I am Alexis Samson, a sophomore agricultural engineering major at the University of Nebraska-Lincoln where I work for Dr. Amy Schmidt (aka the Manure Lady). Even though I’ve been working for THE manure expert in Nebraska for nearly two years, I know I still have a lot to learn in the world of manure management.  Fortunately, I was able to take my manure knowledge to the next level this year by attending the Waste to Worth Conference hosted by the Livestock Poultry and Environmental Learning Community (LPELC), a nationwide team of university extension professionals specializing in addressing environmental impacts of livestock production. The event turned out to be a great experience where I got to meet so many other Turd Nerds and see what they have all been working on.

One of the manure related topics that I knew nothing about beforehand and really interested me was anaerobic digestion (AD). Digestion was a hot topic at the conference this year, it was the topic of numerous presentations and came up in casual conversations as well. Obviously, I’ve not become an expert on AD overnight – but I found it really interesting and wanted to share a few highlights of what I learned that could benefit Nebraska farmers who might be interested in this technology as well. 

One of the manure-related topics that I knew nothing about beforehand and really interested me was anaerobic digestion (AD). Digestion was a hot topic at the conference this year, it was the topic of numerous presentations and came up in casual conversations as well. Obviously, I’ve not become an expert on AD overnight – but I found it really interesting and wanted to share a few highlights of what I learned that could benefit Nebraska farmers who might be interested in this technology as well

Anaerobic Digestion

During anaerobic digestion, organic waste (like manure or food scraps) is put into an airtight reactor where microorganisms break down the carbon in the waste and transform it into biogas. At the same time everything else in the “waste” material (like nitrogen, phosphorus, and salts) is condensed into a nutrient-rich sludge – this is called digestate. Digestate is typically spread on fields as a fertilizer after the anaerobic digestion process is complete. Building and maintaining digestion reactors requires a delicate balance of elements. You need a warm temperature, no oxygen, food for the microbes, and space for the process to occur. If all these conditions are met, the reactor should be able to produce biogas successfully. At the Waste to Worth conference, I heard from several farmers and researchers working to improve AD methods focusing on the cost effectiveness of digestors for a wider variety of operations and continuing to improve gas production and other impacts. 

Farm Size & Food Waste Impacts

Currently, digestors in the US are primarily located on large-scale livestock operations. They are expensive to install and come with sizeable operation and maintenance costs. It is difficult for many small farms to produce enough biogas energy to be able to outweigh these costs. Lauren Ray, an extension associate from Cornell University presented her work on trying to improve the economic feasibility of AD for smaller farms by identifying better stock material mixes from local community sources of food waste. The farmers she was working with found that local businesses and even individuals were willing to pay to dispose of their food waste, so producers were able to benefit financially from taking their waste and adding it to their digestor. This made the digesters more economically feasible especially for small farmers who were not producing a substantial amount of manure but were close to towns or cities. 

This study was done with New York dairies, but the data can help guide livestock producers in Nebraska. She found that for small, 300-cow dairies, the installation of an AD system was only realistically possible if the material being digested was 50% food waste. If the size of the dairy increased to 1,000 head, purchasing a digestor could be possible with only 25% food waste. The specifics, of course, vary with different energy prices and tipping fees (income from taking in food waste), but the main idea here is that if you have a small operation and are very interested in purchasing an AD system, the best way to mitigate the cost is to find a group nearby who is willing to pay you to take their food waste! Additionally, larger operations can still do the same and further increase their profits. Read more about her presentation:

Economic feasibility of dairy manure and food waste co-digestion at small, medium, and large farms.

System Cost vs. Return

Another topic I learned a lot about at the conference was the different possible end products of digestion and the possibilities of generating extra income for the user. While all digesters produce biogas, there is a big difference between this biogas and commercially available renewable natural gas (RNG), which people use to heat their homes or cook food. Biogas coming from digesters is a mix that contains carbon dioxide and hydrogen sulfide, in addition to methane fuel. In the past, these impurities meant that the product of digesters was typically burned on farm to heat barns (and the digester itself), or to produce electricity which could be sold to the local utility. However, the technology to transform biogas to RNG is improving and more efficient, such that some operations have incorporated the purification step so they can sell RNG directly to local homes or businesses.

One presentation by graduate student Luke Soko from Iowa State University examined the system costs and emission reductions from renewable natural gas (RNG) production, compared to traditional electricity generation via biogas, or even biogas flaring – all methods for reducing methane released and consolidating organic waste. His assessment found that the emission reduction from RNG and electricity production are closely comparable, both being highly effective methods of reducing greenhouse gas emissions from livestock production.  They also found that producers can typically get more money for selling renewable natural gas than selling electricity. However, biogas flaring was ultimately the most cost effective in mitigating harmful emissions if the only concern is greenhouse gas emissions. Read more about his presentation:

Bang for Your Buck: Developing Effective Anaerobic Digestion Policies for Carbon Emission Reduction.

New Learning Every Day

These are just two examples of new and exciting things being studied in the world of manure management. All over the country, extension experts and researchers are working hard to find new and creative ways to deal with manure in an environmentally conscious way. I hope that I was able to inspire some readers with a little bit of my interest in anaerobic digestors and to think about ways they can reduce emissions in their own homes, businesses, or farming operations. I am taking away from this year’s conference a better awareness of the scope of topics involving manure and am so happy to have a job where I can be exposed to so many impactful topics. I hope to attend again soon!