Picture yourself after a party or family gathering. As you clean up the decorations and dishes, a lot of waste should be disposed of, which we usually do without thinking twice. We just sort it into different containers and move on. Nonetheless, this waste does not simply disappear; it has to be processed, and in some cases, it will persist for many years. It might not come as a surprise that our waste is linked to climate change, however, it might be in a way different from what you imagine. Let’s explore the challenges we face regarding waste management and what we can do to overcome them.
What happens to the waste we produce?
Waste generation and management differs greatly from place to place due to many socioeconomic and geographical factors. The general trend shows that waste generation is closely linked to economic development; the higher a country's income, the higher the amount of waste generated. To put this into perspective, high-income countries, or 16% of the world’s population, produce about 35% (~ 683 million tonnes) of the world's waste. On the other hand, low-income countries, which comprise 9% of the population, produce about 5% of the global waste (~ 93 million tonnes).
Waste varies not only in amount but also in composition. High-income countries produce more packaging materials like paper and plastic, while lower-income countries have more organic waste such as food and agricultural residues. Understanding waste composition is crucial for efficient management. Recyclable materials like glass, metal, plastic, paper, and electronics are valuable if uncontaminated. Otherwise, incineration is more practical. Organic waste is suited for composting or energy generation, while construction and industrial waste, mainly inorganic, offers no energetic value. Effective waste management depends on these distinctions to maximize resource recovery and minimize environmental impact.
If we take a look at the different strategies to manage waste, we find that landfilling is one of the most utilized. From the estimated 2.01 billion tonnes generated in 2016 around the world, about 37% ended up in landfills, 33% in open dumps, 19% were processed through recycling and composting for recovering materials, and 11 % was treated with modern incineration methods (World Bank, 2018).
In Denmark, we are privileged to have an excellent system for collecting, separating, recycling and even converting waste into products like compost or energy. Waste collection in Copenhagen is estimated at 100% coverage (World Bank, 2018). Organic waste from households and agriculture is used to produce biogas, and we have one of the most advanced waste-to-energy plants, Copenhill. But, what happens to the waste that cannot be recycled or recovered? - You guessed right, it still goes to the landfill.
Landfills
Landfills are considered a convenient and economical waste management strategy in contrast with other facilities, such as modern incineration plants, which pose greater technical and economic challenges. During operation, sanitary landfills can act as a sink for pollution that otherwise would get into the environment. After a landfill has reached its capacity, it is closed and monitored to evaluate potential leaks of leachates into the groundwater or emissions to the atmosphere. It is usually assumed that, if well handled, landfill sites don’t pose any risk to the environment or human health after 30 years, given that most of the waste is assumed to be degraded (Cossu & Stegmann, 2019).
Different microorganisms break down organic waste in landfills. If there is no oxygen (anaerobic conditions), methanogens produce CH4 and CO2 from the waste. If oxygen is present (aerobic conditions), the waste mainly degrades into CO2, water, and stable humic substances. You may wonder what happens to the inorganic waste that microorganisms can’t break down. Well …In most cases, it will stay in the landfill, though rain can wash some substances into leachates, which are hopefully treated at a wastewater treatment plant.
The landfill is full, now what?
When a landfill reaches its full capacity for storing waste, the landfill cell is closed and the “aftercare” period begins. In theory, when the site reaches compliance with environmental regulations, it can be repurposed, and the aftercare period ends. Unfortunately, it has been observed that in some old landfills reaching the end of the aftercare period, emissions (e.g., leachate and greenhouse gases) do not meet environmental regulations yet. As a result, operators must extend the aftercare period. This is a problem since they must absorb the costs of monitoring and providing maintenance to the site, originally budgeted for 30 years.
A way to tackle this issue is to implement longer aftercare periods during the design of the landfill. However, as you can imagine, predicting when the waste will fully degrade and ensuring the site is safe is challenging, especially since many landfills lack detailed records of their contents. Better control of the incoming waste to the landfill is highly beneficial, and we have improved significantly in this regard since modern landfills emerged in the latter half of the last century. More stringent legislation has also reduced the amount of waste being landfilled and narrowed down the type of waste allowed at landfills. For example, the European Union has introduced a directive to reduce municipal landfilled waste to 10% by 2035, prohibiting biodegradable municipal waste, recyclables, and materials suitable for energy recovery from landfilling. Nevertheless, as previously mentioned, the implementation of waste management and its legislation varies greatly depending on the region.
Another approach is to accelerate waste degradation. Organic content in landfills degrades slowly under anaerobic conditions, often causing landfill gas emissions for decades and leachate issues that can persist for centuries. Since aerobic degradation is much faster, landfill aeration has been developed to speed up waste stabilization. This method introduces atmospheric air into the waste, changing conditions for the microorganisms. On top of reducing the production of methane gas, landfill aeration also reduces organic content in leachates, and helps to manage odours.
So, if there are already some solutions, why are emissions from landfills still an issue?
The impact of landfill emissions
As we mentioned, two of the main products of waste degradation are CO2 and CH4. Both are greenhouse gases, which means that they are quite good at retaining heat. This is usually an advantageous characteristic; without greenhouse gases in our atmosphere, the average temperature would be -18°C instead of 15°C (NASA, 2010). However, the concentration of these greenhouse gases has significantly increased since the Industrial Revolution, leading to excessive warming, and the now infamous climate change.
In terms of its global warming potential (GWP), methane is around 28 times more effective at trapping heat than carbon dioxide (IPCC, 2022). This means that even if there are lower emissions of CH4 in comparison with CO2, their influence on climate change is much more severe. On the bright side, CH4 has a shorter lifespan than CO2. So, if we manage to promptly reduce CH4 emissions we can also make a significant impact on climate mitigation in the short term.
Coming back to the landfills, if we consider that in most cases waste degradation is carried out by anaerobic bacteria producing CH4, we can understand why landfills account for about 18% of the man-made methane emissions in the EU (EEA, 2022).
What can we do to reduce landfill emissions?
The generation of CO2 and CH4 is unavoidable in landfills since they are the main products of waste degradation. However, we can reduce their impact on climate change by tackling methane generation. We can implement technical and legal strategies to this end. For example, in landfills where the production of methane is high, it can be recovered and used as fuel. On the other hand, in landfills with low organic content, aeration could be a potential solution to further reduce CH4 and accelerate waste degradation. As for the legal aspect, reducing the amount of waste, specifically organic waste in landfills as suggested by the EU directive has proven useful. For example in Denmark, landfilling combustible waste was banned in 1997 (decided in 1994 and coming into effect on 1 January 1997) (Kjær, 2013). The effects of the legislation can be seen in the reduction in the contribution to the emissions from the waste sector. In 1990, 87% of the CH4 emissions from the waste sector in Denmark came from solid waste disposal - aka landfilling - whereas by 2018, it was reduced to 49% (Nielsen et al, 2020). Furthermore, restrictions that reduce waste generation, and promote recycling and incineration, in 2021, only about 3.3% of the waste generated in Denmark went to landfills (Miljø Ministeriet, 2024).
References
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Cossu, R., & Stegmann, R. (2019). Solid Waste Landfilling—Concepts, processes and technologies. Elsevier. https://doi.org/10.1016/C2012-0-02435-0
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