It has been a week since the initiation of the probiotic fertilizer and the batch-style biogas system at the Local Energy Farm Demonstration Project located at UBC. At present, certain aspects of daily farm upkeep rely on the work of dedicated volunteers. I considered this in the creation of the biogas digesters and attempted to make a system that was as easy to maintain as possible for the volunteer workforce.

At minimum, the biogas digesters need to be agitated once a day. In my perfect world, agitation would occur three times—once in the morning and twice during the heat of the day. Remember, agitation breaks up the hard layer of scum that tends to form on the surface of plant based substrates and it mixes the plant matter in order to allow bacteria to come into contact with new material to digest. Agitation should take about thirty seconds for each digester. A volunteer cycles the handle clockwise for about 5-10 revolutions and then counter clockwise for another 5-10 cranks. Simple!-Finished and on to the next farm task!

The probiotic fertilizer needs less frequent agitation (once a week instead of daily). The “airtight” lid is taken off the brew, a wooden oar is inserted into the mix, and the contents are mixed and churned for a minute or two. Usually this makes a lot of foam as carbon dioxide is released from the mixture. After mixing the lid is re-secured and awaits the next week.

As you consider the infrastructure and process you are going to develop on your farm try to make it use as less energy as possible for up keep and maintenance. To invest a little extra thought and energy in the planning and design phase can allow you to have multiple initiatives underway, which, once started, can continue without a lot of extra physical input.

I have been using a template presented by the United Nations Department of Food and Agriculture as a general guide for the creation of the biogas system at the Energy Farm at UBC. This booklet suggested using rubber tire inner tubes as the gas capture system, a suggestion that I eventually chose against at the Energy Farm.

The U.N.’s suggestion is that tire inner tubes are simple to repair, easy to acquire, and can suitably store biogas for later use. While I find this idea appealing in situations of scarcity and as a means of reusing rubber that might be simply thrown out, I feel that taking a little more time to build a drum style gasholder is better overall choice for this biogas system.

The basic design of the dome style gasholder is as follows:

1.Invert a drum so that the holes on the lid face toward the ground

2.Remove or cut off the top of the drum

3.Insert a PVC pipe into one of the holes in the lid so that it stands vertically inside the inverted drum

4.Fill the main drum with water to about 3 inches below the top of the pipe and place another drum inside (inverted so that can collect the gas)

This “floating dome” style of gas collection captures a large amount of gas that is distributed using only one outlet. Moreover, all biogas digesters can have their gas routed to this single gas collecting dome. As the gas collects under the drum, the water acts as a seal so no gas escapes. Weight is put on the top of the second drum in order to determine the pressure of the system when connected to a stove or appliance. As the drum is pushed closer to the water more pressure is created and gas flows out through the PVC pipe toward the appliance.

I inverted a 50 gallon plastic drum, cut the top off, filled it up with water and placed a 20 gallon plastic garbage can to form the gasholder. I liked the fact that I could use plastic in this part of the system because it ensures the long life of the gasholder. While the inside of digesters Ludwig and David had to be painted with a protective paint, the plastic drums need less preparation and are guaranteed not to corrode from the gas.

Gasholder of Prototype Biogas System

The biogas construction project has been completed! On Tuesday I was able to connect the digesters to the gasholder, buffer the substrate, and add the seed cultures.

I found that buffering the substrate required much less alkaline material than I expected to use. It took 40grams of baking soda to buffer the clover/leaf batch inside digester David, while digester Ludwig used 35grams. This was enough to change the acidic solution (pH 5) to a more basic solution between pH 7-8. I checked the pH with litmus paper multiple times during the day and the pH of the clover/leaf substrate remained a constant 7-8. Farm manager, Mark Bomford, noted that the leafs inside the substrate have an excellent buffering capacity and will be able to absorb a lot of the baking soda. So, while the substrate seemed adequately buffered at 7-8 on the day that I added the seed cultures, it might become more acidic after the leaves absorb the baking soda water. I am nervous about his suggestion as we are now left to monitor how the buffering plays out.

