Here are the original diagrams that Chris, Vic, and Harley came up with when they wanted to build an agitation system for the prototype batch digesters at the UBC Energy Farm. This system is designed to mix the substrate and break-up the hard layer of scum that forms on top of the digestion slurry. To understand the process better, I allowed scum to form on top of a specific anaerobic bacteria culture I was observing. I noticed that bubbles do form but are trapped under the thin scum layer- like a small balloon. We don’t want this to occur during large scale production, and so we have made some modifications to the typical batch digester design.

Biogas Agitation Original Diagram

Bearing Orientation Diagram

Typical Small Scale Batch-Style Digester with 55 Gallon Oil Drum

The biogas research is moving along at the UBC Energy Farm. Today, Christoffer Hansen met with Vic and Harley from C.W. Brockley in Vancouver, B.C. to finalize design considerations and begin the construction of the agitation system for each prototype digester. These gentlemen are attempting to create a biogas digester that not only performs the necessary actions required to keep the bacteria happy and making biogas, but one that is able to be replicated using items that are cheap, easy to source, and easy to assemble. The design that they have come up with is unique because small-scale batch digesters do not usually have suitable agitation systems. The result of weak agitation is twofold. First, a hard layer of scum forms on the top of the mixture, disrupting the production of biogas. Second, the methane forming bacteria have a harder time making contact with the tiny bits of organic material that they use to make biogas.

The basic design of the agitator is a shaft that runs the width of the inside of a 55-gallon oil drum, about 6-8 inches from the top. There are pieces of flat bar attached to the shaft in various orientations which will break the scum and the surface of the substrate. Outside the 55 gallon drum the shaft is turned on a bearing by using a hand crank. This will be a safe and effective way to mix drum contents.

Julian Darley visted the farm today and delivered two temperature sensors from California based, Davis Instruments. These temperature probes will give researchers digital data related to the temperature of the digesters.

There are exciting new developments related to the current biogas research at the University of British Columbia Energy Farm. Recently, Christoffer Hansen delivered a report on the feasibility of producing year-round biogas at the UBC energy farm. After reviewing the report, both Julian Darley (Founder and Director of the Post Carbon Institute) and Mark Bomford (UBC Farm Manager) have agreed to move the research into the next stage. Two modular batch digesters will be built and housed in a glass greenhouse in order to demonstrate and troubleshoot biogas generation during the winter. The biogas will be derived from a mixture of clover, dry leaves, and a small amount of lama dung. To give researchers a virtual window into the digestion process, computerized sensors will be placed inside each generator to log temperatures and changes in Ph.