Bio-composter - filterless drainage methods and observations
6 gal composter - inside 1 800px.jpg [ 281.69 KiB | Viewed 11723 times ]
Here is the introductory post on this subject from the blog:
Good drainage is key to a balanced BSF system
When I refer to a “balanced BSF system” I mean one that promotes aerobic bacteria (thrives in oxygen) and discourages anaerobic bacteria (thrives in the absence of oxygen). A nice benefit to an aerobic system is that it smells neutral, or even good, depending the waste being processed. Anaerobic bacteria are associated with foul, sewer-like odors which are a sign that a composter needs attention. To maintain an aerobic environment in our composters, we need pockets of air throughout the waste. The problem is that BSF castings are so fine, and they generate such a large volume of them, that air pockets are filled up over time. This dense, oxygen-starved waste usually becomes anaerobic. It's common for a BSF system to seem fine when observed at the surface, but if you dig down a bit you’ll often find stinky anaerobic waste. Besides being less efficient, it’s usually just a matter of time before the condition worsens. I believe I’ve solved this problem.
The combination vertical/horizontal, slotted drain system on my BSF bio-composter allows the operator to easily flush out the fine BSF castings which results in an oxygen-rich environment, and which also produces a potentially valuable liquid fertilizer as a byproduct.
This BSF composter is unique in that it is designed to be flushed with water on a regular basis. I've been testing this system in various composters since April 2013, and the results have been excellent. Passing a large volume of water through the waste rinses away much of the fine BSF larvae castings (poop), and also encourages any dark mature pre-pupal larvae to migrate out of the waste, and into the collection canister.
Filters don't work
- Many BSF composter designs that I've seen attempt to prevent the larvae from passing into the drain outlet. This system encourages the larvae to enter it. Screens and filter mediums will rarely prevent larvae from passing into the drain outlet, and if the filters are fine enough to stop the larvae, the fine mesh or filter medium will quickly clog with BSF castings under normal use. In my experience, screens and filter media do not work for that reason. Also, since the filters/screens in these systems are usually located at the bottom of the waste, it is very inconvenient to access the mesh/filters for cleaning or replacement.
EDIT June 2014: I'm still using pine bark, but have become aware of an issue with the release of sap/resin in some batches. If you're using one of my bio-composters, you can dissolve pine resin with Dawn Ultra dish soap. A description of the pine bark issue and the Dawn Ultra treatment can be found here: LINK
I'm currently testing alternatives to pine bark, including common wood mulch, and using all hardwood lump charcoal. I used medium coconut husk (coir) chips in the past with good results, but after several months it tends to shred and slow down drainage.
This unique filter-less drainage system is designed to be used with some type of bulking material, and our current recommendation is pine bark mulch
. Natural lump charcoal
can be combined with the bark, and this year I will be testing a unit using only charcoal as the bulking material. In the past I've used coir (coconut husk) chips (not the powdery stuff) which worked well for a several months, but the larvae and the water eventually will shred it to the point where it's less effective than bark or charcoal. Other materials that may work are wood mulch such as cypress or eucalyptus, or corn cob bedding, but I haven't tested these. The basic function of the bulking material is to create a matrix where pockets of air can be maintained which promotes aerobic conditions. I call this a filter-less system, but it's probably more accurate to say that the bulking material itself is a filter medium.
The slotted pipes in this system allow the larvae to pass freely, into and out of, the drain plumbing. The main benefit is that the larvae constantly create tunnels in the waste that terminate at the slots in the pipes. This enhances the rapid drainage that carries the fine castings out of the waste. The amount of air space created in the waste/castings using this system is substantial. I recently measured the volume of castings in one of my 6 gallon composters and it was approximately 4 gallons. I then added 1.5 gallons of water which came just up to the top of the waste. From that measurement we can conclude that of the 4 gallon volume of waste, 1.5 gallons, or 37%, of that volume was air space. Not only is there a substantial percentage of air in the waste, it is distributed throughout the waste, even at the lowest levels. Due to the large volume of air space it is very unlikely that there will be problems with anaerobic bacteria spikes. Every other composter design I've worked with had a significant presence of anaerobic bacteria in the lower levels of waste.