Four different anaerobic seed cultures were used to inoculate the digesters. I used a culture of lama and sheep manure, a culture of lama and clover manure, a mixture of sheep and clover, and a mix of only clover and leaves. These cultures were maintained under protection inside a glass greenhouse for over five weeks. During that time I had observed gas production on the surface of all cultures using the sheep and lama dung and felt that those cultures offered a large population of methane forming bacteria. However, the mixture of only leafs and clover did not seem as active and I did not expect it to be a suitable seed. As I added the seed cultures to the digesters I checked the pH of each one. As I expected, the cultures using lama dung were defiantly basic at a pH of 7-8. The leaf and clover mix was very acidic at pH 5.

The acidic clover leaf culture lends us insight into the necessity of brewing appropriate bacteria cultures for seeding. Anaerobic bacteria can and will grow inside plant only mixtures, however, even in optimal growth conditions, it might take months. That is why a source of dung is useful when creating live cultures in a shorter period of time. I think it is reasonable to suggest that the plant only seed was stuck in the acid forming phase, where bacteria are breaking down the plant material into fatty acids. Without a suitable amount of methane forming bacteria to gobble up those acids the process gets stuck and the solution remains acidic. Literature suggests that this process will correct itself eventually because the bacteria that form the fatty acids will begin to drown in their own toxins, slowing their reproduction and allowing methane forming bacteria to make headway against the overabundance of the acids.

After the seed cultures were added to the digesters I put the lids on and sealed them closed. I stuck plumbers putty under the lip of the lids so that I could assure a gas tight seal and then bolted the lids down. Agitation of the material was not hampered by the lid or the temperature sensors and the entire system seemed to be functioning as expected.

Prototype Biogas Digesters (David and Ludwig)

Gasholder for Digesters 

Today I was able to complete the probiotic compost tea I learned about while in Ecuador. The brew was made of clover, sawdust, yeast, molasses, humus (finished compost), rock phosphate, urine, garlic, and comfrey. I decided to throw the garlic and comfrey in to act as a natural insect repellent. This batch will be stirred once a week and will be stored next to the biogas digesters in the hoop-style greenhouse at the UBC Energy Farm. It should be ready in 45-90 days depending on winter temperatures-my guess is around a safe 75 days. The tea can be used as a foliar spray at a 1:10 ratio or as a soil improver at a 50/50 mix with water. I expect the batch to yield around 100 liters of concentrate. If you want the exact recipie email me at --> chrishansen@postcarbon.org .

The biogas project is near completion, and the lids are ready to be tightened down. I stuffed 19.5kg of mildly composted material into digester David and 10kg into Ludwig. Then I topped each digester off with water until there was about 10cm of space from the lip of the drum. The agitation system works fine but can be a little tough when digester David gets a pile of leaves pressed between the lid of the drum and the agitation arm. If I could make an improvement it would be to make the handles of the system a little bigger as to allow the user to get more torque and therefore make it a little easier to bring the arm around. However, perfection aside, the agitation system does not leak and works fine-I count that as a success.

I have some litmus papers that I have been using to check the pH of the water and substrate mixture. It is very acidic right now. On the color sheet between 4 and 5. That means that I have a long way to go to buffer the system to a pH of 7-8 to make the mixture hospitable for the methane forming bacteria that I plan to seed the digesters with tomorrow. My idea is that the substrate will seep into the water overnight and allow a substantial amount of acids to form. Then, tomorrow, I will use lime or baking soda to buffer the solution. I am leaning towards baking soda right now; however, there is plenty of lime at the farm.

For a little over a day, the feedstock materials have been undergoing aerobic decomposition in hopes of breaking down the plant matter before feeding the digesters. One of the digesters (a.k.a. David) will be fed a charge of 9Kg clover and 11Kg of dry maple leaves. Once David is filled with water the substrate will have a total solids concentration of about 11 %. The other digester (a.k.a. Ludwig) will be fed a mix of 4.5Kg of clover and 5.5Kg of dry maple and alder leaves. At about 6% solids this is a less dense concentration of material.

