Manure and Energy

Description of Event

Manure from a dairy farm powering light.

Stimuli: How will students experience and/or observe the phenomena/problem?

The stimuli here would vary based on where in the story/where in the science, someone would like to start.

Possible starting points:

1. How does a dairy produce and sell electricity with the energy from cows?

2. How is electricity produced from cow manure?

3. What is happening in the digester/how does the collected waste generate electricity?

https://manure.ucdavis.edu/Illustrations/Dairy_Lagoons/

2:05 - 3:50

https://youtu.be/O1JjaWFOA60

Essential Questions:

How can cow manure be transformed into electrical power? (You could also use mechanical or thermal energy if you replaced “light” with a furnace, fan, generator, etc..)

Related Phenomena/Problems:

• Generation of energy from food waste

• Other energy sources/generation and transfer of one form of energy to another: wind, solar, hydroelectric

• Natural gas production from food waste

• Farting, the concept of lighting a fart on fire

Considerations for Instructional Design:

• Students can calculate the approximate volume of manure a dairy cow produces in one day and the relative space required to store it. 

• Students could consider food waste as a related engineering problem and compare/contrast solutions. 

• Students could generate natural gas using blended fruits. They could measure the gas produced and transform the energy to thermal power by lighting it. (BBC Earth Lab, 2023)

• Students can investigate and have productive conversations about: 

  • microbial action in the process of decomposition

  • issues related to the production of biogas and its disruption to the biosphere

  • engineering design and the development of mini digesters as a solution to treating the biogas problem. 

• Students could look specifically into the different populations of microorganisms used in methane digesters.

• Students observe large scale aerobic digesters that have been built to break down different types of food waste with microbes. What do they notice? What do they wonder?

• Throughout the course of a unit, students could work toward the development, construction, and data collection of their own digesters.

• An extension of this phenomenon, which would cross into more physical science, would be answering exactly how the gas captured runs the engine to the generator.

• A further extension into physical sciences may be how a generator takes the energy from gas and converts it to electrical energy.

   

Explanation:

What is methane? 

Methane is an odorless gas composed of carbon and hydrogen. It’s noted as CH4 because each methane molecule contains one carbon atom surrounded by four hydrogen atoms. Methane is a naturally occurring, organic compound.(Werth, S. 2019)

Cattle are part of the biogenic carbon cycle:

Like water and nitrogen, carbon is recycled into and out of the atmosphere in a natural cycle. You can see this illustrated in the diagram above. Carbon cycles from the atmosphere to plants through photosynthesis and plants to the animals that consume the plants. The waste from animals is broken down and the carbon is returned to the atmosphere where the cycle repeats.

Animals, including humans, consume the carbon/carbohydrates from plants as part of their regular diet. However, there are some plants that store their carbon/carbohydrates in a type of plant fiber called cellulose. Most animals, including humans, cannot digest cellulose and, therefore, cannot utilize the carbohydrates found in cellulose. Cellulose is found in plants such as mature grasses.

Cattle, and a few select animals with similar digestive systems, can digest cellulose because their digestive systems contain microorganisms that assist in breaking cellulose into simpler carbohydrates. This means they can recycle those carbohydrates by using them to generate energy for themselves via the process of fermentation. The left-over simple carbohydrates can be utilized by animals, including humans. Consuming the carbohydrates in cow’s milk is a prime example of this.

The microorganisms in cattle's digestive systems produce gas and break down cellulose. Cattle burp the methane/carbon back into the atmosphere. When cattle poop, there are still carbohydrates that are being broken down. In the process of manure decomposing, methane is also produced and released back into the atmosphere. Methane in the atmosphere is eventually converted into carbon dioxide through hydroxyl oxidation in the atmosphere, then returns to plants as carbon dioxide during photosynthesis, and the process begins again. (Werth, 2020) (HS-LS2-3) 

Methane is also a greenhouse gas:

