This is completely conjecture, so don't take my word for it. But if we assume that a worm will eat half its body weight per day, then 8 pounds of worms should eat 4 pounds of food per day. That would equal 4 pounds of castings.

I don't think you get a pound of castings from a pound of food. Up to 90% of food added is water. Much of that evaporates or drips through. I have read and experienced reduction of 80-90% by volume, but not sure aboit weight.

I will take my best guess here. 4 lbs of castings would be about 1/2 gallon. I would estimate 8 parts by volume in(food) = 1 part out(castings) means you need to feed 3.5 gallons of food per day. If 3.5 gallons of food weighs 8lbs/per gallon, that would equal 28lbs of food per day. If worms eat 1/2 their weight per day, you would need 56 lbs of worms and about 28 sq.' of bin surface area at 2lbs/sq.'.

I know that was a little confusing, and it is my opinion and guess. If you want yo accomplish this, you should consider flow-through systems.

Good luck, Pete

Mendopete, I would think after the worms have digested what they can, that the compost they leave behind would consist of the broken down food, plus its moisture content...the water from the food isn't going to a separate channel/compartment, and my worm bin is never saturated with "worm tea". So any water that's in the food, that the worms leave behind as urine, should be reabsorbed by the composts/castings left behind, and be factored into its weight. I'm assuming...the idea of only 1/8 or 1/9 of the food being left behind as castings seems impossible to me...I hope someone else is able to confirm or maybe add to either of our theories? Please help. Thanks.

Mendopete, are the flow through systems the same as the stackable systems where the worms simply travel their way up through the stackable trays to eat food, while the compost/castings left behind are harvested?

Flow-thru systems are quite different than stackable systems. Flow through refers to food going on top and castings coming out the bottom. Commercial models are available, such as the Worm Wig-Wam or the Worm Inn. Many peo[ple build their own. You basically need a 2'tall box sitting on some sort of grate or grid. This sits on a stand a few feet off the ground. Cover the grate up with paper ar cardboard and start vermicomposting. When it gets 18" deep or more, start to rake castings out of the bottom. Advantages are great airflow, and mostly worm and cocoon-free castings.

I think Mendopete is right about losses of mass due to evaporation. Remember that any bin system must be open to air flow, and as long as the stuff exposed to air is wetter than the air, moisture is gonna move to the air.

Earthworms don't have urinary tracts.

My own observation is that compost is less than half the volume of the stuff composted. But I'm not weighing in and out so I don't have a feel for weights. Since the answer to the ratio of weight in to weight out depends partly on the kind of stuff you're composting, I really don't see any way around trying this out and seeing how it goes.

Re stackable trays, which I have, see various threads (via search) on the difficulty of teaching this system to the worms. On the whole, more worms will be toward the top where the feeding happens than the bottom, but some will always be hanging out down at the bottom. It's not as neat as the people who sell stackable trays would have you believe.

To get 4 pounds of castings a day everyday, wow, that kinda hurts to think about. It also depends on how wet or dry your system is. Mine flow thru systems tend to be dry and I tend to think about volume rather than weight.

I don't know if any single common commercial system is capable of that. The only system I can think about for this scale is a Oregon Soil Corporation Reactor (OSCR).

Really my first question is what is your food source to support this? I'd think either you had livestock or a restaurant unless you were buying worm food.

Along with Mr_Yan I too "I tend to think about volume rather than weight". Vermicompost could be a gallon of water with one vermi poop or a lot of vermipoop dehydrated to zero water. There is no standard amount of moisture for vermicompost that I am aware of. The vermipoop itself can be 100% only poop or have quite alot of unvermied material still in it. There is no standard for this either that I am aware of.

Nobody ever really talks about a number of worms producing a set amount of vermicompost. Usually they just build a system and make it larger if they need more vermicompost. The worms regulate to the size of the system, the temperature and the amount of food. A set number of worms to produce a set amount of vermicompost sounds logical until one grabs a rake and starts looking around a compost bin.

http://www.organicagcentre.ca/docs/vermiculture_farmersmanual_gm.pdf

has some more discussion of input/output ratios. In particular:

"In general, outputs from vermicomposting processes can vary from about 10% to closer to 50% of the original weight of the inputs."

Some mass is also apparently lost as CO2.

There's discussion of worm mass and flow rates on page 25 of this: http://www.wormresearchcentre.co.uk/scientific/Vermicomposting%20Evaluation.pdf

But remember this is for intensively-managed commercial operations with inputs easier for worms to eat.

Thank you Colin, that was really helpful.

If you find out the answer please let us know.

Also one does not necessarily purchase that many worms but purchases less and regulates the system up to that many.