Building a domestic 100-200L anaerobic digester composter

Hello all,

I have just moved to a small cottage with a narrow garden. I have decided against a compost bin for kitchen waste as I think my neighbours will find the smell offensive and the thousands of tiny winged insects that lived in the bin at my old place would certainly find their way into my house and the studio at the end of the garden and my neighbour's properties.

Presently I am collecting my kitchen waste and burying it in a different spot in the garden every time it is full. This works fine but I plan to build 4 or 5 big planters to plant up next April and I want to start saving my compost for them.

I am thinking of building an anaerobic compost digestor to keep the smells and composting process contained. Something along the lines of a fairly airtight box with a tap at the bottom for occasional drainage, and a brewers airlock in the top to allow gases to escape. What you guys think? I can't find anything like this for sale and wondering if there's a good reason for that.

thanks

Hagop

Hagop,
I would be cautious about making any kind of anaerobic type environment while composting. The kind of bacteria involved could be pretty nasty. If your concerned about odor and the neighbors this might be a whole lot worse than a good old fashioned turned compost pile. Think septic tank. When you crack the lid on that thing anyone down wind will know. Just my opinion though.

Mark

As Mark above said, cracking your digestion vessel open to monitor the contents *will* release disgusting septic tank-like odors into the vicinity that you wouldn't otherwise have with an aerobic process. Other than the odor and difficulty monitoring the pile without sampling said odor, I imagine it's not as popular because it doesn't destroy pathogens or render seeds inert, it takes much, much longer to finish a batch, and you can't really add anything to the batch after it's started. When an aerobic pile really gets going, you can throw new material into the center of the pile and not worry about it.

However, if local regulations prevent an open-air pile and you'd otherwise be "shipping" your unused organic materials elsewhere, anaerobic decomposition is a good option. I would contend that a little civil disobedience is the best option given that a properly maintained aerobic pile smells like fresh fall leaves at its worst and nothing at all at it's best.

I been experimenting with anarobic composting in 5 gal buckets and its working great! I have 2 with lids and have put everything in them. Food scraps, rinse water from the milk pail, whey, pee, coffee grounds, a beer, a cup of Epsom salt, handfull of bone meal, leaves of nitrogen fixers, etc... And while it does stink when open, its brief and a cup of that liquid diluted in 2 gal water poured on all my growies weekly has made them grow like CRAZY! I open daily briefly to ad stuff an the stink dissipates in a few seconds....

I agree: I think you can find various better solutions than anaerobic digestion for kitchen waste.

Anaerobic digestion produces methane, a far more potent greenhouse gas than CO2, and methane smells like farts, much worse than aerobic composting. Unfortunately your kitchen is unlikely to produce a useable amount of methane for fuel.

Our guts are anaerobic, and many gut pathogens can survive anaerobic digestion happily, though there is little reason to think there might be pathogens in your kitchen waste (as long as you are not going to add toilet waste to it). Anaerobic digestion is said to not generate much heat and thus doesn't kill off seeds, so you may find zillions of melon and tomato starts in your garden after using the compost.

It is also said to be much slower than any other form of composting, so you may find recognisable chunks of uncomposted stuff in your compost.

I have two possible ideas I might try if I were you. Lots of people swear by worm farming instead of composting, say it doesn't generate those little flies or smells, and you get the best compost and faster than any other method. I haven't done it myself, and worms are picky and refuse certain foods, so you might still be burying your onion skins and citrus peels in the garden anyway.

Another method being done at my family's house in a damp climate in the US to keep pests out, is to put the kitchen scraps first into a perforated metal garbage bin and cover every contribution with leaves. Raccoons and other pests can't get into the metal can. After a while, when the food scraps are already half rotten, we empty it onto the main compost heap and cover with more leaves. Because every contribution is covered with leaves, there aren't many or any little flies and gnats.

Thanks everyone for your opinions and feedback. All very helpful.

What about bokashi? Admit I've not tried it- but it claims to be a way of fermenting kitchen waste in a bucket with no smells.

Looking into Bokashi. Looks  great.

I'm looking into bokashi now as well! Most of our stuff goes into a 'hot composter' (wheelie bin lined with insulation)- but now we've got cats and we find the leftover cat food (of which there isn't much, admittedly) makes the compost bin smell! In our slow composter it gets dug up by creatures.. so bokashi might be an idea.

It is possible to have an essentially smell and fly-free compost bin. If it smells or has flies, add more cover material, such as sawdust, hay, or dried leaves. Pull the cover aside and pour new compost in it, then re-cover. I made my bin with 4 pallets, just make sure they aren't pressure treated, and I use leaves from the yard. Check out The Humanure Handbook. I have stood right next to humanure compost bins and not noticed any odor or flies before. You have a layer of spongy materials like leaves on the bottom, sides, and top of the kitchen scraps and compostables. These filter out the smell and bugs, and make a nice insulated aerobic but moist environment for thermophilic composting. I've read you can even add small dead animals to it. When the cats bring me a rodent present, I feed it to the compost pile now. A year of thermophilic composting will kill any pathogens, though I know some folks who compost their humanure for three years. I haven't started doing humanure composting yet but everything else goes in there and if it smells I add some leaves and the smell goes away.

Have you looked at worms?  You can have more dry matter to reduce smells and cover smelly problems.  Worms running properly produce almost no odor.