Greenhouse gases are gases in the atmosphere that trap heat. Carbon dioxide and methane are the two most abundant greenhouse gases in our atmosphere. Carbon dioxide makes up about 80% of greenhouse gasses and takes thousands of years to break down/make its way back through the carbon cycle. Methane makes up roughly 12.5% but breaks down in about 12 years. Methane is concerning because pound-for-pound methane is more than 25 times more potent than carbon dioxide at trapping heat in the atmosphere over a 100-year period. (IPCC, 2013) (HS-ESS3-6) (HS-ESS2-4) (HS-ESS2-2)

Uninterrupted, this cycle is efficient, but…

The biogenic carbon cycle has been able to keep up with recycling its greenhouse gases at a rate that was not causing significant global warming. What’s not accounted for in the biogenic carbon cycle are the vast amounts of carbon stored deep within the earth in the form of fossil fuels. Historically, this carbon was not released into the atmosphere in significant amounts. This changed as many humans currently depend on fossil fuels and are burning them for energy/power to run everyday processes and machines. It is this extra carbon that is burned and then released as greenhouse gases into the atmosphere that disrupts the cycle. Currently the biogenic carbon cycle cannot recycle carbon (remove it from the atmosphere) fast enough. As a result, there are more greenhouse gases in the atmosphere, trapping heat. (Werth, S. 2019)

Global warming affects everyone:

The result of the excess greenhouse gasses in Earth’s atmosphere is contributing to global warming. This is a problem people want to solve. Global warming impacts everyone, including dairy producers. Dairy cattle provide a nutrient-dense product (milk) to feed the world, but they cannot do that without high-quality nutrition sources fueling their bodies. Cattle rely on healthy and diverse pastures to produce quality milk. In turn, plant species need specific environmental conditions to grow, and those conditions can be altered by global warming quicker than plants can adapt.

Engineering solutions:

Dairies have a lot of manure to manage. Unmanaged, manure can endanger soil, waterways, or surrounding ecosystems. Lagoons are a common method used to manage manure. Lagoons are lined ponds or collection areas that prevent manure from leaching high amounts of nitrogen and phosphorus into the ground and provide a space where the manure can be using microorganisms to break down the waste.

A “dairy digester” is a recent engineering solution that dairy owners can use to lower methane emissions from manure.

What is a dairy digester?

The digester is an enclosed container that utilizes complex microbial populations to break down the organic matter of the manure in the absence of oxygen. As the microorganisms digest the manure, they produce methane. The digester is sealed to keep oxygen out and to trap the methane for storage. Manure, food waste, energy crops, crop residue, and fats can be combined to increase the amount and rate of gas production inside the digester. The methane produced by a dairy digester can run an on-farm generator, be sold to a local utility, be sold as renewable energy credit, or be injected into natural gas pipelines as renewable natural gas (RNG). With the help of these dairy digesters, methane produced by cattle can help neutralize the climate rather than add additional warming to the atmosphere. (HS-ESS3-2) (HS-ESS3-4) (Environmental Protection Agency, 2022). (HS-LS1-6)

Below is a simplified diagram depicting the path of cow manure from barn to digester to gas storage to energy generation. Also depicted are the liquids and solids that are separated out of the digester, processed, recycled, and used as bedding, as compost, or as liquid fertilizer.

(Heller, Mark. 2022)

How does a digester work?

Note: At this point, the complexity of the metabolic processes generally goes beyond the scope of the high school-level disciplinary core ideas. In general, complex organic matter (manure) is broken down by hydrolysis into sugars, lipids, and proteins. Those are digested in the absence of oxygen. The digested molecules are used to generate energy for the microorganisms via fermentation. These details and many more can be seen in the diagram below.

(Zhiqiang Zhao, 2020)

Student and teacher generated questions about this phenomenon/problem that could be instructionally productive:

About cattle digestion:

• What is it that a cow is eating?

• Do you need special cows?

• How does a cow's stomach work?

• Don't they just milk the cows?  

• How does the carbon cycle relate to cow poop?

• What type of gases does a cow produce when digesting food?

• How can poop become energy?

How a dairy digester works – management:

• What is a dairy digester?

• What other inputs are needed?

• How much does it cost?

• Will they ever move to human waste?

• How big of a turbine do you need? 

• How much money will I make?

• Is this something we could try at our school farm?

• Do you need special equipment?

• How is it transported?

