Biogas Digester Design

There has been a lot of talk lately about cow flagellants that contain CO2 & Methane gas disrupting the atmosphere. But natural gases can be used as sustainable energy by simply Composting and harvesting the gas called Biodigesting which can be done at home. It has been used for 100 years in Wastewater Treatment. How to make a Biogas Digester.

Using an airtight reactor like a 55-gal drum
Add organic material, Dog Poop, garbage, or grass
Micro-organisms (bacteria) break it down in an oxygen-free anaerobic environment
Gas is produced
Renewable energy called Biogas is methane & carbon dioxide is burned as fuel
Solids left are used as fertilizer.

A self-sustaining existence will be the future for everyone who shares the earth as resources grow smaller and the population grows bigger, people need to think out of the box and leave less of a carbon footprint than the generation before. Some of these new approaches have been used for quite a while in fact thousands of years.



What is Anaerobic Digestion


Anaerobic Digestion is a collection of a natural process that uses microbes to break down biodegradable organic material such as animal or food waste in the absence of oxygen. The process has been around for decades and was developed for Farms and Wastewater treatment facilities. This biological process generates gas. This gas is sometimes called Biogas mostly made up of Methane and Carbon Dioxide.


Anaerobic Digestion happens in 3 steps:

  1. Decomposition of plant or animal matter by bacteria into molecules such as sugar;
  2. Conversion of decomposed matter to organic acids;
  3. Organic acid conversion to methane gas.


The Anaerobic process can occur naturally or in a controlled environment. In controlled environments, organic materials such as biosolids and other relatively wet organic materials, along with various types of bacteria, are put in an airtight container called a digester where the process occurs. Depending on the waste feedstock and the system design, biogas is typically 55 to 75 percent pure methane.

Anaerobic Digestion is used as a process in Sanitary Sewage Treatment Plants to break down organic material in sludge that is generated at Sewage treatment plants. If you ever passed by a Wastewater Treatment Plant, you may have seen or smelled a Sludge Digester that is sometimes made up of 2 floating-top tanks where the byproduct of Sewage treatment which is sludge is further treated and converted to a more stable material.

After the sludge is decomposed or digested, The sludge is dewatered by settling then, taken out of the Digester dried, and dewatered again in a greenhouse. The stabilized sludge is finally rendered safe and used in farming and agriculture. The use of Anaerobic Digestion dates back to the early 1900s. More and more cities across the country are concentrating on sludge removal because of the high cost involved with handling it.

What is a Biogas/AD plant? and How does it work?



How Does Anaerobic Digestion Work

Two Digester systems for Sewage Plants are normally used with one being heated and mixed so that bacteria can have contact and breakdown the volatile organic material then the Biosolids are transferred over to the second Digester in order to settle out and separate the solids from water which is sent back to the head of the plant to be treated further.

As the sludge is broken down gasses are released like Methane that is used to heat the primary tanks by a Heat Exchanger. Digesters are designed to run at different target temperature ranges.

The temperature ranges are typically 86 – 100○ F for mesophilic and 122 – 140○ F for thermophilic. There are different populations of anaerobic microbes that thrive in these temperature zones.

In Anaerobic Digestion bacteria are kept in a certain high temperatures range. This is needed for bacteria to perform and function. The leftover Methane can be used to generate electricity and run the facility or burned off into the atmosphere.

Co-digestion occurs when anaerobic digestion is used to break down multiple types of organic waste in one anaerobic digester. Organic wastes that can be used in co-digestion with manure include restaurant or cafeteria food wastes; food processing wastes or byproducts; fats, oil, and grease from restaurant grease traps; energy crops; and crop residues. Co-digestion can increase biogas production from low-yielding or difficult-to-digest organic waste


Wastewater Reuse

How to Make Biogas

An Anaerobic Biodigester simply means a tank that digests organic material biologically. It works along the same lines as an Anaerobic Digester used on Farms and in Wastewater Treatment plants.

A Biodigester uses bacteria to break down organic matter just as an animal or person does and capture methane released by the bacteria in a process called anaerobic fermentation. Anaerobic means the micro-organisms digest the food in the absence of oxygen.

There are several kinds of microbes at work. Some break the food into simpler molecules of sugars and acids. Other microbes, which find oxygen toxic, are able to break down the simple organic matter to form gases, including the burnable gas methane or what’s called Biogas.

Methane, the main chemical in natural gas, is trapped and can then be burned for heating and electricity. The leftover organic solid waste can be used as fertilizer, a soil supplement, or further composted. The main resource is Biogas which can is used as energy to run the self-sustaining operation besides producing high nutrient fertilizers at a surplus.

Smaller units for your backyard work with your garbage the same as the huge Digesters for Sewage Treatment Plants work with sludge. Farms that create Biogas with manure from their farm animals also use the same bacteria that run through the three steps of Anaerobic Digestion.


Animation of “The Solar CITIES mini Biogas Digester”



When people eat food, food passes through their digestive system. The food material that the body does not use is expelled from the body in the form of urine, feces, and gas. A critical part of digestion in humans animals and nature is done by microbes.

Some of the microbes in digestive systems and in nature produce a gas, methane, as a waste product. That Biogas is now being utilized for a self-sustaining process that when refined and controlled uses no energy and can be harvested for a surplus.

Anaerobic Digestion can offer Biogas a new energy resource that means an opportunity for waste reduction and at the same time prevents Methane & CO2 from getting into the atmosphere.


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JimGalloway Author/Editor








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