When these prototype batch-style digesters I decided to make two subtly different machines. Ludwig’s agitation system differs from David’s in one way—the depth of the agitation shaft. While David’s agitator is situated 6 inches below the top of the lid, Ludwig’s is positioned at 8 inches below the top. What this difference amounts to is as follows:

Ludwig’s system will be able to disrupt scum formation and will be able to mix the slurry from a deeper position. The intended idea was that the deeper agitation position would churn the substrate and allow the bacteria to come in contact with new bits of material to eat. In contrast, David’s agitation system is position higher on the drum. It too will be able to disrupt the scum formation and it has the advantage of allowing more material to be put into the digester. Given suitable conditions, more material is more biogas. Hence, I have decided on a smaller solids concentration in digester Ludwig because it might be too hard to turn the agitation handle through such a dense mixture. David, on the other hand, can handle the denser material and will break up the scum, allowing the digestion process to sort itself out below. In subsequent tests of the machines more material will be added to Ludwig to really get a test of what is the limit of the deeper agitation system as it attempts to churn dense plant matter.

We are moving forward with the biogas system at the Vancouver Energy Farm. The paint will be fully dry by tomorrow and we could technically start the digestion process. However, I will wait at couple of more days to let the clover and leaf feedstock undergo a little more aerobic decomposition. I picked up all the "plumbing" fittings at Vancouver Irrigation. These folks were quite helpful and allowed me to purchase the pipe-fittings at a wonderfully discounted rate--Thank You.

Potions of the pipe-fittings are intended to be a scrubbing chamber for hydrogen sulfide gas. Hydrogen sulfide smells like rotten eggs and is corrosive to the metal or brass in any system that you feed the gas to. However, the hydrogen sulfide gas can be scrubbed by corroding some other type of metal- in this case steel wool. The steel wool is placed inside an 18-inch long chamber. As gas pressure builds up in the digester the gas is forced through the steel wool on its way to the gasholder. Below are pictures that show the process of making the scrubbing system and how it is built into the digester lid.

Unrolled Steel Wool

Feeding Steel Wool Into Scrubbing Chamber

Biogas Digester with Scrubbing Chamber Extending from the Lid

I had to make an alteration in the feedstock. I was going to feed one digester clover-hay and dry alder leaves, aged 1+ years. But a majority of the alder leaves had too many wood chunks and other debris. Given the effort to pick through 10Kg of dry leaves to remove most of these items I decided that the alder leaves were unsuitable for this demonstration. So, I have reverted to using maple leaves and a mix of cleaner alder leaves to feed one of the digesters. It was not a major setback because maple leaves are abundant around the manicured UBC campus.

Today I hand-shredded 10Kg of dry maple leaves and I had time to ponder the carbon component of the feedstock. Although we need both carbon and nitrogen to make the bacteria happy while they consume the plant matter and respirate the biogas-it is really the carbon that is the methane forming aspect of the substrate. I was amazed at how much carbon is in 10Kg of dry leaves. While the weight of clover to carbon is almost equal in proportion, there seems to be a lot more leaves taking up space in the digester than clover.

The plan is to load the prototype batch digesters later this week. Each batch, (aka. charge), will be a mixture of chopped clover-hay, dry leaves, and a small portion of fresh lama or sheep dung. To prepare, I have processed all the clover and laid it out to rot. The dry leaves were collected about two-weeks ago. I want to mix the dry leaves with the clover at the proper proportions in order to create a carbon-nitrogen ratio of 25-30:1. By my estimates this will be roughly 10kg dry leaves (40:1) and 10kg chopped clover-hay (15:1).

After letting the clover rot overnight and part of Tuesday, I will mix in the dry leaves. This will entice aerobic mesophilic and thermophilic bacteria to break down the leaves and the clover. On Thursday or Friday I plan to add each composting “charge” into each digester and add water until about 4in/10cm from the top of the drum.

Since the aerobic bacteria will be decomposing the plant matter inside the biogas digester, the substrate will become acidic. Therefore, I need to “buffer” the charge by adding lime to the water. This should stabilize the pH of the substrate and set up a friendly environment for the methane forming bacteria that prefer a pH of about 7-8.

