Instructables
Picture of Building a forced air composting system
These build instructions assume you already have a static compost pile that you’re trying to renovate or already have an understanding of composting or understand how to build a static compost pile. There are a ton of very good resources on why aerating your compost is beneficial and they’re complete with graphs and studies from Universities. What I found was that none of them had actual plans on how to build one.

In very basic terms the microbes that decompose the waste feed on oxygen, and they need a lot of it. Tumbling composters are good but studies have shown that the oxygen levels decrease within minutes of the action stopping. Spinning the tumbler once or twice a day does help to make compost decompose faster, but most people aren’t consistent in the frequency require to spin the bin for the weeks or even months required to finish compost. If you search for “compost aerators” you’ll find tools, which look like dirt corkscrews, but honestly if you’re not going to spin a tub twice a day, every day for a month and a half, using a dirt corkscrew for the same time frame is not realistic.

Also, Tumblers are also too small for large home composting, or small farms or businesses. A single horse can produce 50 pounds of waste a day. A tumbler composter may be able to only hold a single day or two of manure. So if it takes says 2 months for a tumbler to fully compost when turned every day. That would be 40-60 tumblers per horse, turned every day. Don't get me wrong, I love tumblers, I have one for kitchen waste, but for horse/chicken manure, grass clippings, and brush clean up it all goes in to the aerated pile.

Forced air systems allow people to compost who would otherwise have to throw the waste away, or simply make their existing systems more efficient and maximize the available space as a well set up forced air composting system can reduce the time to finished compost to 3 – 5 weeks. Yes, you read that correctly, less than or about a month.

If forced air systems are so great why doesn’t everybody have one ? Simply put, they’re unneeded for the average household, and for those who could benefit from an aerated composting system, those systems usually are too expensive (Custom 3 bin aerated system holding 400 cubic feet starting at $5,000) and/or are too large or overboard for what is needed; i.e. a small family hobby farm doesn’t need the smallest industrial composting system, when the smallest system is $100,000 and 5,000 cubic feet of compostable waste. This is a scalable middle ground between a backyard worm bin and a $4,000 custom set up or $100,000 industrial system.

 
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vespaskank, you gave me a good idea regarding ordinary electric blower instead of electric motor! Thank you. I'm a guy from cold =)) and distant Russia :P
I surfed internet and found that :
1) the microbes could require a volume of air > 20 times the volume of compost, every hour (look at the pic with pyramid and notes for it at this link: http://www.magicsoil.com/Research/)
2) the oxygen level in the pile drops off very quickly - often to less than 1% within 30 to 45 minutes (source: http://www.o2compost.com/content/Secret.htm) and the previous source says that oxygen drops down even faster - in 15 -20 minutes.
I have a plastic container of 1 cubic meter, so I suppose that every hour I should blow in 20 cubic meters in the container. it's easy to calculate that if I have , for example, a blower of capacity 228 m3 in hour tha means I should use it 5.2 minutes in hour. + it's essential to divide this 5.2 minutes to have 4 breaks of about 15 minutes or a bit less.
3) It seems that volume of blown in air depends on the moisture content in the compost components....and it often happens that 20X (to a compost's volume) volume of blown air inside can dry the compost a lot. and what if I have a chance to water a compost once a week ? Should I reduce blown air? I think so. But in this case what's the point to blow the air inside if we have 50% of the whole composting period CO2 existence (= anaerobic bacterias) inside. Productivity in this way fall down to 1/2.

May be it's better to make a "skeleton" of drilled and connected vertical and horizontal tubes inside the composter and regulate the draft (it's created by heat that's done by bacterias, it's a bit more advanced than guys do in Aerobin 400 ) (you can look at Aerobin here: http://eartheasy.com/yard-garden/composting/aerobin-400-insulated-composter-15-cubic-foot-133-gallon-compost-bin )
I still have a question - Is it possible to regulate the speed of air flow/ time of its work properly not to dry the compost and have FAST composting speed. Or it's better to make a passive ventilation with tubes (I mean for summer season use)? Do you have an idea/ experience of your own? Thank you !
;)
rimar20003 years ago
Very good project, congratulations!
vespaskank (author)  rimar20003 years ago
Thank you for you feedback!



Step 10 "Setting up the automatic timer" briefly talks about timing:



I recommend starting out with twice a day for 5 to 15 minutes, it depends on the timer you bought and the settings you have available. Originally I had a fully adjustable timer and had it set, to run 10 minutes 4 times a day but I found it dried out quickly and it never maintained a core temp of 140 degrees.



Through trial and error of compost troubleshooting I’ve gotten adjusted to work for twice a day for 15 minutes and it now it keeps a good moisture level, no smells or odors and has a consistent all over temperature of 140 degrees which means good microbe activity.




More specifically Ismith254, I've found the you may have to change the frequency depending on the weather, for example I live in Seattle where it rains a lot even in the summer and even though my piles are covered there is some leaching and leaking, so I find that if I add another internal of even 5 minutes it will help to aerate and dry the pile out enough to keep the balance I need.



Again it really is troubleshooting and trial and error based on your setup and the number of holes in your pipe. For some people and climates every other day for 5 minutes will be enough, and for others 2-3 times a day for 5-15 minutes may be better to keep the right balance.



Just play with the time and moisture levels until you find out what keeps your compost thermometer at 140 degrees continuously. Hope this helps!
Thank you, somehow I missed that part. Thanks for sharing the knowledge!
lsmith2543 years ago
I scanned through everything, and could not see anything about how long you leave the blower on? Is it only for a few minutes a day? Thanks!
vespaskank (author)  lsmith2543 years ago
Thank you for you feedback!

Step 10 "Setting up the automatic timer" briefly talks about timing:

I recommend starting out with twice a day for 5 to 15 minutes, it depends on the timer you bought and the settings you have available. Originally I had a fully adjustable timer and had it set, to run 10 minutes 4 times a day but I found it dried out quickly and it never maintained a core temp of 140 degrees.

Through trial and error of compost troubleshooting I’ve gotten adjusted to work for twice a day for 15 minutes and it now it keeps a good moisture level, no smells or odors and has a consistent all over temperature of 140 degrees which means good microbe activity.


More specifically Ismith254, I've found the you may have to change the frequency depending on the weather, for example I live in Seattle where it rains a lot even in the summer and even though my piles are covered there is some leaching and leaking, so I find that if I add another internal of even 5 minutes it will help to aerate and dry the pile out enough to keep the balance I need.

Again it really is troubleshooting and trial and error based on your setup and the number of holes in your pipe. For some people and climates every other day for 5 minutes will be enough, and for others 2-3 times a day for 5-15 minutes may be better to keep the right balance.

Just play with the time and moisture levels until you find out what keeps your compost thermometer at 140 degrees continuously. Hope this helps!