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*Updated November 2022
With an approximate 1% annual growth of the global population in the past few years, there’s no getting around the pressing concern of finite resources and a tired Earth. Sadly, the population isn’t the only thing that’s growing - with increased urbanization, landfills and various greenhouse emissions (primarily methane) are also growing at an alarming rate all over the world.
One way to divert trash from landfills and convert it into something truly useful is to turn waste into energy. This is made possible through waste-to-energy technologies of varying eco footprints and efficiency. Although largely underutilized around the world, the sector is very promising, especially now, at a time when global energy insecurity has reached a new and, quite frankly, distressing peak. So let’s take a look at the most innovative waste-to-energy technologies that could help us localize energy production and decrease the negative impact of landfills.
How does waste-to-energy technology fit into the bigger picture?
Governments can no longer evade the fact that sustainable development is the very least we should strive for in today’s climate - and we say climate both in terms of weather and economy. A promising solution, one that’s been recently adopted by the European Commission's plan of action for a greener future, is the concept of a circular economy.
A circular economy seeks to lengthen the lifespan and use-value of products to reduce pollution and waste. It’s everything you’ve heard about sharing, giving, borrowing, lending, recycling, reusing, composting, and all that other good stuff. One of its principal building blocks - or rather, its principal point of contact with broader environmental efforts - is waste-to-energy.
What is waste-to-energy?
Simply put, waste-to-energy is any process that converts waste (or trash) into a source of usable energy, which is why it’s categorized as a type of energy recovery. Waste-to-energy solutions can turn gaseous, liquid, and semi-solid waste into heat, fuel for transport, or electricity. The trash that gets used by waste-to-energy technology is non-recyclable, meaning there’s no other way to convert it into something useful. Waste-to-energy companies manage waste by turning it into energy.
In urbanized areas, the most common source of trash for waste-to-energy companies comes from municipal waste, i.e. the trash that we all accumulate on a daily basis and can’t be recycled or composted. The process is referred to as municipal waste treatment, or MWT.
According to a 2018 study, several EU countries, including Sweden, Denmark, Finland, Germany, and the Netherlands have managed to keep landfills to an incredible 1%, instead of redirecting the majority of municipal waste either to recycling and composting or to waste-to-energy technologies via MWT.
While traditionally, the most commonly used method for waste-to-energy (WtE) conversion has been incineration, there are lots of up-and-coming, progressive waste-to-energy that show greater promise with fewer caveats, such as concerns about the toxic gasses that come from trash incinerators.
Keep in mind that for waste-to-energy technologies to be truly a part of a circular economy, it’s important that all compostable and recyclable waste is composted and recycled. As we’ll cover towards the end of this article, some of the main criticisms of WtE plants arise from the concern that repurposable trash won’t be repurposed so it can end up as energy.
Types of waste-to-energy solutions
Waste-to-energy technologies are divided into different types based on the process through which the waste is turned into energy: thermal only, which includes incineration, thermo-chemical, mechanical & thermal, and biochemical.
Thermal WtE plants are most common in handling MWT. This includes any sort of waste management that uses heat to turn trash into treasure, i.e. power. However, the first thermal WtE method, incineration, is one of the least favorable options because incineration plants are costly to operate and have higher rates of emissions. Instead, let’s focus on what we came here to do - look at the most innovative technologies in waste-to-energy.
Anaerobic digestion (AD)
Anaerobic digestion is a biochemical process that takes feedstock and places it in a reactor in the absence of oxygen to create biogas and digestate. The waste is broken down inside of reactors that are rich in microbial communities.
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The biogas resulting from AD is mainly made up of methane (the very same methane that arises from landfills, though here it’s used for a purpose) and carbon dioxide. It also contains trace amounts of water vapor, other gasses, and contaminants.
Anaerobic digestion biogas can be used as a transport fuel, heat, and electricity. The other product of the AD process, the digestate, is a solid or liquid substance that can be used as a fertilizer and to create bio products like construction materials or animal bedding.