• Is this process dangerous?

• Is the technology long-lasting, or are updates/upgrades required?

How a dairy digester works – technology:

• How does the dairy digester technology work?

• How do you store the manure?

• Is this process poisonous?

• Can any farmer take part in this?

• What is biogas?

• What is a natural gas?

• Is the natural gas harmful?

• How much energy can be produced?

• Will it smell bad?

• How much can be converted?

• How quickly does it break down?

• How widely available is this technology?

• How is everything added? 

About this as a renewable energy:

• What can we do to assist with this technology?

• How many farmers need to adopt this technology to make a true impact?

• Are there any differences between obtaining energy from solid wastes and fossil fuels?

• How does it reduce the carbon impact?

• How would it be integrated into the energy grid?

• What is a carbon footprint?

• What are the by-products of the process, and can it harm other parts of the environment?

• What is the carbon footprint of dairy farms?

• Can we use the gas to run our cars?

• How would this help our future generation?

Explaining the phenomenon/problem or related phenomena could lead students toward developing the following DCIs:

LS1.C: Organization for Matter & Energy Flow in Organisms

As matter and energy flow through different organizational levels of living systems, chemical elements are recombined in different ways to form different products. (HS-LS1-6),(HS-LS1-7) The methane digester itself can demonstrate this concept by highlighting the path and products of manure (pre-manure and post-digestion). The gas produced in the sealed system that didn’t exist prior demonstrates recombination of matter and is the byproduct of the metabolic activities of the microorganisms. 

The biogenic carbon cycle builds toward this with the recombination of carbon with other elements, including carbohydrates that are utilized as energy at all levels of the food chain. Related, the concept of ruminants’ ability to digest energy and convert it to the carbohydrates in milk that humans can digest and utilize demonstrates the elements of carbohydrates being recombined into different carbohydrates.

As a result of these chemical reactions, energy is transferred from one system of interacting molecules to another and releases energy to the surrounding environment to maintain body temperature. Cellular respiration is a chemical process whereby the bonds of food molecules and oxygen molecules are broken, and new compounds are formed that can transport energy to muscles. (HS-LS1-7) For the digester, fermentation can be compared to cellular respiration. Additionally, the gas production, the heat produced, and the thriving of the microorganisms can serve as measurable evidence of these reactions and energy transfers.

LS2.B: Cycles of Matter & Energy Transfer in Ecosystems

Plants or algae form the lowest level of the food web. At each link upward in a food web, only a small fraction of the matter consumed at the lower level is transferred upward to produce growth and release energy in cellular respiration at the higher level. Given this inefficiency, there are generally fewer organisms at higher levels of a food web. Some matter reacts to release energy for life functions, some matter is stored in newly made structures, and much is discarded. The chemical elements that make up the molecules of organisms pass through food webs and into and out of the atmosphere and soil, and they are combined and recombined in different ways. At each link in an ecosystem, matter and energy are conserved. (HS-LS2-4) The biogenic carbon cycle provides a point to build an understanding of the chemical changes and recycling of molecules between the atmosphere, plants, soil and animals. The metabolism of the microorganisms (either in the rumen or utilized in the digester) and their relative populations per cow could serve as a foundation for understanding the magnitude of a few organisms at higher levels of the food web. The manure digester could be tied back to energy that was essentially discarded between different levels of the food chain.

Photosynthesis and cellular respiration are important components of the carbon cycle, in which carbon is exchanged among the biosphere, atmosphere, oceans, and geosphere through chemical, physical, geological, and biological processes. (HS-LS2-5) The digestor itself, considered in the context of the problem it is designed to help mitigate, requires understanding the recycling of carbon. Stepping back in context of how the problem has been created, integrates the carbon cycle in its entirety. The concept that carbon sequestered deep in Earth within fossil fuel reserves did not contribute to carbon levels in the atmosphere until they have been extracted and burned has the potential for some relevant sensemaking of interactions between geological and biological processes.

