With an approximate 1% annual growth in population globally 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.
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 looks 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 generally 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 epitomizes what a circular economy is.
In urbanized areas, the most common source of trash for these types of progressive waste solutions comes from municipal waste, i.e. the trash that we all accumulate on a daily basis and can’t be recycled or composted. This 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 solutions that show greater promise with fewer caveats, such as concerns about the toxic gases 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 for more trash to be converted to energy, less of it would be appropriately repurposed.
Types of waste-to-energy solutions
In general terms, 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 digest. To do that, reactors are rich in microbial communities that serve to break down the feedstock.
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The biogas resulting from AD is mainly made up of methane (the very same methane that arises from landfills, but here it’s utilized for “good”) and carbon dioxide, though it also contains trace amounts of water vapor, other gases, and contaminants.
Anaerobic digestion biogas is a type of natural gas that can be used as a transport fuel, heat, and electricity. The other product of the biogas, 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 at 40%, at best, and there is room for concerns regarding emissions. Plus, due to maintenance needs, like the proper handling of the biogas and ensuring that no leaks or harmful waste seep into the air and soil, AD plant management is somewhat costly.
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 utilizes a plasma torch at extremely high temperatures (generally between 5,000 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 by-products. 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.
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 product can also be used to enrich soil, while 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.
The future of progressive waste solutions: dendro liquid energy (DLE)
Dendro liquid energy (DLE) is probably the most promising and 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. Furthermore, it works with mixed waste (dry and wet) to produce clean fuel and its low operating cost makes it a perfect local solution for various municipalities.
The drawbacks of waste-to-energy technologies
The potential of waste-to-energy is undeniable, though there are some caveats we can’t ignore if we want to give a complete picture. Some major criticisms directed at WtE efforts that are pointed out by the global zero-waste movement, mainly revolve around the harmful byproducts of WtE facilities (incinerators release harmful pollutants in the air).
And 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.
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 objectively true - 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 developed in most of the world. 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.
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.
On an even brighter 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.
Innovation here is what is driving the sustainable technologies of waste-to-energy forward. One way to stay ahead of the curve when it comes to disruptive technologies is to incorporate data-driven insights into an industry or sub-sector.
This is harder than it looks and it's something that us at Valuer want to make easier. With our platform you can keep on top of innovation and disruptive technologies through our AI-based platform that lifts the veil of unknowns and let you discover any possibility or solution you can think of. Innovation is key to a sustainable future, let us help you get there.