How to Turn Manure Into Methane Gas with a Homemade Biodigester

How to Turn Manure Into Methane Gas with a Homemade Biodigester

Introduction

Converting manure into methane gas, also known as biogas, with a homemade biodigester is a great way to produce renewable energy and deal with waste on a small scale.

A biodigester is an anaerobic system that uses microorganisms to break down organic material like manure and produce methane gas as a byproduct. The gas can then be captured and used as an environmentally friendly energy source.

Building your own biodigester is a fairly straightforward DIY project that can have many benefits:

  • It provides a free source of renewable biogas for cooking, heating, or generating electricity
  • It reduces odors and pathogens from manure
  • The liquid effluent makes an excellent organic fertilizer
  • It decreases greenhouse gas emissions from manure storage

In this comprehensive guide, I’ll explain everything you need to know to successfully turn manure into methane gas using a homemade biodigester.

What is Biogas?

Biogas is the mixture of gases produced by the breakdown of organic matter in the absence of oxygen. It is primarily composed of:

  • Methane (CH4) – 50-75% – The main component of natural gas that is combustible and can be used as fuel
  • Carbon dioxide (CO2) – 25-50%
  • Trace amounts of other gases like hydrogen sulfide (H2S), ammonia (NH3), and hydrogen (H2)

Biogas can be produced from raw materials like manure, food waste, plant material, sewage, green waste, and more. Anaerobic digestion is the process by which organic matter is broken down to produce biogas.

The methane content of biogas makes it a clean burning fuel source. When biogas is burned, the methane is converted to carbon dioxide and water. This makes it a renewable and low carbon alternative to fossil fuels.

Benefits of Producing Biogas

There are many advantages to installing a small scale biodigester to produce biogas:

  • It provides a free source of fuel for cooking, heating water, running small engines, or generating electricity
  • It reduces pollution from manure waste
  • The nutrient-rich effluent can fertilize crops and gardens
  • It decreases greenhouse gas emissions from manure compared to letting it decompose naturally
  • It reduces odors from stored manure
  • It kills pathogens like E. coli that can be present in manure
  • It diverts organic waste from landfills
  • It can offset purchased fuel costs

For small farms with livestock, a homemade biodigester is an excellent way to manage manure in a sustainable manner while benefiting from renewable biogas energy.

How Anaerobic Digestion Works

Anaerobic digestion is a natural process carried out by microorganisms that live in oxygen-free environments. There are four key stages:

  1. Hydrolysis – Complex organic matter like carbohydrates, fats, and proteins are broken down into simpler soluble molecules like sugars, fatty acids, and amino acids.

  2. Acidogenesis – The products of hydrolysis are further digested by acid-forming bacteria into simple organic acids, alcohols, hydrogen, and carbon dioxide.

  3. Acetogenesis – Simple molecules created through acidogenesis are further digested into acetic acid as well as carbon dioxide and hydrogen.

  4. Methanogenesis – The products of the previous stages are converted into methane gas, carbon dioxide, and water by methanogenic archaea bacteria.

This process happens spontaneously in wet, oxygen-free environments like swamps, wetlands, landfills, and in biodigesters. The conditions inside a biodigester favor anaerobic digestion so microorganisms can efficiently break down organic material and produce methane.

Choosing a Biodigester Design

There are several different biodigester designs to choose from when building your own system:

Floating Drum Digester

This type consists of a large plastic or concrete tank with an inverted drum floating on top that collects the biogas. As gas is produced, the drum rises. It’s a simple, low-cost design.

Fixed Dome Digester

A fixed dome digester is built underground out of concrete or plastic and has an immoveable gas storage dome. The gas pressure has to build up sufficiently before gas can be extracted.

Plug Flow Digester

With this design, organic material moves slowly through a horizontal tank, usually made of concrete. It has a relatively long solids retention time.

Continuous or Complete Mix Digester

A complete mix digester contains an agitator or pump to constantly circulate the contents. It works well with a thin, liquid feedstock.

For a homemade system using manure, a floating drum digester is often the simplest and most affordable choice. This design is easy to construct from locally available materials.

