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Reviews ? Mid- and Large-scale Continuous Flow Systems |
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Written by Administrator
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Sunday, 11 September 2005 |
Since the development of the first continuous flow system by Dr. Clive
Edwards at the Rothamstead Agricultural Research Station, many
mid-scale bins have been developed that utilize this design concept.
These systems are quickly gaining popularity. The savings in work
offered by their continuous flow design is greatly magnified as the
amount of material processed increases. This system design is now
almost ubiquitous in commercial mid- and large-scale vermiprocessing
systems.
In our last issue we reviewed two home-scale vermicomposting bins based
on the continuous flow concept. In this issue we review four mid- and
large-scale systems. Each of these systems uses a relatively deep
container fed from above, in which the composting mass sits upon a
raised floor made from widely-spaced welded wires (or rope in one of
the systems). Worms are added to the system and food waste is added
gradually, layered with bedding material. The system is continually fed
until the bin is nearly full. The worms generally move upward through
the feedstock / bedding layers and vermicompost is harvested from below
by scraping or cutting a thin layer of finished material from just
above the grill with the help of a rake or a hand- or
hydraulically-operated blade or bar.
It is interesting to remember that, despite the recent growing interest
in this design, the most common large-scale vermicomposting system in
use today is still the windrow.
Advantages and Disadvantages of Continuous Flow Bins
Continuous flow vermicomposting systems are becoming more and more
popular, and for good reason; they provide an ongoing flow of
vermicompost that's easily removed from the system without disrupting
the worm activity or requiring messy and time-consuming harvesting
methods. Because of their operating efficiency, these system designs
are becoming almost as popular as windrows for large-scale
applications. But, as with all vermicomposting systems, the continuous
flow model does have its challenges.
In an effort to simplify some of the research terminology the worms
most often used in vermicomposting acquired the name "surface feeders."
This led many to believe that their activity was always performed at or
just below the surface. This is not always the case, however.
Earthworms are oxygen-breathing, moisture-loving animals that require
organic material to be bacterially-active before they eat it. While we
prefer it when they remain near the surface, in the continuous flow
systems the worms will be found anywhere the environment meets their
requirements. In nature this is most often in the top few inches of
soil, forest duff, or drifts of organic debris, but in any system with
a free flow of oxygen, carefully monitored moisture level and abundant
supply of decomposing organic material earthworms can be found
spreading throughout the material unless the system is carefully
managed.
The exact rate at which raw feedstock can be added to a worm bed to
encourage the worms to concentrate at or near the surface, called the
loading rate, will vary depending on the feedstock being used,
temperature, moisture levels and the density of the worm population.
Proper loading rates require that new feedstock is not added until the
system has had sufficient time to consume the majority of the
previously added feedstock. Most operators of continuous flow systems
find that frequent additions of thin layers of feedstock (1"-2" deep
spread over the system surface), sometimes mixed with bulking agents
like compost, shredded leaves, cardboard, paper or straw, or covered
with an equally thin layer of these materials, demonstrate the best
results. They then make sure the worms are well into the previously
added feedstock before adding a fresh layer. Adding new feedstock too
early means there can be a build-up of unprocessed material that gets
buried more and more deeply under the new additions. Such a situation
means there will be sufficient available food deep in the bin instead
of being concentrated just under the surface, and the worms will spread
out to all the available food areas. Worm movement low in a
flow-through system causes vermicompost to drop through the mesh floor,
often before it's been sufficiently worm-worked. Further, when the
system is harvested, worms remaining low in the material will fall
through with the vermicompost and will either need to be harvested
using labor-intensive separation methods or will simply be lost to the
system.
Another of the challenges to any vermiprocessing system, regardless of
size, is the potential for heating in the feedstock. Bacteria are the
primary decomposers of raw organic matter and in an oxygen rich system
they produce water, CO2
and heat as byproducts of their activity. When raw material is added to
the system, especially in large volumes, the mass can support the
activity of billions of bacteria which can produce tremendous amounts
of heat that may be trapped in the system. Even small volumes of raw
material can heat if it contains sufficient energy to support high
levels of bacterial activity. The potential for heating makes
determining the system loading rate a bit more complicated.
It's important to understand that any worm bed is a system housing
thousands of different species of invertebrate animals and
micro-organisms, all of which play a vital role in the bin ecosystem.
While we call these "worm systems," the loading rate cannot be based
solely on the needs or capacity of a single organism in that system.
