Earth Tub Frequently Asked Questions:
(with answers provided by Green Mountain Technologies [GMT]--producers of the Earth Tub)
* Basically, how does it work?
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* Basically, how does it work?
The unit consists of one 7'6" diameter tub and a biofilter
(for removing odors). The techs suggest a 12' square area to allow
for operation. Our current plan is to put it behind a college. The
labor involved in the project is:
* Does it smell?
The Earth Tub is a sealed, aerated container with a biofilter. Since it is aerated, most of the activity in the tub is aerobic (bad smells happen when it is anaerobic). For the few random parts that become anaerobic for a short time, there is the biofilter which "digests" the odors from the exhaust air that is passed through it. When I pressed the company on this, they said their testimonial is that the EPA main office has one operating right below a frequently opened window. During the curing process, if the process is done properly, it should give no odor. If it is done improperly, it would give off some ammonia. The finished compost will have the mild smell of humus (like a damp forest floor--much better than the pungent mulch they are using on campus now). Since it is sealed, it also keeps pests out.
* How is it powered?
It is electrical and so produces no fuel exhaust.
* How would compost operations work with a single Earth Tub?
Regarding composting with a single tub and the issue of the curing period. At the other sites which are composting with a single unit, the typical daily load is 40- 100 lbs per day. At these levels of loading it takes the following times to fill the tub:
Lbs per day Approx time to fill tub
Several of these sites are colleges or schools and often have a down period which they can time their final cooking process in the tub. HOWEVER --- there is an excellent way for your potential users to deal with this issue in a continous flow. Consider it as the same phenomenon as sourdough starter. The analogy is fairly accurate.
The compost undergoes an incredible volume reduction as it cooks over time (Iím sure you have observed this). For a business adding 50lbs a day , their tub would be full in approx 3 months or so at which point nearly material is well digested compost, except the fresh food just added. That volume is quite small relative to the larger mass of material. The customer then unloads _ of the material from the tub, and can begin adding as usual for another 2 months or so. The material that has just been removed is highly decomposed and nearly stable. It can be taken elsewhere to cure, or even better, filled into large plastic mesh bags, similar to white sandbags. The bags breathe and shed moisture. The bags can be stacked and stored for a short period or distributed right away with the notice to let them sit for a period before using. To avoid getting big hunks of raw food in that mix being emptied, the site would add food to one half only for a couple weeks and discharge the finished compost from the opposite door.
The 50 lb/day (or anyother figure I've given you for a daily load capacity) is based on the foodwaste portion only. Typically we load up the ET(Earth Tub) half full of bulking agent and then continually add foodwaste. Suprisingly, the compost reaches temperature within 2 or 3 days even though the C:N and moisture ratios are way off. I was quite impressed by this. This is somewhat attributed to the fact that the ET is not unloaded 100%. A small amount of material is usually left in the tub to serve as innoculant for the next batch. The sourdough theory again.--Stephen LaMarca, GMT
* How would compost operations work with a pair of Earth Tubs?
First calculate the amount of material to be composted. We calculate the amount based on the foodwaste portion; the bulking agent (wood & leaves) is added on 1:1 basis roughly. To compost 250 #(lbs) of foodwaste every day (7 day week), two Earth Tubs would be used. If two Tubs are used together, one Tub is fed continously till capacity is reached. Each Tub has a 150# /day capacity, but two units being used together raises the single unit capacity to 300#/day; one unit is getting all of the daily load and the other receiving none, the average still stands at 150#/day per unit. Fill the first Tub till capacity is reached, approx 3-6 weeks, and then "cap" that unit off; don't add any new material. Proceed to the second empty Tub, and feed it actively with the daily load. The first Tub continues cooking away with its contents and getting mixed up once a week. After 2-3 weeks, the compost will be fully decomposed and ready to unload. Unload the first bin. When the second unit reaches capacity, 3-6 weeks, the first is empty and ready to become the active bin again. Proceed in this rotation. --Stephen LaMarca, GMT
* What pest control is needed for the curing
If the material is relatively mature, pest control for the curing piles is minimal. We have had material curing at sites in New York City and have never heard of any problems with pests there.--Greg Howe, GMT
* What is the delivery time?
Typical delivery is 4-6 weeks depending on stock on hand upon receipt of order.--Stephen LaMarca, GMT
Delivery time is about 4 to 6 weeks from receipt of a purchase order.--Greg Howe, GMT
* What is the life-span of a tub? What is the longest operating tub?
