What Is Anaerobic Digestion?

What Is Anaerobic Digestion?

Anaerobic digestion (AD) is a microbiological process that uses anaerobic conditions to convert organic waste into biogas and digestate. Without oxygen, it’s a sequence of processes involving microorganisms that break down plant and animal matter. The anaerobic digestion process happens in an anaerobic digester — a sealed, oxygen-free tank. Organic materials such as slurries, food waste and crop residues convert into biogas, a methane-rich gas used as a digestate, renewable fuel, fertilizer and more.

Anaerobic digestion is a cost-effective, environmentally friendly solution for dealing with waste. Instead of sending it to a landfill — which can damage wildlife habitats and lead to dangerous methane emissions — or burning it — which subjects individuals and companies to strict regulations and burn standards — anaerobic digester cleaning plants turn waste into something potentially useful.

Let’s take a deeper look into how the anaerobic digestion process works, what the benefits are, how often a digester tank should be cleaned and more.

How Does The Anaerobic Digestion Process Work?

Anaerobic digestion is the process of anaerobic digestion in the digester. It’s the natural biological decomposition of organic materials — plants and animals — by microorganisms devoid of oxygen.

Anaerobic digestion for the purpose of biogas creation happens in a sealed tank known as a reactor. In these reactors, the waste material is digested by a complex of microbial organisms, producing biogas. It is then expelled from the digester. You can combine several organic materials in a digester in a process known as co-digestion.

Take a look at the following materials that can process in a digester:

  • Industrial organic residuals
  • Wastewater biosolids
  • Food scraps
  • Animal manures
  • Municipal wastewater solids
  • Fats, oils and grease (FOG)

Benefits of Anaerobic Digestion

Anaerobic digestion is deemed more sustainable than composing digestion. These digesters provide an array of benefits compared to traditional systems, including:

  • Sustainable production: Anaerobic digestion allows for sustainable food production, energy production and can even produce more sustainable fertilizers.
  • Waste removal or conversion: This process converts waste into green energy. It can also be purified to become biomethane.
  • Improved processes: The anaerobic digestion process reduces odor below unprocessed levels compared to other methods.

Benefits of Anaerobic Digestion

What Is Made During the Anaerobic Digester Process?

Anaerobic digestors produce either biogas or digestate. Natural bacteria that dwell within oxygen-free anaerobic digesters kickstart the process. These organisms break down organic substances as they develop. Biogas is produced as organic matter decomposes.


Biogas is a renewable fuel that is composed of mostly methane, carbon dioxide, hydrogen sulfide, water vapor and other substances. Carbon dioxide and other gases can be eliminated during this process, leaving only methane, which is the essential component of natural gas.

The energy produced in biogas can help organizations:

  • Generate or deliver heat and electricity.
  • Produce mechanical power.
  • Supply businesses and homes.
  • Run vehicles with alternative fuel.
  • Use renewable natural gas.
  • Provide power cooling systems.


The excess substance left over from the digestive process is known as digestate. The nutrient-rich, wet substance is separated into solid and liquid parts and can be utilized for a variety of purposes, including:

  • Creating sustainable nutrient-rich, organic fertilizer.
  • Animal bedding.
  • Crop irrigation for small and industrial farms.
  • Creating organic compost.

Anaerobic Digester Cleaning Designs

Once the organic materials are prepared and ready, it's then added to the anaerobic digester. Given the collection system type, the digester provides ideal conditions for converting waste into biogas. There are many different types of anaerobic digesters available.

For organic waste like manure and industrial wastewater treatment, anaerobic system designs include:

  • Covered lagoon digester: A covered lagoon design includes a flexible cover and a sealed top where methane is collected and supplied to the combustion device. For integrated digestion and storage, some designs use a single cell.
  • Plug flow digester: This type of digester uses a narrow concrete tank with a flexible or firm cover. It’s primarily used at dairy farms and collects manure by scraping.
  • Complete mix digester: This digester is designed with a heated tank enclosed with a mechanical, hydraulic or gas mixing system. These complete mix digesters perform optimally when the excreted manure is diluted with water.
  • Dry digester: The dry digester is a silo-style digester made of concrete and steel with a firm cover. These operate with dilute liquid matter or co-substrates and dry matter, like manure and crop residuals.

Bristol’s Anaerobic Digester Cleaning Solution With Zero-Human Entry

Cleaning your covered lagoon or tank on a regular basis is critical to its structural integrity. Traditional digester tank cleaning methods can often be challenging and expensive. That’s why Bristola’s proprietary Submersive Robotic Cleaning Systems solves these timely issues by using a submersible, remotely operated vehicle (ROV) to reach the sediment.

The system is an anaerobic digester tank cleaning service system that cleans and maintains your tank, covered lagoon and similar, ensuring it remains in good condition. It’s a zero-human entry system that allows our remotely operated vehicles to enter your covered lagoon or tank without removing the cover of the lagoon or lid of the tank. The system also stores data and reports information about your tank's condition.

Our ROV is attached to a hoist system and goes in from the roof of your tank or at the top of your lagoons cover to the floor at various heights. With our advanced systems in place, you can save money, enjoy more convenient processes and implement improved safety measures for employees.

A digester tank should be cleaned at least once every several years and as needed to ensure it’s running at its optimum efficiency.

Get Your Anaerobic Digester Cleaned with Bristola

Anaerobic digester cleaning is imperative, regardless of the type of digester used. Our zero-human entry cleaning system keeps your liquid storage facility working to its full potential — all while saving you time and money on maintenance and cleaning.

Bristola also offers a unique entry portal that can be placed on the manhole of tanks to allow us to easily re-enter and service your tank in the future.

As an industry-leading company with over 20 years of experience in the field, you’ll be provided with industry experts in anaerobic digester cleaning. Contact Bristola to learn more about our Submersive Robotic Cleaning System or request a demo today.

Get Your Anaerobic Digester Cleaned with Bristola