ESS3.A: Natural Resources

All forms of energy production and other resource extraction have associated economic, social, environmental, and geopolitical costs and risks as well as benefits. New technologies and social regulations can change the balance of these factors. (HS-ESS3-2) This is built toward understanding how carbon levels in the atmosphere have increased dramatically as a result of the use of fossil fuels spanning nearly all aspects of our students’ everyday lives. The dairy industry has many regulations to mitigate potentially negative environmental effects. Dairy owners must balance the costs, risks, and benefits of technologies such as digesters.  

ESS3.C Human Impacts on Earth Systems

The sustainability of human societies and the biodiversity that supports them requires responsible management of natural resources. (HS-ESS3-3) Responsible manure management by dairy owners keeps our soil, water systems, and surrounding ecosystems protected from harmful effects.  

Scientists and engineers can make major contributions by developing technologies that produce less pollution and waste and that preclude ecosystem degradation. (HS-ESS3-4) Manure management practices and regulations are designed specifically for the prevention of ecosystem degradation.

ESS3.D: Global Climate Change

Though the magnitudes of human impacts are greater than they have ever been, so too are human abilities to model, predict, and manage current and future impacts. (HS-ESS3-5) This builds toward the context of the biogenic carbon cycle and the effects of removing stored carbon (in the form of fossil fuels) that otherwise would not have much of an effect on the levels of greenhouse gases.

Notes about relevance and authenticity (funds of knowledge, interests, identity) Why might students be engaged?

• Poop as a renewable energy source is fascinating.

• Global warming and the concept of climate change are familiar to students.

• Students are growing up at a time when they are experiencing or hearing about extreme weather and weather-related events that correlate with the effects of global warming.

Resources/References 

BBC Earth Lab. GROSS! How to Make Methane Gas: Earth Lab. (23 August, 2016). Accessed 03 March, 2023. Available YouTube: https://youtu.be/jBtyUhiyp6Q 

Dawn E. Holmes, Jinjie Zhou, Jessica A. Smith, Caiqin Wang, Xinying Liu, Derek R. Lovley Different outer membrane c-type cytochromes are involved in direct interspecies electron transfer to Geobacter or Methanosarcina species 23 September 2022

EPA. (2 March, 2022). How does anaerobic digestion work? AgSTAR. https://www.epa.gov/agstar/how-does-anaerobic-digestion-work

Heller, Mark. (July 12, 2022.) ‘Cow power’ goes dark as manure-to-electricity fizzles. E&E News. Accessed April 18, 2023. https://www.eenews.net/articles/cow-power-goes-dark-as-manure-to-electricity-fizzles/

IPCC (2013) Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. [Stocker, T.F., D. Qin, G.K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.Environmental Protection Agency [EPA]. (2011, December). Recovering value from waste - Anaerobic digester system basics. AgSTAR. https://www.epa.gov/sites/default/files/2014-12/documents/recovering_value_from_waste.pdf

Rocha, A. (14 May, 2021). How handling manure waste from dairy cattle impacts greenhouse gas emissions and climate change. UC Davis CLEAR Center. https://clear.ucdavis.edu/explainers/how-handling-manure-waste-dairy-cattle-impacts-greenhouse-gas-emissions-and-climate

Rocha, A. (23 April, 2023). What is a dairy digester and how does it affect methane emissions?. UC Davis CLEAR Center. https://clear.ucdavis.edu/explainers/what-dairy-digester-and-how-does-it-affect-methane-emissions

United Nations [Pique Action] (2022, November 15.) Feeding Cows Seaweed to Reduce Methane, Symbrosia [Video]. YouTube. YouTube. https://youtu.be/ctragcEH1Y8 Zhiqiang Zhao, Yang Li, Yaobin Zhang, Derek R. Lovley,

Zhiqiang Zhao, Yang LiYaobin, Zhang, Derek R. LovleyAppels, et al. Anaerobic Digestion: Promoting Direct Interspecies Electron Transfer to Enhance Methane Production, iScience, Volume 23, Issue 12, 2020, 101794, ISSN 2589-0042, https://doi.org/10.1016/j.isci.2020.101794. 

Werth, S. (2020, February 19). The biogenic carbon cycle and cattle. UC Davis CLEAR Center. https://clear.ucdavis.edu/explainers/biogenic-carbon-cycle-and-cattle