Lifespan...15-20 years? The plastics not going to break, the auger is Stainless steel, the auger motor and gear box are industrial quality and run very seldomly (10 min/day). The blower motor runs continously and may burn out after 5 years and need replacment. I'd say the lifespan is quite long. It basically a giant kettle with a really sturdy mixer. Not a whole lot of moving parts. Longest Tubs in operation, I believe is about 3 years (when we started making them in their current production form). Prototyping and development had occured for a few years before that.--Stephen LaMarca, GMT
The lifespan of a tub is estimated to be about 10 years. The longest operating earth tubs have been in the field for about a year-and-a-half.--Greg Howe, GMT
* What about pathogens? What is the danger from pathogenic contamination due to post-consumer composting?
Introduction of pathogens (salmonella, e-coli, etc.)
is possible with post-consumer composting. However, our system thoroughly
addresses this concern. During active composting the temperature
within an Earth Tub is between 55-65 Celsius (135-150F). The vessel
is fully insulated. We have received Health Department approval
for a site using Earth Tubs here in Seattle. They approved non-restricted
usage (on-grounds, distribution to shoppers) and approved limited addition
of grease and meat products.--Stephen LaMarca, GMT
None of the tests conducted on finished compost from an Earth Tub have detected any pathogenic contamination.--Greg Howe, GMT
* Is it possible to lease an Earth Tub for a trial test?
We are willing to use commercial leasing as part of a sale. Direct leasing from GMT is possible but not typically cost effective.--Stephen LaMarca, GMT
A lease arrangement can be arranged. Leasing arrangements are flexible. A minimum lease would be 2 to 3 months. Generally, we would require that a leesee pay for shipping to and from the site. --Greg Howe, GMT
GMT is now working with First Interstate Leasing to provide a Lease Program with a 10% buy out End of Term. Estimate of monthly payment for one Earth Tub:
--Dick Lindow, BioResource Management (distributors of the Earth Tub)
* What exactly is the curing process? It shouldn't take six weeks if the compost is just cooling off. What is happening chemically in the compost during this period?
In the curing process the compost is aging like a fine wine or "mellowing" like a soup. During this process period, the compost is chemically changing the material to more stable compounds. Fresh hot compost out of the Tub is thoroughly decomposed but has a degree of phytotoxicity (toxic to plants), because the compounds are very "raw" and have just been active. As the compost cures microorganisms continue to convert the organic materials and acids into forms that are not harmful to plants. Curing is not necessary if the compost is to be used directly as a thin mulch (around trees or shrubs) because it is not directly in contact with roots.--Stephen LaMarca, GMT
During the curing process the ratio of carbon-to-nitrogen comes into balance as does the pH that shifts to neutral. Curing will further the decomposition of resistant compounds, organic acids and large particles of material and increase the concentration of humus. The overall quality of the compost will be greatly improved by a thorough curing process. --Greg Howe, GMT
* When the material comes out of the Tub and is going to be cured, what condition is it in (is it like soil?).
Directly out of the Tub, the compost is still hot, moist and very decomposed (brown and crumbly). All foodwastes and such are completely broken down. The compost does not change physical texture during curing.--Stephen LaMarca, GMT
The condition of the material upon discharge from the unit will depend on the characteristics of the input materials, the duration it has spent in the unit and the management of the unit. To make best use of the unit you will want to move a lot of material through it in a timely manner. This will probably mean that the discharged material will not be very mature and will benefit from the curing process.--Greg Howe, GMT
* What are the odor issues with the curing process?
The compost is still subtly active during curing and requires air for the respiration of the microorganisms. The compost will not generate odors unless completely covered with plastic or sealed into vessels.--Stephen LaMarca, GMT
If the material is not decomposed well before it is discharged it is likely to release ammonia during the curing.--Greg Howe, GMT
* What are the odor issues with the finished product?
None.--Stephen LaMarca, GMT
If properly mixed in the tub and cured then the finished product is done.--Greg Howe, GMT
* What other applications are possible with the Earth Tub?
The Earth Tub can also be used to process animal manure and biosolids (sewage sludge). It will compost anything organic really. By shortening composting times, the Earth Tub can be used to preprocess materials or to run a quick heat compost process. Some universities also use the Earth Tub to perform research and use for education.--Stephen LaMarca, GMT
The system is very efficient as a mixing unit.--Greg Howe, GMT
It seems that we should also be able to use it to compost bathroom paper towels.--Ryan McMullan, Rice
* What are the electrical requirements of the Tub? (Voltage, kW-h, etc.)
The auger motor can be installed with single phase or
three phase motors.
The auger motor can run on single or 3-phase power. 120V,
208V, 230V etc.
* What are the installation requirements? How much space is needed for a full set up (what is the system's footprint)? What additional equipment is necessary?
The cover measures 7'6" in diameter and the containers sides taper down to a base that measures 66" across. This tapered design facilitates the unloading process. The overall height of the container is 48". The loading hatch is 36" by 29". The discharge doors are 22" square. The bottom of the doors begins 14" from the ground.--GMT Earth Tub Specifications document
The units should be situated near to the source of the
materials you wish to compost and preferably near to a sanitary sewer
or suitable drain for the leachate that is generated.
