible to offset some of the costs of waste disposal against energy from waste it can cost as little as £0.05 (GBP) per kWh generated†