The system dynamic will include bacterial activity, which will have as
much impact as the worm activity. After all, bacteria will get to the
feedstock first! Systems that generate sufficient heat to deter worm
activity are being overfed for the design capacity, the type of
feedstock and/or the level of system activity. Design modifications,
like the addition of fans to remove excess heat can be made, otherwise
the loading rate will need to be decreased to a point where heating is
not a problem, even if that means feeding less than the worms are
capable of processing. Precomposting the feedstock before adding it to
the system can also help by decreasing the amount of energy in the
material so that heating in the worm system doesn't take place.
Feedstocks precomposted for 10-14 days retain plenty of nutrition for
the worms, but not so much energy that they are able to generate heat.
One of the advantages to the continuous flow design is in the ease with
which a continuous supply of vermicompost can be removed from the
system. However, harvesting of the finished material should not begin
until the system is fully charged, that is, until the system is nearly
full of material. Many operators have found that, along with
appropriate loading rates, a minimum depth of material in the system of
between 12"-18" will help to ensure that few, if any, worms will be low
in the bed and drop through, or fall out with the harvested
vermicompost. Once fully charged, vermicompost then needs to be removed
at a rate that maintains a relatively constant level of material in the
system.
Continuous flow vermiprocessing designs are arguably the most efficient
systems, in terms of time and labor savings, available today. But
regardless of efficiency or ease of operation, there is no design that
eliminates the need for careful monitoring and good system management.
A healthy dose of experience with worm systems and a thorough
understanding of system dynamics doesn't hurt either. Regardless of
design innovations, these are still biological communities that will
keep us guessing and keep us wondering at the marvelous efficiency with
which nature manages our world.
The Bins
Worm WigwamTM
Specifications:
Height: 36"
Diameter: 36"
Surface area: 7 ft2
Wigwam Features:
- Galvanized steel frame w/powder coat finish
- All recycled plastic
- Insulation and 110 volt heater w/ thermostat
- Insulation
- Full operating instructions
Worm Wigwam Reviews
The Worm Wigwam was the first mid-scale bin to appear on the US
market and has probably enjoyed more sales than any other mid-scale
worm bin. Designed in 1994 by John Gorman Sauvage.
From the outside the bin is quite handsome in green and black recycled
plastic. The bin uses a very heavy-duty galvanized steel grate as
platform for the composting mass. Plenty of holes low in the bin
provide aeration below the grate. Enough said, because our reviewers
are quite complete in their description.
Worm Wigwam review,
by Philip Jones
I bought my Worm Wigwam in April, 1999 because my daughter raises
chickens and has about 50 wintering over. Storing the chicken litter
until spring before composting it was not workable, and the continuous
flow design of the Worm Wigwam appealed to me because I have never been
a fan of batch processing. I live in Iowa and experience temperatures
from about 95°F (35°C) above in the summer to 20°F (-33°C) below in the
winter. I keep the WigWam in an underground "garage" along with the
chickens where the temperature ranges from about 25°F (-4°C) or 30°F on
the low side to about 85°F (-9°C) or 90°F on the high side.
The Worm Wigwam, ordered directly from the manufacturer, EPM Inc.,
arrived ten or so days after ordering. The instructions were easy to
follow and I had it assembled in about 30 minutes. Unless you have very
long arms, it will help if you have a helper to reach inside to tighten
nuts on bolts. The assembled unit is a "drum" three feet in diameter
and three feet high with two "lids" for the top and bottom and an
insulated compost chamber. The heart of the unit is an incredibly
sturdy epoxy-coated metal grate that sits on the inside of the bottom
"lid" and whose legs hold it about 16" or so off the ground. The metal
grate incorporates a series of scrapers driven by a worm gear mechanism
that harvest finished compost from the bottom of the compost chamber
when a handle is turned (about 95 turns for one pass). For those of you
who worry about these things, the compost chamber is 18" high, so its
surface area is approximately seven square feet and its volume a little
over 10.5 cubic feet.
The quality is absolutely first rate. The epoxy covering of the metal
grate, for example, eliminates potential problems with rust. All of the
fasteners provided are galvanized for the same reason, and one
particularly delightful feature is that the manufacturer includes extra
fasteners for those of us who might lose a piece or two during
assembly.
To start the unit up, I put several sheets of newspaper on top of the
grate, then added 6" of well-aged garden compost as a bedding material,
as EPM recommends. After this, I introduced five pounds of worms (EPM
recommends adding 15-20 pounds), followed by another one or two inch
layer of bedding material, a one-half to one inch layer of feedstock,
and a final one to two inch layer of bedding material. I added
feedstock and bedding material gradually in alternating layers as the
worms process the material. I added an additional five pounds of worms
one week later, and then again one week after that. Harvesting finished
compost begins when the bedding gets to about two inches from the top,
which took about two months in my case.
