How to Build a Manure-Powered Methane Digester


Building a manure-powered methane digester can provide numerous benefits for a farm, homestead, or small community. Methane digesters allow you to convert manure and other organic wastes into usable biogas for heat and electricity generation. I built my own small-scale methane digester to generate biogas on my homestead, and it has been an invaluable asset. In this article, I will walk you through the entire process of constructing and operating a basic methane digester system from start to finish.

Selecting a Digester Design

The first step is deciding what type of digester design you want to build. There are three main types of digesters:

Continuous Flow Digesters

These are the simplest and most common designs. Manure and waste are constantly added to the digester, displacing earlier material. Continuous flow digesters provide a steady supply of biogas. However, they require daily maintenance.

Batch Digesters

In a batch digester, new material is only added after the previous batch has fully processed. This results in periodic biogas production. Batch digesters require less daily maintenance but more effort when loading new batches.

Plug Flow Digesters

Plug flow digesters function similar to batch digesters, except new material is added to one end of the digester as processed material flows out the other end. This provides semi-continuous biogas production with less maintenance than continuous flow.

For small home-scale digesters, continuous flow designs tend to be the most practical option. Larger community or farm-scale digesters often utilize plug flow instead.

Sizing Your Digester

Properly sizing your digester is crucial. Undersizing will limit biogas output, while oversizing increases costs. Follow these steps to calculate digester size:

Size digesters conservatively to account for expansions or fluctuations in manure supply.

Choosing a Digester Vessel

The digester vessel holds the manure slurry during digestion. This vessel must be:

On my homestead, I used a 1000 gallon polyethylene tank designed for water storage. However, other options include:

Digester Heating Systems

Methane digesters operate best between 90-100°F. Some form of heating is required to maintain these temperatures for optimum biogas production, especially in cooler climates. Heating options include:

I installed two 4x8 foot solar thermal panels on my digester to provide heating using free solar energy.

Mixing the Digester Contents

Frequently mixing the slurry allows better contact between the bacteria and organic material. This improves biogas yields. Mixing methods include:

I mounted a mixing paddle connected to a small 1/8th horsepower motor to automatically churn my small digester's contents for 5 minutes hourly.

Plumbing the Digester

Proper plumbing allows loading and offloading the digester, recycling mixing liquid, capturing biogas, and heating. Key plumbing components include:

Use piping sized for adequate flows and resistant to corrosion and heat. I used 2 inch PVC piping for my small digester's plumbing.

Monitoring Your Digester

Monitoring some key parameters allows optimizing your digester's performance:

I monitor temperature and biogas daily and pH weekly. This gives me excellent insight into my digester's health.

Using the Biogas

The biogas produced by digesters is mostly methane along with carbon dioxide and trace gases. Methane is the valuable fuel gas. Biogas has many useful applications:

I run my biogas through a basic biogas burner to help heat my workshop and affiliated buildings. During warmer months, I use the surplus gas to operate a small biogas generator for electricity.


Constructing and operating a compact manure-powered methane digester provides numerous benefits. Digesters allow producing renewable biogas fuel from waste products and require fairly minimal maintenance. This article has provided an overview of key considerations, components, and steps involved in successfully building a functional digester system scaled to home or small farm use. With adequate planning and preparation, anyone can build their own digester to enjoy the benefits of waste-to-energy.