* Who is your contact at A&M University that I may contact? What about the University of Georgia?
The University of Georgia is currently ordering 6 Earth Tubs. They are not yet installed. UGA already has a whole research control system they purchased from us last Nov.--Stephen LaMarca, GMT
You may contact Mr. Guy Stone at firstname.lastname@example.org
* Can the Earth Tub handle leaves-only loads? Would anything have to be done differently to accommodate for this?
Leaves only would be very possible assuming they were adequately moist. It may be necessary to add water to reach the proper moisture. They would compost fine and reduce volume tremendously but may be slower than a foodwaste mix. I would be very interested in the results for such a trial; it may not take any longer. I would suggest keeping 1/2 yard of compost from a previous batch in the Tub to serve as a microbial catalyst. --Stephen LaMarca, GMT
We do not recommend mixing only leaves in the system. Leaves have a tendency to mat together. Any leaves going into the system should be mulched prior to adding them in.--Greg Howe, GMT
* How does the biofilter operate? How often must it be replaced/recharged? With what?
Biofilter is simple and low tech, but does a real hi-quality job. It is a vertical column with a mix of wood chips (for porosity and surface area) and aged compost (for microbial activity). The material acts as a filter sponge and the organisms "eat" any possible odors. Sometimes, lime is periodically added to the filter to keep pH up. Maintenance= keeping it moist (keeping covered in summer) and recharging about once a year with the mix described above. --Stephen LaMarca, GMT
We blow exhaust air from the Earth Tubs into biofilter containers that neutralize odorous compounds before releasing the exhaust air. The material in the filters is a mix of 80% wood chips to 20% compost. This material should be changed only about once per year.--Greg Howe, GMT
* The webpage says that liquid is collected in the bottom of the unit. How is this liquid handled? What may be done with it?
The Tub has a drain point fitting. The material should be discharged to a sanitary sewer or leach field. It can be discharged directly, held in storage tanks, or pumped to a drain or tank. Some operators do not even generate leachate.--Stephen LaMarca, GMT
The liquid can be drained off with a garden hose attached to the ball valve that comes with the unit. The liquid must be drained into a sanitary sewer.--Greg Howe, GMT
* How do we calculate the optimal mix of food, leaves, and wood?
Moisture or C:N ratio. Based on trial. It can fluctuate greatly and still produce an excellent compost.--Stephen LaMarca, GMT
The tubs should be loaded approximately 2/3 full with wood shavings and then food can be added. Additional bulking agent can be added as the material becomes more dense. The proportion and type of bulking agent to be used will depend on the types, volumes and moisture content of the green materials that are being added.--Greg Howe, GMT
Honestly, I just shoot for 50/50 green to brown by volume to start off. After some experience with your unique materials you will get a more refined ratio. Realize that the food is going to reduce in volume and weight once added due to structure collapse and release of water. Are you actively trying to get rid of (aka divert) woodchips? I'd suggest you fill the tub 15% with wood chips and then load 60% leaves. The Tub is now 75% full. The leaves are fluffy and will go way down after a few weeks. Keep adding food till the compost looks or feels like its getting too moist and then add somemore dry leaves as needed till the tub reaches capacity. --Stephen LaMarca, GMT
* Is it truly possible to run the Earth Tub continuously? What is the emptying interval in this plan?
Yes. I would assume your university would use two or more units in tandem. When the first Tub is full, you fill the second continuously and let the first cook down. When the second reaches capacity (several weeks) the first is emptied and becomes the active bin again. If two Tubs are used together, up to 300 lbs can be fed to a single tub continuously. If using three Tubs, 450 lbs can be fed to the active tub each day.--Stephen LaMarca, GMT
Depending on the amount of green materials being added, a single system can be managed on a continuous basis. If the amount of greens is small (30 to 50 lbs per day), a single system can be used this way. The tub would probably be emptied every 3 or 4 months on this plan. If larger amounts of food are on-hand and several Earth Tubs are being used it is very easy to use the systems on a continuous cycle by filling one unit and moving on to the next, leaving the materials in the first unit to mature.--Greg Howe, GMT
* In all of the info I've gotten from you (video, brochure, etc.) it seemed that the Automated blower system was an integral part of the Earth Tub. Is this extra? If so, how much extra?
The automated blower was an integral part of the system but we have since adapted our aeration system so as to reduce, if not eliminate, the automated controller unit. The controller is most useful in colder climates. For your climate down in Houston I would recommend against the blower controller. The cost is another $200 to $300 for that option. --Greg Howe, GMT
|last updated 2/16/04
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