Manure Digesters on Farms Carry Limited Benefits and Potential Harms – Johns Hopkins Bloomberg School of Public Health

Report on the Efficacy of Manure Digesters in Achieving Sustainable Development Goals

Introduction: Assessing Agricultural Technology Against Global Sustainability Targets

A recent study from the Johns Hopkins Bloomberg School of Public Health evaluates the role of manure digesters in sustainable agriculture. While promoted as a technology to advance Sustainable Development Goal 13 (Climate Action) and SDG 7 (Affordable and Clean Energy), the research indicates that their benefits are overstated and may conflict with other critical SDGs, including SDG 3 (Good Health and Well-being) and SDG 6 (Clean Water and Sanitation). The paper, published in Current Environmental Health Reports, deconstructs claims made by proponents and concludes that the technology’s potential hazards may outweigh its limited environmental advantages.

Analysis of Climate Action and Energy Contributions (SDG 13 & SDG 7)

The primary justification for the promotion and subsidization of manure digesters is their capacity to reduce greenhouse gas emissions and generate renewable energy. However, the study’s findings challenge their effectiveness in contributing to these goals.

• Limited Impact on SDG 13 (Climate Action): The report highlights that methane from untreated manure constitutes only about 11% of total U.S. agricultural greenhouse gas emissions. Manure digesters can only address a fraction of this percentage, resulting in a minimal overall impact on climate targets. This limited benefit can be further diminished by biogas leaks and an increase in nitrous oxide, another potent greenhouse gas.
• Questionable Contribution to SDG 7 (Affordable and Clean Energy): While the biogas produced is a source of energy, the process is not without environmental trade-offs. The study notes the potential for “pollution swapping,” where the reduction of one pollutant leads to an increase in others, questioning the “clean” credentials of this energy source.

Conflicts with Health, Community, and Environmental SDGs

The research indicates that the widespread adoption of manure digesters, often supported by government subsidies, may actively undermine progress on several key Sustainable Development Goals by entrenching unsustainable agricultural models.

Key Findings on Adverse SDG Impacts:

1. Undermining SDG 3 (Good Health and Well-being) and SDG 11 (Sustainable Cities and Communities): The economic viability of digesters is greatest in large, industrial-scale livestock operations. Promoting this technology incentivizes a model of agriculture linked to significant public health risks for rural communities, including air and water pollution and increased potential for animal-to-human disease transmission.
2. Threatening SDG 6 (Clean Water and Sanitation) and SDG 15 (Life on Land): The technology can lead to “pollution swapping.” For example, while methane may be captured, emissions of ammonia can increase. Furthermore, toxic byproducts from biogas flaring and other pollutant releases can contaminate local water sources and ecosystems, directly opposing the objectives of clean water and protecting life on land.
3. Contradicting SDG 12 (Responsible Consumption and Production): By subsidizing a technology that props up an industrial agricultural system, policymakers may miss opportunities to invest in more holistic and genuinely sustainable production systems. The focus on digesters represents a narrow, end-of-pipe solution rather than a systemic shift towards responsible production as envisioned by SDG 12.

Conclusion: A Misalignment with Sustainable Development Objectives

The Johns Hopkins study concludes that manure digesters should not be promoted or subsidized as a pro-environment or pro-public-health technology. The evidence suggests they are not a meaningful climate solution and may exacerbate environmental and public health problems, thereby conflicting with the integrated nature of the Sustainable Development Goals. Focusing on such technologies risks creating a false sense of progress, diverting attention and resources from more effective strategies to achieve a sustainable and healthy food system.

