Several essays in this series have highlighted some very high-tech methods developed and deployed to monitor the state of the global environment. From super-sensitive satellites to programmable ocean buoys, the ingenuity of the community of environmental scientists, engineers and technicians is impressive. It is fascinating to sit back and marvel at what we know and how we know it as we watch our environmental future unfold at very high resolution and in real time.
As much as I enjoy following this crucial and challenging area of science, I have no active role to play in the projects that I have covered so far in these essays. Contributions to solving our environmental issues can also be made through a more local and personal process of exploration and experimentation, for example, in the development and application of technologies that are lower-tech and applicable closer to home.
So in this essay, I’d like to step away from the presentation of our high-tech tools and talk about my last research project, and a very low-tech approach to making a dent in the environmental footprint of agriculture. There is a personal context for this last project as well, making it something of an end-of-career, closing-the-circle event.
Coming of age in the ‘60s and 70s, I experienced that early wave of global environmental awareness that included a major focus on getting “back-to-the-land.” The Last Whole Earth Catalog, Mother Earth News and projects like The Ark at the New Alchemy Institute on Cape Cod gave visibility to the concept of self-sufficiency and low environmental impact. I was a big fan of Helen and Scott Nearing and read all about their self-sufficient, house-building, homesteading experiments in Vermont and Maine. I even wrote to them once and still have the letter received in response from Helen Nearing.
Environmental awareness and activism were heightened by the First Earth Day in 1970 – a topic of a previous essay. While inspired by the Nearings and that first Earth Day, my career went in a more traditional direction, and I spent 40 years studying and teaching mostly about forest ecosystems in a global context.
In 2007, at the end of a 4-year stint in administration at my home institution, the University of New Hampshire (UNH), I was ready to return to a primarily teaching role when a colleague, Tom Kelly, urged me to write a proposal to a USDA grant program called SARE (for Sustainable Agriculture Research and Education). USDA was about the only federal agency I had never applied to before and success seemed unlikely. But a focus in this innovative research program on farms as integrated agricultural ecosystems led to an award that funded 10 years of work at another innovative institution, the Organic Dairy Research Farm at UNH – the only one of its kind at a land grant university in the USA.
As the project developed, a chance encounter with Brian Jerose of Agrilab Technologies in Vermont, and the generosity of an anonymous donor, led to a focus on generating and capturing heat energy from organic farm wastes by a “new technology” called aerated static pile composting. More on this in a moment, but let’s close the personal circle here first.
The final report from the project credits folks at New Alchemy and other innovators for inspiring a life-long interest in closing cycles and minimizing environmental impacts. Reports out of New Alchemy authored by Gary Hirshberg, founder of Stonyfield Yogurt, and Bruce Fulford, Principal of City Soil (a leader in urban composting), both of whom were part of New Alchemy in the early days, provided most of what little had been written on using compost as a source of heat in greenhouses. Stonyfield and the Hirshbergs were early supporters of the UNH Organic Dairy, and Bruce Fulford served as research adviser to Matt Smith, a Ph.D. student who basically ran the project I am about to describe, so they provided inspiration and support both at the beginning as well as the end of this personal career circle.
Being so far removed from all of my previous research on forests, this final project began as something of a lark. A fun way to round out a research career and pursue a personal interest in renewable energy and agriculture. It became more than that. With excellent guidance from the people at SARE, especially Vern Grubinger, David Holm, and Kathleen Newkirk and excellent graduate and undergraduate students, like Matt Smith, Allison Leach, Nicole Williamson, Dena Hoffman, Gabriel Perkins and Amy Lamb, it became an experimental journey into a new method of processing organic wastes and generating usable heat. Support from the New Hampshire Agricultural Experiment Station was crucial throughout the project.
The potential importance of the research also came into focus for our team. It turns out that composting is a growth industry, at least in New England. Several states are imposing new limitations on the amount of organic wastes that can be shunted to landfills. The best alternative treatment for these wastes is composting, and aerated static pile composting is rising as a standard method. And there are non-food sources of organic wastes as well. The aerated static pile method was actually first developed by the USEPA in the 1980s as a method for treating sewage sludge before disposal, so the range of applications extends well beyond agricultural wastes, and there is lots of material available. Imagine turning this waste stream into an energy resource.
Our task, then was to test the value of adding a method for capturing and using the heat and gases produced by aerobic (with oxygen) decomposition of organic wastes. The UNH Organic Dairy Research Farm was a perfect incubator for this research. How much energy could be produced? What was the best use of this energy?
So now it is time to answer this question: what is aerated static pile composting? When I mention composting one of two images tends to be generated in the minds of my conversational partners. The first would be traditional backyard-style compost piles that need turning and tending and can take two years to complete the decay process. There are commercial versions of this approach that are faster, but the process is one that has been known and used for as long as humans have generated agricultural wastes.