Biodigester Components

A basic floating drum biogas digester requires the following components:

  • Digester tank – A large sealed container where the anaerobic digestion takes place. This can be made from plastic, concrete, fiberglass, etc.

  • Inlet pipe – To feed manure slurry into the digester.

  • Outlet pipe – To remove the effluent liquid after digestion.

  • Gas pipe – To transport biogas from the drum to the point of use.

  • Floating drum – Gas-tight drum that rises and falls to store the biogas. Can be made from plastic or steel.

  • Manure mix tank – Mixes manure with water for optimum consistency before feeding to digester.

  • Gas appliances – Stove, lamp, generator, etc. to use the produced biogas as fuel.

Optional components like an agitator, heating system, overflow tank, and more can help maximize gas production.

How to Build a Homemade Biodigester

Follow these steps to build your own floating drum biogas digester:

Choose a Location

Pick a dry, level site near the livestock pen where fresh manure is readily available. Ensure adequate space for the size of the system. Dig a pit to construct the tank if needed.

Size the Digester Tank

Size the tank based on the amount of manure produced and desired biogas output. For example, a tank holding 250 gallons can process 25-30 gallons of manure daily and produce enough biogas for 2-3 hours of cooking fuel. Common shapes are cylindrical and rectangular.

Build the Digester Tank

Use locally available materials like plastic, fiberglass, concrete etc. Make sure the tank is airtight and the material will not corrode. Install the inlet and outlet pipes, with the inlet slightly higher. Add an access port with an airtight lid.

Make the Floating Drum

Fabricate a drum that floats on the digester contents from plastic, metal or fiberglass. Attach a guide so it moves up and down smoothly as gas is produced and stored. Seal the drum airtight with gaskets and connect the gas pipe.

Add the Mixing Tank

Install a tank with agitator before the inlet to mix manure with water to a pumpable consistency before entering the digester. The ideal ratio is 1:1 manure to water.

Insulate the Digester (Optional)

In colder climates, add insulation like straw bales around the digester to help maintain the temperature for optimum microbial activity.

Make a Storage Tank (Optional)

An additional underground tank can store excess biogas. Connect it to the floating drum with a pipe and valve.

Start Digestion

Load manure and water into the mixing tank, allowing it to enter the digester through the inlet pipe. Maintain temperature and loading rate for efficient digestion. Monitor biogas production!

Maintaining Your Biodigester

To keep your homemade biogas digester operating efficiently:

  • Load the digester daily with fresh manure slurry
  • Remove effluent regularly from the outlet
  • Check for leaks and fix any issues with seals or pipes
  • Monitor temperature and gas production
  • Clean out solid buildup annually via the access port
  • Avoid overloading the digester with excess manure
  • Maintain neutral pH inside the digester
  • Keep the digester area clean and protected

Regular maintenance will ensure optimal biogas production.

Using the Biogas

The methane produced can be burned directly for various purposes:

  • Biogas stove – For cooking or heating water. Provides a smokeless cooking fuel.

  • Biogas lamp – Gives bright light suitable for indoor lighting.

  • Electric generator – Generates electricity. Requires gas cleaning.

  • Boiler – Burns biogas for central heating or to heat greenhouses.

Make sure all biogas appliances have the proper piping, valves, and safety controls. The biogas can supplement or offset other fuel usage.

Safety Tips

Follow these precautions when installing and using a small scale biodigester:

  • Ensure all gas connections are airtight and properly sealed
  • Check for leaks regularly with soapy water
  • Place the biodigester away from dwellings in case of gas leaks
  • Avoid open flames near the digester and gas storage
  • Wear gloves and goggles when handling manure
  • Clean out blockages carefully
  • Shut off gas valves when not in use
  • Post warning signs about the flammable biogas

Being cautious when handling biogas and manure will keep your DIY biodigester running safely.

Conclusion

Constructing your own biogas digester is a worthwhile project for generating renewable energy from manure. If done properly, it can produce sufficient methane gas to help meet cooking, lighting, heating, or electrical needs while also managing manure waste. Be sure to size the system appropriately and follow safety precautions. With some DIY skills and initiative, anyone can build a functional biodigester from locally sourced materials. Experimenting with biogas production can lead to energy self-sufficiency!