1. Which SDGs are addressed or connected to the issues highlighted in the article?

The article on manure digesters touches upon several Sustainable Development Goals by discussing the technology’s impact on the environment, energy production, public health, and agricultural practices. The following SDGs are relevant:

• SDG 3: Good Health and Well-being – The article discusses public health hazards to rural populations, including air and water pollution and disease transmission associated with industrial-scale agriculture, which is incentivized by digesters.
• SDG 6: Clean Water and Sanitation – The text mentions the risk of water pollution from large livestock operations, which are promoted by the economic model of manure digesters.
• SDG 7: Affordable and Clean Energy – Manure digesters are presented as a technology that produces “biogas,” a source of energy, positioning them within the clean energy discourse.
• SDG 12: Responsible Consumption and Production – The core topic is the management of agricultural waste (manure), which directly relates to sustainable waste management practices.
• SDG 13: Climate Action – The primary justification for manure digesters discussed in the article is the reduction of greenhouse gas emissions, particularly methane, to combat climate change.

2. What specific targets under those SDGs can be identified based on the article’s content?

Based on the issues discussed, several specific SDG targets can be identified:

1. SDG 3: Good Health and Well-being

   • Target 3.9: By 2030, substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination. The article raises concerns that digesters may lead to “pollution swapping,” increasing ammonia emissions and releasing toxic byproducts, which pose health risks to nearby rural populations.

2. SDG 6: Clean Water and Sanitation

   • Target 6.3: By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials. The article implies that by incentivizing industrial-scale agriculture, digesters may indirectly contribute to water pollution risks associated with such operations.

3. SDG 7: Affordable and Clean Energy

   • Target 7.2: By 2030, increase substantially the share of renewable energy in the global energy mix. The article evaluates the claim that biogas from manure digesters is a “renewable source of energy,” directly connecting to this target.

4. SDG 12: Responsible Consumption and Production

   • Target 12.4: By 2020, achieve the environmentally sound management of chemicals and all wastes throughout their life cycle… and significantly reduce their release to air, water and soil in order to minimize their adverse impacts on human health and the environment. The article critically examines manure digesters as a method for managing agricultural waste (manure) and questions their environmental soundness due to “pollution swapping.”

5. SDG 13: Climate Action

   • Target 13.2: Integrate climate change measures into national policies, strategies and planning. The article mentions that the adoption of digesters is supported by “state and federal financing and subsidy programs” as a climate solution, which is a direct example of this target in action. However, the research questions the effectiveness of this policy.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

The article mentions or implies several quantitative and qualitative indicators that can be used to measure progress and evaluate the effectiveness of manure digesters in relation to the identified targets.

• Greenhouse Gas Emissions Levels: The article explicitly states that “methane emissions from untreated manure only accounted for about 11% of total U.S. agricultural greenhouse gas emissions.” It also mentions potential increases in “nitrous oxide, another potent greenhouse gas.” Measuring the net change in methane and nitrous oxide emissions from farms using digesters is a direct indicator for climate action (SDG 13).
• Air and Water Pollutant Levels: The text refers to “ammonia emissions, toxic byproducts from biogas flaring, and other pollutant releases into the environment.” Monitoring the levels of these specific pollutants in the air and water around facilities with digesters would serve as an indicator for public health (SDG 3.9) and clean water (SDG 6.3).
• Share of Renewable Energy from Biogas: The article discusses biogas as a “source of energy.” The amount of energy produced from biogas and its percentage contribution to the local or national energy grid would be an indicator for the renewable energy target (SDG 7.2).
• Number and Scale of Digester Adoption: The article provides a specific number: “460 manure digesters were in use or under construction on farms in the U.S. as of June 2024.” This number, along with data on the size of the livestock operations they serve, acts as an indicator of the implementation of this waste management technology (SDG 12.4) and the scale of agriculture being incentivized.
• Amount of Government Subsidies: The article notes that digester adoption is supported by “state and federal financing and subsidy programs.” The total monetary value of these subsidies is an indicator of policy integration and government investment in this specific climate change measure (SDG 13.2).

4. Create a table with three columns titled ‘SDGs, Targets and Indicators” to present the findings from analyzing the article.

Source: publichealth.jhu.edu