The frequency of flushing will be determined by a few factors including the type of waste processed and the quantity of waste. Flushing will remove BSF castings, but it can also rinse out soft food waste that the larvae would otherwise eat. For example; if you recently fed some old oatmeal cereal to the colony, some of it might be flushed out of the system, and if there wasn't a buildup of BSF castings at the time then there would not have been much advantage in flushing. Under most conditions I would think that once per week would be a minimum flushing routine, with increased frequency as needed. One way to determine if you need to flush is to observe the waste by looking through the clear wall of the composter (see photo below). If very few air pockets are observed it might be wise to increase the frequency of flushing. Another way to judge is to observe how quickly the liquid empties when the composter is flooded, and then the valve is opened. Ideally most of the effluent (liquid waste) should drain out in several seconds. If your unit drains more slowly you should probably try flushing more often.
There are almost always larvae that are flushed out of the composter with the water and fine castings. To deal with that I usually strain the effluent through a fine mesh kitchen strainer placed on top of the bucket used to catch the liquid. The larvae collected in the strainer can be returned to the unit, fed to animals, or added to a new unit to help establish a new colony.
Processing typical household food waste usually generates at least a small quantity of liquid on a constant basis. Often you can observe larvae trapped in the clear drain tube even when you haven't added any water to the unit. It's a good idea to drain the accumulated liquid every day if possible, using the same strainer technique, because the trapped larvae can eventually drown.
Sometimes, in addition to juvenile larvae, you'll see mature (dark) BSF larvae washed out of the system. Instead of separating mature larvae from juveniles, I usually just put them all back into the composter where they can eventually follow the intended path up the ramp.
Typically, after flushing I will leave the drain open for one or two hours before closing the valve. You can also flush the composter in the morning, let it drain for several minutes and then complete the draining process later in the day. Either way the amount of "hands on" time with the process should be no more than 5-10 minutes. In my opinion, this regular maintenance is far more desirable than dealing with spikes in the population of anaerobic bacteria.
Sometimes the drain plumbing can become blocked with fibers, and also with larvae that congregate in the pipes. These blockages are usually very easy to clear, and sometimes it's enough to simply flood the system briefly and open the valve. Other times it requires a little more effort, and the best method in that case is to direct the open valve into a bucket, and shoot water from a garden hose into the top of the vertical pipe. Typically, a minute or two of work results in a completely clear drain.
There are some fine points to working with the drain tube. Sometimes, as a blockage moves down the tube, it will stop at the valve instead of flowing through it. That's due to a slightly smaller diameter at the transition from the tube to the valve. This is easily cleared by raising the valve above the water line (visible in the clear tube) and temporarily removing it from the tube. Once the valve is off, the tube is lowered and the liquid (and the blockage) are directed into a bucket. This is accomplished by pulling the valve off with a twisting motion. The valve is held in place with friction, and it can easily be removed and replaced. The same technique can be used to remove the other end of the tube from the composter, but that's not usually needed.
The effluent seems like it must be a great resource for gardeners. While I haven't run any controlled tests yet, I've been pouring it directly on my ornamental plants all summer, and they look great. I don't know much about worm or compost "tea", but I hope to use the BSF effluent to experiment with fertilizer tea in the future. Next year I plan on running some controlled tests using the liquid as a fertilizer. Composting with BSF results in very little soil produced, but I hope that the large volume of liquid byproduct created by my flushing procedure will compensate for that by generating a large volume of good fertilizer.
The photo below is of the composter that I've been feeding 1.5lbs/.71kg of waste to on a daily basis for 38 days. It was established about 6 weeks before that. I estimate that I've fed this unit about 90lbs/40kg of waste since August 1st when I started it. After processing all of that material, it still has large air pockets very near the bottom. Flooding the composter forces the air in these pockets out, which is replaced with fresh air as the unit drains.
6 gallon composter - air spaces and larvae.jpg [ 217.6 KiB | Viewed 11723 times ]