Anaerobic digestion, however, is not as efficient as some other waste-to-energy technologies we’ll talk about below. In fact, its estimated energy efficiency is 40%, at best. There is also room for concerns regarding emissions.
Finally, a significant financial drawback of AD plant management comes from the high maintenance cost for the proper handling of biogas and ensuring that no leaks or harmful waste seep into the air and soil.
Future waste-to-energy technology in this sector would need to divide its focus between improving efficiency, decreasing emissions, and building an infrastructure that would reduce the chance of leakage and cut maintenance costs.
Gasification
Gasification is a thermal WtE method that’s generally considered a much better alternative to incineration, as its product (syngas) gets cleaned before (rather than after) use. In other words, gasification waste-to-energy plants produce much less pollution than traditional incinerators.
Gasification uses municipal waste as a feedstock rather than a fuel and converts it into syngas under high temperatures. Syngas is a combustible synthetic gas (where the name comes from, clearly) that can be used as fuel for transportation, an alternative to natural gas, and for fertilization. Keep in mind that most gasification plants require careful sorting and pre-processing of municipal waste, as not all materials are suitable for gasification.
What’s great with gasification is that it works with non-recyclable plastics without emitting harmful air pollutants. The newest development in gasification comes in the form of plasma gasification, or plasma arc gasification.
Plasma gasification
Plasma gasification utilizes a plasma torch at extremely high temperatures (generally between 5,000°C and 7,000°C, but can be higher or lower) in a single reactor to turn feedstock (biomass, coal, municipal waste, etc.) into that very same syngas (mainly made up of hydrogen and carbon monoxide) we just talked about. This breakdown of molecules and change of chemical composition due to plasma torching is also referred to as plasma pyrolysis.
Not only is the resulting syngas used as fuel and cleaned prior to use, but plasma gasification also creates valuable byproducts. The glass-like byproduct of the process, i.e. the slag that remains from the melted waste of plasma falsification, is safe to use as a construction material. If you’re worried about toxins, don’t! Plasma torches have been utilized to destroy toxic waste and chemical weapons in the past.
The downside here is that dioxins still get released as the syngas cools down. Still, they’re significantly less in comparison to the dioxins (and furans) that are formed at traditional incinerator plants. Needless to say, future-proof waste-to-management technologies are geared towards this direction, as it’s both efficient and pollutes less.
Hydrothermal carbonization (HTC)
Hydrothermal Carbonization (HTC) is a thermochemical process that turns organic waste into structured carbons similar to fossil fuels (that take up to millions of years to form naturally). HTC works with wet feedstock, and the process combines an acid catalyst and pressure at somewhat high temperatures (180 to 250°C) to produce hydro-char, this fossil fuel-like product that has high levels of carbon.
Not only can hydro-char be used as fuel but it can also be used to replace coal. The obvious benefit of this is avoiding the many drawbacks of coal mining. The product can also be used to enrich soil, and the feedstock can be used for gasification.
The main advantage of HTC over other thermochemical technologies like pyrolysis is that it doesn’t require pre-treatment (pre-drying) of the feedstock, as it’s designed to work with wet waste, which makes the process a lot faster.
It also requires similar operating conditions to anaerobic digestion for the same energy output. This, combined with the faster processing time, gives HTC an edge over competitive WtE methods like anaerobic digestion.
However, the ecological effect of this novel technology remains largely unknown. A recent study that compared using HTC to using mono-incineration plants for sewage sludge in Germany found that HTC is more sustainable, but that the use of hydrochar in agriculture instead of NPK-fertilizers had high emissions. So, there are a lot of parameters that we need to monitor when searching for the cleanest ways to turn waste into energy.
The future of progressive waste solutions: dendro liquid energy (DLE)
Dendro liquid energy (DLE) is probably the most promising up-and-coming, near-zero emissions waste-to-energy technology that treats waste biologically. DLE plants operate at moderate temperatures between 150°C and 250°C, which makes them about four times more efficient in generating electricity when compared to anaerobic digestion and other WtE solutions.
