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 Bulking Material 
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Joined: Wed Jul 16, 2014 12:03 am
Posts: 6
Location: Austin, TX
Post Bulking Material
Greetings all,
I have watched all of Jerry's videos about the tote composters he made and was wondering about bulking material. Several have mentioned using coconut coir, lava rocks, etc. However, I could not find any posts discussing optimal bulking material and its depth. I have gleaned from other posts that the coconut coir degrades and then clogs filter/drainage. Pine shaving carry the potential for sap. Jerry mentions using charcoal and I am considering using charcoal in my DIY composter. But would there be any ill affects from using charcoal for 100% of the bulking material? Is the relationship between the bulking material and feed layer a fixed number (ie, 2 inches of bulking material and 2 inches of feed) or is it a ratio (ie bulking material and feed layer each 50% of total depth)?

What bulking material have you used? How successful was it? Would you use it again? And, most importantly, what do you feel is the optimal depth for the bulking material?


Wed Jul 16, 2014 9:55 am
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Joined: Wed Apr 02, 2014 6:44 pm
Posts: 96
Post Re: Bulking Material
Hi GreenArrow,
For bulking material I used expanded clay ("Hydroton") in Jerry's largest bio-composter. Those BSF larvae only got fed waste vegetable pulp I get from my local fresh juice bar & found no problems at all with flushing the composter. The maturing larvae moved down in amongst the expanded clay & then the pre-pupae migrated out quite well.

Elsewhere in the Forum I explained my experience in more detail, including depth utilized & sample 2014 cost for that volume of expanded clay; it is re-usable. If you similarly will be dealing only with market stage vegetable/fruit waste then their water content readily percolates down for draining away (Jerry's design has a low point plastic ball valve); you will also be able to scrape off a decent amount of the larval non-utilized plant matter that eventually lays atop the expanded clay (plant carbohydrates feed bio-film microbial growth more so than a predominantly protein feedstock does).

Expanded clay is said to create more of a relatively alkaline pH substrate than an acid (low PH) substrate. Recently the Forum discussed whether pH was relevant to BSF larvae rearing; but I did no experiments on what the pH was down around the expanded clay bulking strata. Nor have I checked if once the expanded clay has been used for a larval growth cycle if there is any longer an affect on pH down in the bulking layer; this may be a factor of how extensively the used expanded clay pores are rinsed.


Wed Jul 16, 2014 4:53 pm
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Joined: Wed Apr 02, 2014 6:44 pm
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Post Re: Bulking Material
P.S. re: expanded clay bulking agent = before installing expanded clay it is absolutely necessary to wash off the production dust from the clay balls; if do not get rid of the clay dust it will settle out & form an immobile aggregation knitting together the individual clay balls. The best way to wash the dust off is to fill a basin/bucket with water & immerse the expanded clay in the water; then take out the clay & dump the wash water. Depending on the manufacturer's product one needs to repeat the rinsing several times.

Do not dump the wash water with it's sediment into any pipes leading to a septic tank or gray water holding tank; & do not dump that into any sinks because the sediment will settle in the "S" curve. It is possible to dump the wash water with sediment in small amounts at a time into a toilet bowel that is connected to a modern municipal sewage system. As it disappears pouring an already on hand large pot/bucket of clear tap water onto the the bowl's outlet helps the sediment empty out (flush that batch a 2nd time if sediment still seen).


Wed Jul 16, 2014 5:42 pm
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Joined: Wed Jul 16, 2014 12:03 am
Posts: 6
Location: Austin, TX
Post Re: Bulking Material
Gringojay,
Thanks for the info. I seem to remember seeing your posts about using hydroton. Glad it worked out for ya. I was researching aquaponics and was introduced to hydroton. Many people running aquaponic systems use river rock/pebbles as a replacement for hydroton since it is PH neutral. I am considering using it with charcoal for my bulking medium. What would you say is the ratio between your hydroton bulking medium and the feed layer?

Also, really appreciate you mentioning the washing. If I use charcoal and the river pebbles, washing will be critical. Perhaps Jerry could expand on the benefits to the BSFL he briefly mentioned in another post.


Wed Jul 16, 2014 9:38 pm
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Joined: Wed Apr 02, 2014 6:44 pm
Posts: 96
Post Re: Bulking Material
Hi GreenArrow,
I had close to a 50:50 ratio of expanded clay to feed substrate. If had used rock/pebbles it would have been awkward to move the unit for flushing; I'd easily prop up one end higher for fuller drainage (plant pulp throws off a high volume of water as rots) through the PVC valve.

Charcoal in soil is used to ameliorate low pH; usually explained due to how charcoal can start out at over 6.5 pH. Many extol how it's pores get O2 (oxygen) into the soil; however it's pores also can hold CO2 (carbon dioxide) & in a watery medium (ex: root zone) the higher the CO2 level the the lower the pH (ex: fresh water plant aquariums pump CO2 in to control progressive pH rise).