I've had three minor problems with the unit. First, I followed EPM's
recommendation to occasionally add moisture too enthusiastically and
found that if I put too much water in the top, it will flow out the
bottom and flood the garage every time. Second, as Kelly Slocum noted
in her review of smaller continuous flow systems, these units tend to
develop large air spaces above the harvesting mechanism, called
"cavitation," which defeats the purpose of the scrapers. After my
earlier experiences with water, I was reluctant to try Kelly's
suggestion of adding more water. Cheryl Paige suggested that I could
get rid of the air spaces by wiggling a garden fork around in it a bit.
Cheryl also suggested using some layers of hay every so often as kind
of a "net" to hold things up there until they get finished off.
Cheryl's suggestions worked for me. The third problem was mice. They
got in through the bottom "door" in the unit and tunneled around in the
compost chamber eating the worms. A couple of cats and three guinea
fowl (yes, they do eat mice) solved that one. One other tip: Monitoring
the temperature once or twice a week helps avoid over-feeding.
Right now, the Worm Wigwam is processing about 100 pounds feedstock
(combined waste plus bedding) a week. Although it is somewhat pricey
(currently $483 plus shipping), the quality of the grate and worm drive
mechanism are high enough to warrant that kind of price. I like it and
am glad I bought it.
Worm Wigwam Review,
by Ben DuBard
I work at the Rosewood Market, a 5,000 square foot natural food store
in Columbia, SC. We recycle all of the materials that our municipal
sanitation department will pick up, and we had wanted to compost our
organic wastes for many years. Finally, the opportunity arose, and in
1998 we began vermicomposting, using four Worm Wigwams and a
chipper/shredder purchased by our Department of Environmental Control.
Before long, we realized that trying to divert our entire organic waste
stream was a little idealistic, and the three other bins were sent to
different locations for additional projects. We currently have one
Wigwam that is fed approximately 15 pounds of whole veggie scraps a
week, with only occasional use of shredded paper for bedding.
I have encountered a few problems. First of all, whenever the
temperature gets over 80°F (27°C) the contents of the bin start to go
"thermophilic." In South Carolina that means from about April to
September. During those months it's difficult just keeping the worms
alive, much less feeding them any substantial amount of material.
In South Carolina, too, its always humid. I've never experienced a "dry
heat." Even the tap water is warm here, so evaporative cooling doesn't
work well, although I did freeze milk jugs with water in them to put in
the bin in the summer of 1998, but that was labor-intensive. For weeks
that year the temperature in the bin was over 90°F (32°C), resulting in
die-off. Last year wasn't so hot, and the bin went over 90°F only a
couple of times, and there weren't any apparent fatalities.
The second problem I enountered was that the finished product tends to
fall through the grate with worms in it. Normally some of this isn't so
bad, but when you're trying to build a population it can cost you time
picking the fellers out. Also the composting material tends to drip
"tea" into the collection pan at the bottom of the unit, making
additional drying of the castings necessary for our purposes.
Joan told me that on subsequent Wigwams, the company has added more
cross-members on the harvesting mechanism, in order to keep material
from falling through. When she moved the bins to other locations, she
added hardware cloth to keep material from falling through. Moisture
content seems to have little effect.
In spite of these problems I have enjoyed the project immensely. In the
past few months we have made excellent progress. The temperature has
remained stable and our worm population has exploded. We market the
finished product in mesh bags as compost tea, and we sell as many as I
am capable of bagging. This spring should see us increasing our sales
volume of compost and possibly generating some financial return for the
labor we have invested in this project.
The Wigwams were actually sent to other locations around the area that
wanted to have composting programs through the Department of
Environmental Control. When we began with four units, we would collect
buckets full of waste and waxed cardboard, which is not accepted in
recycling programs. I would shred the veggies and then the cardboard in
the Troy-Bilt shredder.
This process was extremely labor-intensive. It took me over an hour per
session to go through the entire process, tie up loose ends and clean
up messes. After a few months of this, Joan and I decided that it would
be better to run one bin well, than have three that barely survived.
Looking back, I can see that I had the tendency to overfeed, but I also
think that feeding rates can be extremely variable, and the optimum
feeding rate for a veteran vermicomposter might be a lot different than
that of neophyte. If I were to give advice to anyone who was put in
charge of a vermicomposting pilot, it would be to take feeding rates
with a grain of salt, and look out for the health of the worms first.
