Maximizing Organic Waste: Anaerobic Digestion for Methane Reduction, Food, and Energy Security

According to the Global Methane Pledge, the waste sector is responsible for nearly 20% of global anthropogenic methane emissions (Global Methane Pledge, 2022). While it is the fourth leading source of methane emissions, methane overall is responsible for approximately 30% of the rise in global temperatures (Ellerbeck, 2022). The issue with methane is that it has a global warming impact of about 86 times that of carbon dioxide on a 20-year timescale (RMI, 2024). In 2020 alone, the global methane emissions from municipal solid waste landfills had an equivalent global warming impact of 4.4 billion metric tons of CO2 on a 20-year timescale (RMI, 2024). That is about 950 million passenger vehicles.  However, most methane in the waste sector comes from organic waste, consisting of food and green waste.

Sufficient technologies and techniques exist to reduce methane emissions from organic waste and convert food waste into biogas for energy use. Like natural gas, methane from organic waste can be used to power our cities. The process of anaerobic digestion is an exceptional innovation that separates food waste into fertilizer for agriculture and biogas for electricity generation, ensuring energy and food security. In essence, it is a process of decomposition by bacteria that separates waste into valuable gases and residues.

Why is organic waste management important? What is anaerobic digestion and how does it provide food and energy security? And what is done to mitigate methane emissions in the waste sector?

These are some of the questions the blog explores.

Inspired by a recent experience with ImplementaSur, a Chilean climate consultancy, this blog post dives into the importance of organic waste management and anaerobic digestion as a tool for climate action that amplifies our food and energy security.

Image source: https://news.uga.edu/organic-waste-management-can-reduce-greenhouse-gasses/

According to the World Bank, “the world generates 2.01 billion tonnes of municipal solid waste annually, with at least 33 percent of that—extremely conservatively—not managed in an environmentally safe manner. Worldwide, waste generated per person per day averages 0.74 kilogram but ranges widely, from 0.11 to 4.54 kilograms. Though they only account for 16 percent of the world’s population, high-income countries generate about 34 percent, or 683 million tonnes, of the world’s waste” (Kaza et al, 2018). Respectively, of the total global solid waste generated, approximately 44% is food and green waste (Figure 1).

Figure 1: Global waste composition (percent). Image source: Kaza et al, 2018

Unlike one may guess, high-income countries' proportion of food and green waste is only 32% of total waste, while in middle- and low-income countries the ratio rises to respectively 53% and 57% (Kaza et al, 2018). Organic waste output decreases in the long run relative to economic development, substituted for an increase in other waste types (Kaza et al, 2018). Except for Europe, North America, and Central Asia, organic waste in all other regions comprises on average about 50% of the total waste composition (Kaza et al, 2018). Global total waste production is expected to grow significantly in the next few decades, particularly in East Asia and Pacific, South Asia, and Sub-Saharan Africa (Figure 2).

Figure 2: Projected waste generation, by region (millions of tonnes/year). Image source: Kaza et al, 2018

Aside from detrimental methane emissions, organic waste has direct environmental risks, pressures our public healthcare systems through disease spread, impacts food supply chains and impacts animal biodiversity exacerbating ecosystem loss (Sun and Yu, 2023; Conti et al, 2024; Kiyasudeen et al, 2016; Newsome and Eeden, 2017). Thus, as organic waste produces a serious present and future cost to our economy, a keen new solution is anaerobic digestion which can turn this cost into the benefit of improved food and energy security.

So what exactly is anaerobic digestion? Well, according to the US Environmental Protection Agency (2024), anaerobic digestion is a process where bacteria decompose organic materials—such as animal manure, wastewater biosolids, and food waste—in an oxygen-free environment. The process occurs in an enclosed environment or sealed container. Within, complex microbial communities break down the waste, producing two valuable outputs: biogas and digestate.

Biogas primarily consists of methane (CH4), similar to natural gas, and also contains carbon dioxide (CO2), hydrogen sulfide (H2S), water vapor, and trace amounts of other gases. The energy from biogas can be harnessed for heating, electricity generation, and cooling. By removing unwanted components like CO2 and H2S, biogas can be upgraded to renewable natural gas (RNG). This RNG can be fed into the natural gas grid, compressed for vehicle fuel use, or refined into other energy products or advanced bio-based materials. Unlike natural gas extracted from fossil fuels, biogas production from organic waste is considered a net-zero solution, since it uses a biofuel grown within our lifetime.

Digestate is the leftover material after the digestion process, comprising both solid and liquid components. These are often separated and processed separately due to their differing applications. The solid fraction can be used for animal bedding, as a nutrient-rich fertilizer, as a base for bio-based products like bioplastics, or as compost. The liquid fraction can be used as a fertilizer or soil amendment. These digestate products can provide additional revenue or cost savings, enhancing the financial and environmental outcomes of the project, serving the local green economy, and reinforcing food security. 

The above diagram illustrates the Anaerobic Digestion process in detail. Diagram source: Environmental Protection Agency, 2024

With the forecasted growth of total global waste generation, large-scale anaerobic digestion plants are a valuable source of ecologically sustainable energy production that can complement the growing renewable energy industry and the energy transition (Tryhuba et al, 2023). Particularly in the context of rising geopolitical supply chain risks in the Middle East, Eastern Europe, and the South China Sea. Moreover, anaerobic digestion produces nutrient-dense fertilizer that can substitute synthetic chemicals to promote crop health, and enhance soil resilience and climate adaptation, increasing food security by reducing risks of crop failure (Severn Trent, 2023). Therefore, governments should be swift to include innovative organic waste management policies as part of their climate-driven agendas.