The second is the newer approach to generating methane (or biogas) by anaerobic digestion – decomposition in the absence of oxygen, with methane (as in natural gas) as the major product, but with carbon dioxide and other gases present as well.
Each of these two methods has important limitations.
Traditional composting takes time and space. Regulations vary, but in general, the material needs to be kept above 130 degrees Fahrenheit for several consecutive days before it can be sold as a commercial product for use in farms and gardens.
UNH has run an innovative program for composting food wastes from the dining halls for over 30 years. The material is mixed with barn waste from the equine facility and laid out in windrows that occupy a couple of acres of land. The piles are turned every couple of weeks and are ready for spreading in about 2 years. The investment in time, labor and space is considerable, and the only product is the compost.
UNH made one early foray into anaerobic digestion, which was not successful. This is not an uncommon outcome. After substantial investments into research on the process, there are relatively few systems that have achieved successful long-term operation, and most of these are on large farms. An EPA data base lists 272 operating digesters, with 61 additional facilities under construction. About 80% of these are on dairy farms (there are about 40,000 dairy farms in the USA). While this is a controversial topic, most reports emphasize that this complex technology is not cost-effective without external grants from state or federal programs. Of the systems in the EPA database, 108 have received USDA grants.
An advantage of this anaerobic process is that the first product is biogas (about 70% methane and 30% carbon dioxide with some important impurities as well) which can be used in a number of applications, and can be piped from one location to another. However, the process results in very incomplete decomposition, and while the residue can be spread on farmland, the material is not necessarily pleasant to handle, and with the mixture of gases in the product, it burns less efficiently than pipeline natural gas, and can require further purification for some applications.
So if aerated static pile composting is neither of these, then what is it?
The key words are aerated and static. Once a pile is created, it does not have to be turned. So how then does it remain aerobic (with enough oxygen to support the microorganisms that break down the material)? It is the lack of oxygen that leads to the nasty odors often associated with composting or untended piles of rotting farm wastes. The simple but essential piece added to the process is perforated tubing (as in leach field pipes for septic systems) placed under the material. The tubes are then attached to a fan that draws air down through the pile at a rate that maintains oxygen content without cooling the pile. Here is a conceptual diagram of the process. The UNH media folks have produced a wonderful video explaining the concept, using the Organic Dairy system as an example.
This sounds simple, and it is. The method can be set up in a variety of ways from the most basic to large and complex: it is scalable. A schematic for a very basic system is included at the end of this essay. With the support of our donor and the University’s Agricultural Experiment Station, UNH constructed a research-scale facility complete with sensors for measuring heat production and concentrations of several gases in the exhaust vapor produced. UNH builds everything to a 75-100 year standard, so the building itself is very high quality (as you can see in these images), and the instrumentation added to the expense.
Inside this structure is a concrete floor with shallow trenches holding perforated leach field pipes that connect through a headwall to the fan and heat exchanger. The fan draws air down through the pile and into the heat exchanger. Timing and amount of airflow are optimized to balance aeration with minimal cooling of the pile. There is a lot more detail on this process in the report from the project. Brian Jerose at Agrilab Technologies was the guiding light in the design and implementation of this facility. Matt Smith made it work.
The UNH Organic Dairy Research Farm houses about 100 Jersey cattle with 40-50 milkers at any one time. As an organic dairy, the milkers spend significant amount of time on pasture, but are in the barn much of time as well. During this project, the barn was a bedded pack system, meaning that wood shavings were used to absorb wastes. The resulting mixture of manures and wood shaving bedding, amounting to hundreds of tons per year, was transferred to the composting facility, which could process all of this waste produced on the farm.
So how much energy was produced? In production mode, temperatures in the pile could reached 150 degrees Fahrenheit and the facility, when fully loaded, could generate up to 4,000,000 BTU of heat energy per day. For comparison, a State of Massachusetts site estimates home heating requirements during the heating season at about 170,000 BTU/day. The process released about 40% of the carbon in the material as carbon dioxide, with about 60% of the initial material remaining as compost. Time required to produce usable compost could be as short as three weeks
There was never a significant amount of methane in the exhaust gas. This is crucial, as methane is ~ 25 times more effective as a greenhouse gas than carbon dioxide. Releasing the carbon as carbon dioxide instead of methane is a major advantage of aerated composting. Applying finished compost to fields also leads to the formation of humus and the long-term storage (or sequestration) of the carbon in the material.
The major limitation with capturing and using heat from the aerated static composting process is that, unlike biogas, heat cannot be transported over significant distances. In addition, research from the UNH facility highlighted that storing the generated heat for later use also reduced efficiency. The best use was an immediate heating application.