Now I simply collect the scraps and rotten stuff in a 7 gallon bucket,
and add it to the bin. I don't use paper bedding; I just dump it in and
spread it evenly.
The manual suggests taking the lid off to help with cooling, which I
did. Well, a hurricane came through once when I forgot to put the lid
on. It was surprising how well the worms took it. Now I use a slab of
styrofoam I found on the side of the road for the lid. It's white and
insulative (the stock lid is black), and it keeps Mockingbirds out, a
surprise I encountered when I left the lid off!
The ambient temperatures are down, and I think I will be able to keep
from over heating this summer by not keeping the unit over about 1/3
full, thereby reducing the thermal mass of the material inside. I think
the volume of rotting material is what causes the sustained
overheating, and adjustments to that might help. The instruction manual
recommends storing it under an enclosed area, something I didn't know
until we had received it.
I feel I finally have this system working well and know what a healthy
Wigwam should look like. Undigested material should make up a very
small portion of its volume, and I always wait until the scraps are
almost completely digested to add new matter. Now that I have this
experience, I wish I had the shredder and the other three bins back!
EPM’s Model 5-6TM
Specifications:
Width: 5'
Lengths: 6', 8', 16', 24', 32', 40', 48'
Surface area: 28 ft2
Model 5-6 Review,
by Steve Muller
Sampson Correctional Facility, NC
Here at Sampson Correctional Facility we're committed to "Leading the
Way" to Environmental Sustainability In State Government. Last year we
began an ambitious program that has been very successful and has
involved our whole institution. As part of that program, we've been
vermicomposting our jail's organic waste and waste paper for nearly a
year. In addition to the savings in disposal cost by vermicomposting
this material, we wanted to avoid the mess of trucking our wet waste
(and the occasional complaints to the EPA of leaking bags.)
We ordered two of EPM's Model 5-6 Vermicomposting System and one Worm
Wigwam which arrived in May 1999. Bruce Elliott, head of EPM, Inc.,
brought the bins and 200 pounds of Eisenia fetida worms, and we set up the bins and stocked them.
Once the system was set up, Bruce conducted a training session for
several of the staff and inmates that would be involved in the
operation of the vermicomposting bins. During this period of time we
also applied and got a permit to operate the vermi-composting bins from
the NC Department of Enviroment and Natural Resources. The next month
was spent perfecting the perfect recipe of food waste and shreaded
paper.
For this climate, at least, the bin is too deep. Its about 3' high from
the grate up to the top. Here, the system needs more surface area and
less heat. The organic matter in our bins became compacted and broke
the cranks, which we repaired. Since then, we only run the system half
full.
Here on the East Coast, we use salt-treated wood, treated all the way
through so it can withstand our large fluctuations in humidity. The
pressure-treated wood the bin came with isn't treated to the core and
when the bin arrived there were 2" gaps between the 2x12s. So we simply
added salt-treated plywood on the outside of the bin.
We redesigned the circulation system because the pile was becoming
somewhat anaerobic. We moved EPM's fan, setting it just above the grate
in such a way that it forces air out of the bin, which draws air
through the vermicomposting layer. Which this modification, we found we
could lower the system's temperature by 10°F (6°C). The systems are in
a climate controlled greenhouse with a large fan and eight foggers that
produce a very fine mist that also helps to keep the temperatures down.
Anyway, on September 15 Hurricane Floyd came through. We lost the lids
and so we put the same kind of plywood on as lids. We also flooded,
which we estimate to have taken probably 100 pounds. So, we bought 100
pounds of local redworms. Well, either they liked what we were feeding
them, or being local, were better adapted to our climate, because they
started eating more. But, we'd also made some changes and so we can't
say that it was just the worms.
After the flood our worms were eating 20 pounds of feedstock three
times a day. Some days we'd skip a day -- we didn't have any food
coming out of the prison. We've got the system running pretty well now.
We have no fruit flies or odors and we keep the whole greenhouse very
clean. We've even had a picnic in here for visitors.
In the same greenhouse we also run a Worm Wigwam. That's our test
(control) bin, where we try anything new to see how much heat develops,
how the worms like it, etc. It's interest that the Wigwam is handling
as much feedstock as each of the larger bins are.
We feed a mixture of shredded paper and post and preconsumer food
waste. We have a lot of shredded paper, because every desk has a paper
shredder
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Last Updated ( Sunday, 02 October 2005 )
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