Dendro liquid energy plants work with both wet and dry waste to generate clean fuels for electricity like hydrogen and carbon monoxide - basically, it produces syngas. What’s more, DLE is cost-efficient because the process doesn’t contain combustion, meaning it doesn’t need expensive anti-emission technology to be environmentally safe.
Some of the main advantages of DLE are that it has a high energy conversion of around 80% efficiency, and near-zero emissions, meaning the byproduct and syngas don’t contain particulates and tar. Its low operating cost makes it a perfect local solution for various municipalities. Waste-to-energy engineering will hopefully allow increased access to DLE in the near future, as, for one, it’s a very fertile market, and, for another, the ongoing energy crisis has revealed that a degree of independence is crucial if we - any country on earth, really - is to withstand difficult times. We need more independence in both food and energy production, and waste-to-energy technologies like DLE provide opportunity for the latter.
The drawbacks of waste-to-energy technologies
The potential of waste-to-energy technology is undeniable, though there are some caveats we can’t ignore if we want to paint a complete picture. Some major criticisms are directed at WtE efforts by the global zero-waste movement.
These mainly revolve around the harmful byproducts of WtE facilities (incinerators release pollutants in the air), the fact that waste is a non-renewable energy source, the questionable efficacy of WtE plants, and the fear that waste-to-energy technologies would reduce the focus on repurposing and recycling waste products.
Financial burdens
Some real-life examples show that these concerns are not unfounded. For instance, Copenhagen’s Amager Bakke waste-to-energy plant has already taken a financial toll on taxpayer’s money - both because of technical problems and the fact that the plant’s capacity for waste is too high.
What’s more, over half of the cost of operating a WtE plant goes to reducing harmful emissions. Of course, this problem is sidestepped by the most promising developments in waste-to-energy technology, like DLE.
Pushing recycling to the background
In Australia’s New South Wales, the main concern has to do with what the local WtE plant would mean for recycling. As we already mentioned, for waste-to-energy to be reasonably energy-efficient and a financially sound investment, WtE plants need a constant and consistent stream of waste.
Skeptics argue that before we resort to burning our trash to create energy, we need to do our best to repurpose it first. Precisely due to this concern, the Confederation of European Waste-to-Energy Plants (CEWEP) emphasizes that only waste that can’t be otherwise recovered would be used within their plants.
The final verdict - for now
This is all normatively right - zero-waste is the most sustainable way forward. However, the reality is that recycling, let alone zero-waste efforts and efficient use of renewable energy, are far from widespread and efficient enough. On the other hand, in most environmentally-conscious countries that employ waste-to-energy technologies, only non-recyclable trash is delivered to the WtE plants.
Additionally, studies show that even the incineration of biowaste (with anti-emission technology of course) as a part of the process maintains a negative global warming potential and is therefore deemed eco-friendly. This is incomparable to the amount of methane and smog that landfills release, damaging the environment and our health.
Yet, reports from 2022 show that global “superpowers” are still lagging behind in our bid to turn waste to energy. For instance, the US “mismanages” or landfills about 80% of plastic waste, and, worse yet, it landfills over 90% of its post-recycling waste. This means that a very low percentage of waste gets turned into energy. Europe is doing better on all counts, but China has taken a leading role in this movement by replacing landfills with WtE solutions in the past 15 years. Its WtE capacity exceeds that of the US, EU, and Japan combined. Additionally, the mass production of such plants in China has made waste-to-energy technology more readily available to developing countries in Asia and Africa. This helps fulfill the need we underlined earlier: greater independence in food and energy production.
So, despite some of the drawbacks of waste-to-energy technologies, they appear to be a crucial step in dealing with the negative effects of growing landfills - as long as only non-recyclable, non-repurposable materials are fed into WtE machines and the necessary measures are taken to minimize air pollutants. They also may prove to be an important bit of help in securing energy on a local scale in the upcoming era of uncertainty.
On a brighter and greener note, the growing need for better WtE technologies has led to developments like DLE, processes that have near-zero emissions, are cost-efficient and energy-efficient.
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