Tuesday, April 28, 2020

Aerated Compost: Pallet Floor for Air Pipes

I'm excited to introduce something new to my blog: a guest post! Recently Ty and Sally Carlson posted an excellent, detailed comment on one of my previous aerated compost posts, sharing their experiences with the O2 system. They have built a pallet "floor" cleverly designed to improve aeration, and have generously allowed me to publish their comments on it here so that others can benefit. Most of this post was written by them, with my comments in italics.

Here is their comment on my previous post

Thank you for this post. We recently bought a small horse farm and my wife heard about O2Compost from Liberty Bell stables. I grew up on a dairy farm - it's critical to have a manure plan. I liked the idea of composting, read up on the material and my wife & I agreed. We decided to build 2 bins (we have 3 horses, planning on a 4th). A local handyman built two 4d x 6w x 4h bins and built simple low-cost flap-door-type lids with 1x4s & tarps.

I was an observer up to this part of the process as I was busy with my day job and moving from one house to the farm. We encountered a couple of start-up issues. My wife mis-remembered the settings for the blower (on for 30s every 30m). She initially set it for 30s every 30s and we succeeded in melting the impeller of the blower (replacement impeller is $12.84), plus you must scrape the melted remnants off the inside of the blower. Second is that you don't start the aeration until the bin is full. It wasn't a showstopper, but I sat down and actually read through the short manual cover-cover (which is pretty good and detailed).

We had the same observations as above - we can fill a bin in about 3 weeks, depending if we pick the manure in the pasture. We use fine pine bedding, we're not tossing in a lot of bedding material unnecessarily. The pile does compress once the bin is about half-way full, we can get close to month depending on when we pick the pasture. The challenge with two bins is that we need to start the aeration of the bin and the 30 day clock while we start filling the second bin.

We had tossed yard clippings into the bin as well, and with than and a pasture pick, we almost immediately got to half-full on bin 2 in a week (ack)! We weren't going to make that month - and bin 1 would not have completed active composting stage.

I built a third bin. Our handyman started, but I wanted the bins to be identical, and this third one was a bit shorter than the others. I dug down deeper to allow the bins to be the same size/height and completed the third bin just in time as the second one filled up. Our mistake early on was adding the grass clippings and other material before understanding the volume produced by the 3 horses.
A month later, the temps in bin 1 were down to 80F-100F, we had mushrooms growing on top and now bin 3 was nearly full. One useful note is that I took the "topping" layer off the finished bin (bin 1) and put it on the now-full bin 3. We unloaded bin 1. As noted in the original post, it's "cooked" but still in very recognizable forms. It has a musty, woodsy (but not unpleasant) smell. As it was mostly horse manure with some hay and bedding (fine pine sawdust) - it was relatively easy to unload.

The aeration pipes were a bit of a pain to work around. I'm trying something in bin 1 now that's based on the other (more commercial) systems. I've built what are basically 4" mini-pallets for the base of the bins (with the main supports perpendicular to the pipes to allow air flow under the load in the bin). The ground there is a bit muddy, so I think I will have a good seal around the edges of the bin (air won't escape under it), but I'm seeing if I get better/faster composting with more of the bin material exposed to airflow. It also addresses the note above as I have it built such that I use two 1x4 boards, one each covering the two PVC pipes in the bin - so I have a nice, level surface to remove the material. I lose a bit of bin capacity, but I'm seeing if that make the overall process a bit faster - both composting as well as removal. Finally, I'm incorporating a better lid-system - like the one above. In order to provide a buffer for the fourth horse, and more time in the bins in the 'curing' phase, I'm just completing a fourth bin. I have three blowers and am using the Valterra 4" gate valves to control routing of the airflow. As we clear the bins with existing compost, I will upgrade them w/ the 'pallet' floor and the improved lid-system.

Ty and Sally generously followed that up with an email that included photos of the ingenious pallet floor they have built for their bins. I'm quite jealous because working around my aeration pipes is the worst part of emptying the bins. The email and photos are copied below:

Greetings Libby,

I was actually going to recycle old pallets, but when I went looking, there were none to be found.  Now that I have purchased the wood, the co-op now has at least 20 free pallets stacked up <sigh>.

Oh well, these are treated boards, perhaps they will last longer.

The pallets themselves are just 2x4s and 1x4s, the overall interior dimension of the micro-bin is 43” x 72”. This is looking at the underside of the pallets, but you can see where the perforated pipes slot in, and the top section has an extra crossbeam which is where the perforated pipe stops – it adds a bit more support for the loose 1x4 that covers it.


This is a close-up of the left pallet section and the center pallet section before I installed them in the bin. I’ve added essentially lightening holes to make sure that air flows freely under the pallets and is not blocked by the extra crossbeams.  I put 3 x 1.5” holes in each of the pallet sections.


Here’s a close-up of the right pallet section.


Here are the pallets and the micro-bin.  The perforated pipes are 24” long. The pipes terminate 10” from the back of bin, that where the extra crossbeam is set (just shy of 10”). I use the Valterra 4” gate valves ($48.69 each (new) on Ebay). I want around the inside of the bin and placed muddy dirt along the bottom where it meets the ground to help create an air seal, so air doesn’t just pour out of a gap between the bin and the ground. I’ll do the same with the exterior to make sure there is a seal. Creating this lower plenum area does run the risk of the air just pouring out a gap in the structure.


Below is shown with the left and right pallets set in place. I cut the measurements by ¼” for the width of each section so there is room to place and remove them. The first section I did on the first bin I did I had a very snug fit – fine carpentry, but highly impractical. These are plenty snug, but are easy to remove.  You can see where the extra crossbeam sits – just at the end of the perforated pipes – provides support for the floating 1x4s which cover the pipes.


Now all pallets in…  You can see the crossbeams nearly/gently touching.  The pipes are held nicely in place as well, perforations are facing downward in the 5- and 7-O’Clock positions.


And with the floating boards in place. The boards fit nicely, have fairly consistent spacing, and all of the screwheads etc. are slightly recessed so shovels or loaders won’t get hung up on raised screwheads.  The front of the bin are 8 2x6s and one 2x9 at the top (in the front) to create a pitched roof for the water to run off the back.  I’m building the roof sections probably tomorrow – I like what you did with the supports and the line to open the doors. I’m planning on doing something similar.


I'm super impressed with this concept, and how lovely the Carlson's bins are. They have just started filling their first pallet-floor bin, and I am curious to hear in a few months how the floor affects the quality of the compost. Ty and Sally, please keep us updated!

You can read more about my experiences with the aerated compost system here:

Bin Construction
The Composting Process
Spreading
Is It Right For You?
3-Years of Composting (coming soon!)

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