When the pH is in the healthy range I will finalize the process by adding the bacterial cultures that have been growing inside the greenhouse since the 14th of September. The cultures include mixes of lama dung and clover, pure sheep and lama dung, pig dung and leaves, and clover and leaves.

Anareobic "Seed" Cultures Inside Greenhouse Since September 14th

On Saturday I finished collecting my quota of 42 KG of what I can best describe as “clover-hay”. When I talk of clover-hay I am referring to the leafy tops of the clover with sections of attached stem. Pure clover tops are estimated to have a carbon to nitrogen ratio of 12:1 (pretty low). The clover-hay is estimated to be close to 15:1.

On the UBC Energy Farm we are certain that the collection and preparation of the clover for use in organic fertilizer and biogas digestion can be done without the use of petrol. It has now become a matter of finding the best means of doing this. In search of an appropriate methodology, researchers are interested in making the process easy to replicate, safe, and not impossibly labor intensive. As farm manager Mark Bomford puts it, “The goal is to find intermediate tools and methods that work at reducing a farmer’s dependence on petrol powered machines. At the same time, we also want to find ways of conserving needless physical labor and energy inputs.” So what are the intermediate tools?

I have used a push-style, human-powered, lawn mower. It cuts perfect clover tops without stems if the clover is about 5 inches tall. However, when the clover is very tall and dense the process becomes very time consuming and labor intensive, (because the mower is difficult to push). Furthermore, the quality of clover obtained is not as “pure” as only clover tops. I then tried to use a machete to cut tall dense clover and obtain clover-hay. This worked better than the mower but the process required that an individual bend over or kneel, putting strain on the legs and back. What’s more is that the clover-hay yield is low for the amount of time invested. Finally, I took a scythe to the same dense clover. BINGO! The scythe is able to cut large swaths of clover while standing in a comfortable way. When I am careful I can even go for only clover tops. I can level ten or more times as much clover in a fraction of the time.

The scythe is an example of an intermediate tool on the Energy Farm. It has a quick learning curve, is safe to use for an individual in an open field, and saves time and energy to obtain the same quality of cut clover. Further uses of the pole scythe at the Energy Farm include harvesting Flax and Canola for use in making biodiesel.

Feshly Cut Clover Hay

Mighty Scythe

Using the Scythe to Cut Clover (Dramatic Swing!)

 
Difficulty of Using Push Mower in Tall Clover

At the Energy Farm we are experimenting to find useful intermediate technology that maximizes the amount of work done while involving little to no petroleum input. Since many processes that are assumed in today's system of agricultural practice rely on machines, we are looking for ways around these assumptions in order to adapt to an energy constrained future.

Today I worked on discovering the methodology for collecting and processing materials to be used in the biogas digester and organic fertilizer that I am experimenting with. My aim was to harvest and process clover, (a nitrogen rich legume), without using petroleum powered machines like a gas mower or chipper/shredder. I was excited to try the new human-powered push lawn mower that has been purchased for the for the energy farm. As might be expected the mower easily cut the leafy tops off the clover. The clover was then collected using a fine-toothed grass rake. However, when it came to chopping clover that was much more over-grown a machete was used to complete the job. After I cut a full wheelbarrow of clover (about 11KG) I took the fresh greens over to be processed.

Regardless of whether we are making compost or collecting biogas digester materials we have to chop the ingredients into smaller pieces in order for the bacteria to break the plant matter down further into more simple molecules. Again the aim is no petrol, so I decided to grab handfuls of clover from the wheelbarrow, roll the handfuls into logs and chop it with a cleaver. This creates bits of plant that should mix nicely with the dry leaves that we intend to feed the biogas digesters.

Unprocessed Clover For Biogas Digesters and Fertilizer

Harvesting Clover with Machete

Chopping Clover with a Cleaver

The whole process of collection and processing took me around an hour. Although the push lawn mower and the cleaver seemed to work nicely for cutting and shredding, using the machete seemed a little awkward. Since there was so much bending over and sweeping arm motions I don't think I have found the right way to collect overgrown clover. I think I might try to collect materials later using a different tool.