While the comparison with home heating demands might be interesting for perspective and scale, this is not a likely application! So, let’s put this into the context of crop production in a farm setting. UNH maintains a number of permanent greenhouses and also several what are termed high tunnels – temporary greenhouses with plastic covers. The use of greenhouses and high tunnels is expanding rapidly in New England as increasing farm-to-table and local food production, sparked by consumer demand, reshapes the food system in the region.
To borrow a phrase from the food industry, it would seem that our composting process and greenhouse crop production are a natural pairing! The epilog to our final report for the project described several locations where UNH could reduce heating costs and extend the growing season on its experimental farms by utilizing dining hall and equine facility wastes to heat those structures.
Given the rates of organic waste generation, and assuming direct transfer of heated exhaust gases to those structures, without intermediate storage, as many as 5 high tunnel structures might be heated year round in this manner, displacing fossil fuels that are now used. The image above is a conceptual example of how this combination might look. Remember that UNH is already maintaining traditional compost piles for these same wastes. Without the need for turning the material, this approach could save labor in addition to fuel.
There is even more potential here for increasing crop production. The exhaust gas is rich in carbon dioxide which can fertilize crop growth, as well as being saturated with water vapor. Some engineering would be involved in tapping these resources, however, as the vapor also contains concentrations of ammonia that would be toxic to plants. One phase of the project tested a simple biofilter made of wood chips and compost that reduced ammonia concentrations in the exhaust gas to acceptable levels.
Our work at the UNH Organic Dairy research Farm has come to an end, but applications of this approach continue. Brian Jerose and colleagues at Agrilab Technologies, who were the first to build heat capturing systems and were the design source for our system, continue to refine and apply this technology in a variety of situations.
Perhaps there is a future for this pairing of technologies that recycles the carbon in organic wastes into new crop production and long-term storage of carbon in humus (or soil organic matter). The multiple reductions in climate change impacts of agriculture seem worth pursuing.
This essay has repeated some of the themes from an earlier post on Earth Day 1 and Earth Day 51, and on a career that has been allowed to come full circle, concluding with work on a technology that can reduce greenhouse gas emissions and enhance local food production. That last image above of the linked composting/greenhouse system can be traced conceptually back to the Ark and to the New Alchemy Institute. A newer realization of an older concept!
Sustainable management of ecosystems, including agricultural ecosystems, is all about closing cycles and reusing resources. This project has closed a personal intellectual cycle as well.
Sources
Two of the early Nearing books are here:
The New Alchemy Institute website is here:
http://www.thegreencenter.net/ See especially the page on Bioshelters and Arks
A recent article on the history and current work at New Alchemy is here:
The Earth Day essay from this series is here:
Information on City Soil and Bruce Fulford can be found here:
http://citysoil.org/index.html
Gary Hirshberg is a continuing source of inspiration for me and an eloquent proponent of healthy and socially responsible food systems:
https://hirshberginstitute.com/gary-hirshberg/
https://en.wikipedia.org/wiki/Gary_Hirshberg
Information on the New Hampshire Agricultural Experiment Station and the Organic Dairy Research Farm are here:
https://colsa.unh.edu/facility/organic-dairy-research-farm
The Sustainable Agriculture Research and Education (SARE) Program is described here:
https://www.sare.org/
The video on the aerated static pile composting facility and process is here:
https://www.unh.edu/unhtoday/2016/11/composting-unh-organic-dairy-research-farm
The final report from our SARE project is here:
and also at the UNH Scholars Repository here:
https://scholars.unh.edu/faculty_pubs/921/
Here are some references on anaerobic biogas production and the number of dairy farms using this process:
https://smallfarms.cornell.edu/2013/06/anaerobic-digesters/
https://thecounter.org/misbegotten-promise-anaerobic-digesters-cafo/
https://www.epa.gov/agstar/livestock-anaerobic-digester-database
https://hoards.com/article-22687-dairy-farm-numbers-hover-near-40000.html
Information on heating costs for a home in Massachusetts is taken from here:
https://www.mass.gov/info-details/household-heating-costs#factors-impacting-heating-prices-
The Extension Program out of UNH maintains this site covering aspects of high tunnel crop production
https://extension.unh.edu/agriculture-gardens/fruit-vegetable-crops/high-tunnel-production
Brian Jerose and Agrilab Technologies are the best source for information on building aerated static pile composting systems. This site includes several active locations and projects:
https://agrilabtech.com/
A comprehensive review of the history of heat capture from composting is here:
Matthew M. Smith, John D. Aber & Robert Rynk (2016): Heat Recovery from Composting: A Comprehensive Review of System Design, Recovery Rate, and Utilization, Compost Science & Utilization, http://dx.doi.org/10.1080/1065657X.2016.1233082