Notably, however, the regulation set out to reduce methane emissions in the waste sector is a more recent conception, enacted after the Paris 2015 Convention. But it wasn't until almost six years later in 2021 that it was followed by the largest movement towards methane mitigation measures as the establishment of the Global Methane Pledge (GMP) at COP26 in Glasgow. Since March 2024, the GMP counted 158 participants (Global Methane Pledge, 2024). These participants take voluntary actions to reduce mitigation emissions through a pledge in six action areas including the Energy Pathway, the Waste Pathway, the Food and Agriculture Pathway, Methane Plans and Policies, Data for Methane Action, and Finance for Methane Abatement (Global Methane Pledge, 2024). The movement accounts for roughly 50% of global emissions, lacking larger emitters such as Russia, China, India, Venezuela, and Turkmenistan (IEA, 2024).

There are additional organizations that support (or were established to support) the GMP such as the Climate and Clean Air Coalition (CCAC), the UN Environment Programme (UNEP), and the Global Methane Hub (GMH). These provide opportunities to facilitate voluntary methane reduction actions by assisting with public and private project financing, providing technical assistance or evaluating potential projects, assisting with feasibility studies, providing additional investment and grant opportunities, and much more. Action for methane mitigation in the waste sector is steadily growing.

Conclusion

In conclusion, effective organic waste management, particularly in the form of anaerobic digestion, offers a critical pathway for reducing methane emissions, enhancing food security, and bolstering energy security. As global waste generation continues to rise, anaerobic digestion technology adoption presents a dual opportunity: mitigating the significant environmental threats posed by methane while transforming organic waste into valuable resources like biogas and nutrient-rich digestate. It not only helps in addressing climate change but also supports local economies, the energy transition, and agricultural resilience. With the looming climate crisis and the commitments under the Global Methane Pledge, governments should be held responsible for accelerating the implementation of organic waste management policies as part of their climate change agendas. By harnessing the potential of anaerobic digestion, we can turn the challenge of organic waste into a powerful tool for sustainable development, ensuring a more secure and resilient future for all.

References:

Conti, G. O., Pulvirenti, E., Cristaldi, A., & Ferrante, M. (2024, March 15). Organic Waste Management and Health. ScienceDirect. https://www.sciencedirect.com/science/article/pii/B9780443135859000136?via%3Dihub

Ellerbeck, S. (2022). This is how cities can reduce emissions with waste-reduction solutions. World Economic Forum. https://www.weforum.org/agenda/2022/11/waste-emissions-methane-cities/

Environmental Protection Agency. (2024, January). How Does Anaerobic Digestion Work?. EPA. https://www.epa.gov/agstar/how-does-anaerobic-digestion-work

Global Methane Pledge. (2022). Waste pathway. Homepage. https://www.globalmethanepledge.org/annual-report/waste-pathway

Homepage: Global methane pledge. Homepage | Global Methane Pledge. (2024). https://www.globalmethanepledge.org/#about

Kaza, S., Yao, L. C., Bhada-Tata, P., & Van Woerden, F. (2018, September 20). What a waste 2.0. Trends in Solid Waste Management. https://datatopics.worldbank.org/what-a-waste/trends_in_solid_waste_management.html#:~:text=The%20world%20generates%202.01%20billion,from%200.11%20to%204.54%20kilograms

Key findings – global methane tracker 2024 – analysis. IEA. (2024). https://www.iea.org/reports/global-methane-tracker-2024/key-findings

Kiyasudeen, Katheem & Ibrahim, M. & Quaik, Shlrene & Ismail, Sultan Ahmed. (2016). Organic Waste Management Practices and Their Impact on Human Health. 10.1007/978-3-319-24708-3_11.

Managing methane in the waste sector. RMI. (2024, May 16). https://rmi.org/our-work/climate-aligned-industries/managing-methane-in-the-waste-sector/

Newsome, T. M., & Van Eeden, L. M. (2017, July 19). The effects of food waste on wildlife and humans. MDPI. https://www.mdpi.com/2071-1050/9/7/1269

Sun, F.-S., & Yu, G.-H. (2023). Fate of bio-contaminants in organic wastes during composting and vermicomposting processes. Fate of Biological Contaminants During Recycling of Organic Wastes, 143–156. https://doi.org/10.1016/b978-0-323-95998-8.00004-2

The benefits of using digestate instead of fertiliser: a sustainable solution for agriculture. Severn Trent. (2023, November 16). https://www.stgreenpower.co.uk/insight/the-benefits-of-using-digestate-instead-of-fertiliser-a-sustainable-solution-for-agriculture

Tryhuba, I., Hutsol, T., Tryhuba, A., Cieszewska, A., Kovalenko, N., Mudryk, K., Glowacki, S., Bryś, A., Tulej, W., & Sojak, M. (2023). An approach to assessing the state of organic waste generation in community households based on associative learning. Sustainability, 15(22), 15922. https://doi.org/10.3390/su152215922