Now the question in my mind is if the degree of reduction of CO2 in the bulking substrate is of any importance. In other words might the late stage BSF larvae down in the bulking strata actually prefer a different ratio of CO2 to O2 than when they are young larvae. Elsewhere in the Forum I proposed that based on the visual observation of how late stage larval instars lingered down in the bulking strata of Jerry's bio-composter that this was a preference for lower oxygen (less partial pressure oxygen).

My point being that despite charcoal being good for soil growing this does not mean charcoal is ideal for including in the bulking layer, although Jerry's experience shows it can be used safely. However, no experimental comparison has been done to show whether late larvae thrive better with or without that extra CO2 (or other features) the charcoal pores hold back. Depending on the ratio of different sized pores in different sourced charcoal more or less molecules get tied up (adsorbed) by the pores. Larger pore size means less surface tension; which allows easier entry to water (H20) & molecules.

Protons adsorb to those charcoal pores; this extends to H20 protons & other molecule/compound protons. I did not see the late larvae in my lower strata of expanded clay moving upward to feed so they must have been dining on what came down; therefore I wonder if adsorption might take some larval nutrients out of play. In soil plant growing adsorption by charcoal is generally beneficial because it sequesters phenols (root inhibitors) & competitive minerals of preferred nutrient uptake; maybe the late larvae would also benefit from reduced level of free floating phenols released from rotting plant matter.


Thu Jul 17, 2014 1:06 am
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Joined: Sat Mar 05, 2011 11:35 pm
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Location: Central Florida, USA
Post Re: Bulking Material
I still like pine bark (not shavings) the best, but I haven't tried hydroton which seems like it would be excellent. What makes the pine bark attractive is mostly its shape. The flatness of the pieces help create good air pockets throughout the waste. In one test I measured the air spaces in the waste at approximately one third of the total volume. I think those air spaces are the main reason this design is so easy to keep in a balanced state. Other than targeting a certain shape, I think bulking material should be porous. Other than that I don't know how to compare the chemistry of them.

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*I'm not an entomologist, and much of what I write about BSF is an educated guess.


Thu Jul 17, 2014 1:53 am
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Joined: Sat Mar 05, 2011 11:35 pm
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Post Re: Bulking Material
I've been using and recommending a total bulking volume of 1/3-1/2 of the wet capacity of the composter. I think you could use less without diminishing efficiency, but I don't think having extra bulk hurts efficiency. More can always be added, and if you're using something large like pine bark some can also be removed relatively easily if space becomes an issue. As I mentioned above; my goal is to have a lot of air space in the waste. For me, the right ratio of bulk/waste is whatever achieves and maintains that. The best volume of bulk will probably vary with each material.

I've been testing corn cob pieces for several weeks, and so far I can say that the smaller size results in slower drainage. Compared to systems that use no bulking material it still drains quickly. I haven't tested that unit for percentage of air spaces, but maybe I'll do that soon.

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*I'm not an entomologist, and much of what I write about BSF is an educated guess.


Thu Jul 17, 2014 10:27 am
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Joined: Fri Aug 22, 2014 5:04 pm
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Post Re: Bulking Material
Has anyone used shredded trees from the power line right-of-way people?


Sat Aug 23, 2014 12:03 am
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Joined: Sun Aug 24, 2014 7:41 pm
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Location: Mississippi Delta
Post Re: Bulking Material
The best bulking material I tested is polyacrylamide, don't need to worry about drainage. Roughly in the 6 gal Jerry composter a thin layer of dry polyacrylamide at the bottom, 1/3 inch, might be enough. The bestest result, soaking polyacrylamide with a culture of Bacillus subtilis.


Sat Aug 30, 2014 8:37 am
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Post Re: Bulking Material
arkbilly, I haven't tried that material. My favorite so far has been smaller sized pine bark mulch because of the size and shape. The goal is something that will encourage the formation of air pockets in the waste.

Alfredo, that material sounds very interesting, but I don't understand how it would function with my drainage system. I assume you use it in a different design. At 1/3 of an inch and being a gel, it doesn't seem to fit the concept of a bulking material. It seems like the anti-bulking material. ;) At any rate I'm sure you've had good results with it.

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*I'm not an entomologist, and much of what I write about BSF is an educated guess.


Wed Sep 03, 2014 11:17 pm
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Joined: Thu Jun 11, 2015 4:48 pm
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Location: East TX
Post Re: Bulking Material
I think I'm going to try pine needles... The kind that are about 8 inches long, since we have lots of those around here and they decay very slowly and leave lots of air pockets and can be easily fluffed... unless someone wants to point out why that is a bad idea...


Fri Jun 12, 2015 1:23 am
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