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Unlocking the Potential of Anaerobic Digesters

June 25, 2009

Source: Shutterstock, Phillip MinnisThe recent floods along the Red River focused the nation’s attention on yet another natural disaster. They also galvanized and united communities up and down the Red as they battled to save their homes and communities from destruction.

While watching from afar through the convenience of live televised coverage, I was truly amazed at the teamwork evident throughout each community as residents and volunteers worked together, filling sandbags, forming “sandbag brigades” to move the bags by hand to existing levees, then placing each sandbag, one by one, to raise walls of protection along the cresting Red. In many ways these heroic efforts seem an apt metaphor for the work and approach needed to address greenhouse gas emissions. Not only will the work of addressing climate change require all members of the community to commit to and pursue a unified goal, it will take coordination, vision, and planning to ensure that the work is completed as effectively and efficiently as possible and that the work of many is not wasted because of a failure on the part of leaders to raise the levees along an ignored stretch of the river.

Widespread introduction of anaerobic digesters across animal agriculture has the potential to greatly reduce nutrient and pathogen runoff, while also eliminating up to a third of the greenhouse gas emissions credited to agriculture.

This shortsightedness in flood management is akin to fighting to reduce greenhouse gas emissions in certain sectors like automobiles while ignoring the emissions from other sectors like farm waste management. A full 14% of U.S. greenhouse gas emissions come from agriculture, yet most—if not all—attention is focused on large-scale electric power generation (32%) and transportation (25%). So even if transportation emissions are cut in half over the next 20 years, the continuation and probable growth in emissions from the agricultural sector will overshadow any gains.

It’s from this perspective we must ask, How will we address agricultural emissions? While we have multiple policy paths ranging from a strict regulation of greenhouse gases from the agricultural sector to a more lax support for voluntary efforts to curb emissions, the first and more important issue to resolve is determining how we will curb emissions. Then we can help state legislatures and Congress figure out how to get there.

One solution that deserves more consideration is the widespread implementation of anaerobic digesters. Digesters act as big cooking pots where manure and other organic waste is heated in a sealed tank. The heat allows bacteria to break down the waste, effectively pulling off the methane in the sealed tank. Then the methane can be burned in an engine to create electricity. The electricity produces very few emissions, is renewable, and has the added benefit of dispatchability—it can be turned on and off when needed, unlike wind or solar.

Methane from animal waste poses a considerable source of emissions, and has 20 times the greenhouse gas impact of carbon dioxide. Moreover, animal waste causes a number of other environmental and human health issues. When undigested manure is applied to land it releases ammonia in a gas form. Undigested manure also contains potassium, nitrogen and phosphorous vital to plant growth. Unfortunately it is often difficult for plants to obtain the nutrients from undigested manure, creating widespread potential for runoff into waterways. Animal waste runoff contributes to the Gulf of Mexico “Dead Zone,” an area roughly the size of New Jersey located at the mouth of the Mississippi River that is inhospitable to aquatic life. Excess nutrients contribute to the growth of algal blooms, and when they die oxygen is used to decompose the algae, creating hypoxic conditions. This uses up the oxygen that would otherwise be consumed by aquatic life. Along with these nutrients, undigested manure also contains pathogens that can harm wildlife and humans if released into waterways.

Fortunately, technology exists that not only provides a clean energy source, but resolves or greatly reduces the problems of nutrient release into waterways. Digesting manure allows it to more readily release nutrients to plants, greatly reducing the potential for nutrient runoff into waterways. Digested manure also kills over 99% of all pathogens, almost entirely eliminating the risk of introducing pathogens such as ecoli and cryptosporidium into our water supply.

Widespread introduction of anaerobic digesters across animal agriculture has the potential to greatly reduce nutrient and pathogen runoff, while also eliminating up to a third of the greenhouse gas emissions credited to agriculture. Couple that with the role digesters could play in creating clean, renewable energy and eventually displacing fossil fuel power with its high greenhouse gas emissions, and you get a double impact in reducing greenhouse gases—once in the agricultural sector and again in the electric sector. Addressing greenhouse gases in the agricultural sector is just as necessary to reducing total greenhouse gas emissions as it is to sandbag along the entire length of a flooding river. In fact, the strategy of addressing agricultural greenhouse gas emissions through digesters is like putting down sandbags twice the size of traditional sandbags, making it much easier to achieve our collective goal of containing a flooding river of greenhouse gas emissions.

The Conservation PlannerThis article is from the June 2009 issue of The Conservation Planner, a publication of The Minnesota Project. Click here to download the entire issue and explore past issues >>
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