different types of anaerobic digester

a smoking landfill site: an industrial scale anaerobic digestion process without any controls. The gases all escape and the by products are not utilizedanaerobic digester out of control: in a smoking landfill site the gases all escape, causing global warming and the other by products like nutrients are not utilized

Free Picture: Garbage In Paradies ID: 138693 © Slidepix | Dreamstime Stock Photos

What is special about an anaerobic digester that sets it apart from large scale anaerobic composting as simple and wasteful as illustrated above. A digester contains the process, and in a digester the temperature, water content and other parameters are controlled for optimal processing and the container traps the escaping gases. 

The question remains as to what separates the various kinds of industrial anaerobic digester and what levels of sophistication can be reached in their design. I wish to delve into this question of the difference between various kinds of anaerobic digesters… with the understanding of an amateur of course, because it has become quite complex and it is interesting too, and empowering. If you know where your waste is going when you flush the loo or bring out your wheelie bin, you are so much better equipped to take the right public action on waste treatment.

different kinds of anaerobic digester by process, material, complexity, and duration 


The first two major types of processing are the batch versus continuous process mode. Batch processing is simpler, and basically is the processing of one batch of organic waste in a digester where it remains till digestion is completed. To accomplish the movement of material required for the continuous process mode, various types of flow are used such as stirring, or upflow anaerobic sludge blankets through which a constant stream of highly liquid waste water allows solubles like sugars to pass through the system quickly as they process quickly, but traps particles of sewage with gravity, for up to 90 days so that they can cure fully. These digesters produce a high methane harvest.


The second major difference between digestors according to Wikipedia, is in the broad physical characteristic of the material as solid or liquid. A multistage process involving stirring movement or pumping of any kind works works with more liquid media, whereas high solids media are stackable and suit batching, because stirring semi solid material requires a high energy investment. Dryer material, composted in tunnels, produces next to no waste water.


Another difference between digesters is their different levels of complexity. This the authors divide into one and two stage processing. One stage are batch systems, which are just one sealed container, or anaerobic lagoons which are a single open dam.  Two stage processes may allow the first three stages of anaerobic digestion, hydrolysis, acidogenesis and acetogenesis to occur in one container, for about 14 days, which is then heated and pumped to a second container for methanogenesis for a further 14 to 20 days.

For processing in which there is no stirring, the process can be batch or continuous. The continuous vertical plug flow digestor feeds in material from the top, which drops slowly down a cylinder, by gravity, the finer the material the faster the digestion and the sooner the digested material will exit. Batch tunnel digesters deposit material in a tunnel with airtight doors, but this broad type of digestor also can use aerobic decomposition, in which case coarse material is good as it allows aeration.

The wetter the substrate is, the more bacteria can come into contact with it, and the higher the gas production. The ideal C:N ration is 20-30:1. Excess N can produce too much ammonia and cause inhibition of methanogenesis.


Time in the digestor is another factor that is important in this industry. Note that within the digestor, the full anaerobic decomposition takes 4 – 5 weeks. Compare this to frequently stirred aerobic hot compost which takes 18 – 24 days. It is slower but in a digester but nothing like the year required for anaerobic composting at home. An upflow anaerobic sludge blanket system requires 90 days for full digestion of the slowest form of putrefaction.

Some by products of the digestive process, such as ammonia, and some nutrients normally found in plants (light metal ions like Mg, Ca ) and contaminants like aromatics and heavy metals, and some larger molecules such as long chain fatty acids may slow digestion down.

The chemical complexity of the digestor food dictates the it time to digest. The higher the digestibility of the material, the higher the gas yield from a system. The high yielding materials seem to be what we call ‘green’ material in the compost mix (food left overs, grass clippings, sewage, animal waste) except for paper which is also high yield. I’ve also found paper products to be very nutritious in the vermiculture situation as worm food. 

The low yielding materials are the woody waste part of plants, high in Lignin. Lignin and cellulose natural plant polymer combinations can take longer to break down. Lignin processing bacteria (Xylophageous anaerobes), or high temperature pretreatment in or outside an industrial digestor can break down this lignin.



home page for green inspirations


soil fertility and different kinds of composting


simple home based anaerobic composting


the chemical process of anaerobic digestion

Restore Nature Newsletter 

I've been writing for four years now and I would love to hear from you

Please let me know if you have any questions, comments or stories to share on gardening, permaculture, regenerative agriculture, food forests, natural gardening, do nothing gardening, observations about pests and diseases, foraging, dealing with and using weeds constructively, composting and going offgrid.

[ ? ]

Upload 1-4 Pictures or Graphics (optional)[ ? ]


Click here to upload more images (optional)

Author Information (optional)

To receive credit as the author, enter your information below.

(first or full name)

(e.g., City, State, Country)

Submit Your Contribution

  •  submission guidelines.

(You can preview and edit on the next page)


Our New Book  

DIY Grey Water Wetland

Build your own system and grow fruit and vegetables with your dish water and other waste water at home

Order the Kindle E-book for the SPECIAL PRICE of only


Prices valid till 30.09.2023

Recent Articles

  1. German snails

    Jun 21, 24 07:18 AM

    lovely video on german snail species their uses in the garden as indicators composters: https://www.youtube.com/watch?v=4byhHGvSFb0

    Read More

  2. Curious about your 'Hardy garden mushroom'

    May 30, 24 02:48 AM

    Your site was 1 of my top results while doing an image search through Google. The image I used was a fairly poor picture that I took of some mushrooms

    Read More

  3. Rose

    Dec 17, 23 04:08 AM

    I am doing research on growing wildlife foraging plants to use in enhancement plantings with wildlife in mind. My thoughts after seeing bears too skinny

    Read More

How to make

$ -MONEY - $

with earthworms

The Book 

"How to start a profitable worm business on a shoestring budget 

Order a printed copy from "Amazon"  at the SPECIAL PRICE of only


or a digital version from the "Kindle" store at the SPECIAL PRICE of only


Prices valid till 30.09.2023



How to make good Compost.


Worms Recycle Dog Poop