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Summer School Individual Project. Bio-Energy Summer School 2009 Taylor Norrell. Project Goal. Make an anaerobic digester that combines the gas storage unit and the digestion tank into one unit, using as little materials as possible. Anaerobic Digestion.

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Summer school individual project

Summer School Individual Project

Bio-Energy Summer School 2009

Taylor Norrell

Project goal
Project Goal

Make an anaerobic digester that combines the gas storage unit and the digestion tank into one unit, using as little materials as possible.

Anaerobic digestion
Anaerobic Digestion

Breakdown of complex organic materials into a methane/carbon dioxide “biogas” and a nutrient rich effluent

Biomass Magazine, February 2009,

Benefits of anaerobic digestion
Benefits of Anaerobic Digestion

  • Biogas can be used for heating and cooking applications

  • Effluent can be applied to crops as fertilizer

  • Anaerobic conditions are effective treatment for pathogen elimination

Digester design
Digester Design




  • Essential for proper digestion

  • Helps prevent slurry layering

  • Well mixed digester is a healthy digester

First attempt
First Attempt

  • Agitates by moving the gas collector up and down

  • It was found that it was hard to move the collector up and down

  • It was also found to be very messy, contents from the digester would overflow when the gas collector was being pushed

  • Structure required a lot of pieces and was not very simple to make

Second attempt
Second Attempt

  • Agitator consists of the top of the gas collector attached to 4 ropes which run through a series of pulleys. When the ropes are pulled, it lifts the top through the digester, stirring the contents. A brick was added so the top can sink to the bottom after being lifted.

  • Ropes became easily tangled

  • Without the right pulleys, it was difficult to pull the ropes.

Final attempt
Final Attempt

  • Took two 2”x4” and screwed them together to make an ‘L’ shape. Screwed on the top of the gas collector to the bottom.

  • Agitates by the user lifting it up and down.

  • This was the simplest to make and the most effective mixer.

Gas collector
Gas Collector

  • The inverted barrel acts as the gas collector

  • Methane is formed in the digester and rises up out of the slurry, and gets caught in the collector

  • On top of the collector, a PVC pipe with a ball valve acts as the gas outlet

Summer school individual project 1349872

  • The cage is the wooden structure surrounding the digester, attaching four ropes to the gas collector

  • Helps stabilize the collector and promotes gas production by creating a lower pressure environment in the digester

Summer school individual project 1349872

  • A layer of vegetable oil separates the slurry from the open air

  • This serves to keep conditions in the digester anaerobic

    • Acid forming bacteria are facultative anaerobes, methane forming bacteria are obligate anaerobes

  • Helps to manage odor and pests.

Problems solutions

  • As gas collector rises, it brings some contents out with it, attracting pests

  • Possible solution: incorporate some sort rubber lining/brush to wipe off the collector as it rises

  • As scum forms, it rises above the oil layer and can attract pests

  • Regular agitation should maintain any scum problems, otherwise the oil layer can be skimmed to remove scum