Cow manure, also known as cow dung, is a byproduct of cows that can be a useful resource for generating renewable energy. As opposed to letting cow manure go to waste, energy recovery from this waste material provides environmental and economic benefits.
Why Cow Manure is a Good Source of Energy
Cows produce a significant amount of manure that contains high levels of organic matter such as undigested material from their feed. This organic matter contains stored chemical energy that can be harnessed and converted into useful energy forms.
Here are some key reasons why cow manure is an excellent candidate as an energy feedstock:
Abundant supply: There are over 90 million cows in the United States alone that generate over a billion tons of manure annually. This presents a huge amount of feedstock for energy generation.
High methane content: Cow manure contains considerable amounts of methane, the primary component of natural gas. Capturing this can be an excellent source of biogas.
Renewable: As long as there are cows, there will be a continual supply of cow manure. This makes it a sustainable and renewable energy resource.
Reduces waste: Energy conversion of cow manure mitigates its accumulation as a waste product. This promotes environmental stewardship.
Methods to Generate Energy from Cow Manure
There are several proven methods and technologies that allow harnessing the energy potential from cow manure:
Anaerobic Digestion to Produce Biogas
Anaerobic digestion involves the breakdown of organic material like manure by microorganisms in an oxygen-free environment. This produces biogas consisting mainly of methane and carbon dioxide.
The biogas can be used similarly to natural gas. Some applications include:
- Generating electricity using generators or microturbines
- Powering heating or cooling systems
- Fueling cooking stoves and equipment
“Anaerobic digestion of cow manure provides a clean burning fuel while reducing greenhouse gas emissions.”
Combustion for Heat and Power
Dried cow manure can be burned directly to produce heat and electricity. The process, known as combustion, involves burning the manure in the presence of oxygen to generate hot gases.
The heat from combustion can be used for:
- Heating water to produce steam to run turbines and generate electricity
- Providing heating for buildings or industrial processes
The ash residue from combustion may also be a useful fertilizer due to its nutrient content.
Thermochemical Conversion to Bio-oil and Syngas
Thermochemical conversion uses heat, pressure, and catalysts to convert dry cow manure into bio-oil and syngas in a reactor.
- Bio-oil can replace heating oil or diesel as a liquid fuel
- Syngas is a mixture of hydrogen, carbon monoxide, and methane that can be used similarly to natural gas
These end products are more energy dense and easier to handle than raw manure.
Pyrolysis to Produce Biochar
Pyrolysis involves heating cow manure in the absence of oxygen to produce biochar. Biochar is a charcoal-like material that has several uses:
- Can be burned for energy
- Can be used as a soil amendment
- Can be converted to syngas through additional thermochemical processes
Key Factors for Successful Manure-to-Energy Systems
Here are some important considerations when setting up an energy recovery system using cow manure:
Adequate manure supply – A minimum amount of daily manure production should be available to justify the capital costs. Larger dairy farms over 200 cows are ideal.
Proper storage – Manure storage tanks must collect and contain the manure to prevent environmental issues. Tanks should be covered to capture biogas.
Effective pre-treatment – Removal of contaminants like sand and grit minimizes wear on downstream equipment. Solids separation may also be required.
Careful process control – Factors like temperature, pH, and organic loading rate must be monitored and controlled to maintain optimal conditions.
Experienced operations and maintenance staff – Trained personnel are required for smooth operations and to carry out maintenance procedures.
Access to equipment suppliers – Proximity to manufacturers facilitates acquiring replacement parts and servicing.
Offtake agreements – Having contracts to sell the energy generated provides secure revenue streams. This improves project economics.
Case Study: Loyalist Energy’s Anaerobic Digestion Plant
Loyalist Energy operates an anaerobic digestion facility alongside a dairy farm in Ontario, Canada. This facility provides a real-world example of harnessing energy from cow manure.
Input feedstock includes manure from 650 cows producing over 6 million gallons per year.
Two covered lagoons capture biogas which powers a generator to produce up to 1 MW of electricity.
The electricity is exported to the local utility grid. This provides a new revenue stream for the dairy farm.
Digestate liquid from the process is recycled as fertilizer for crops. This reduces requirements for artificial fertilizers.
The project qualified for Ontario’s Feed-In Tariff program which provides long term contracted pricing for the generated electricity.
This case study demonstrates that cow manure can be successfully leveraged to create energy and new revenue channels while supporting sustainable agriculture.
Converting cow manure into energy is an effective strategy to extract value from an otherwise wasted byproduct. Technologies like anaerobic digestion and thermochemical conversion provide pathways to produce renewable fuels and power. Implementing manure-to-energy systems requires careful planning and investment but can provide environmental and economic payoffs. Unlocking the energy potential in cow manure presents new opportunities for dairy farms and rural communities to enhance sustainability.