How can I manage a ton-per-month worm composting?

Question

I already have a composting bin in my kitchen, and I'd like to upscale it to my whole building, which has 32 apartments. This is about a hundred people.

I've explained why and how to my neighbors and got a favorable vote so now I can use the common parts of the building to enable worm composting for everyone.

But then I considered the scale of the thing and got scared. At 2kg/day/apartment, that's 2 tons per month... Even if we only get 1kg/day/apartment, and only half my neighbors contribute, I still get an industrial half a ton per month.

Anyway I have two options:

1. Centralize the thing and put one big bin somewhere
2. Put one bin per story, alongside the usual trash bins, each serving 4 apartments (10-15 people)

Either way I don't really know how big the bins/bin stacks should be for such quantities of raw material.

I could not find anything of that scale. Duckduckgoing it gives off either individual-scale solutions, up to 4 people, or industrial, hundreds of thousands of kilos per month, automated things.

I'd be glad to hear from anyone who has done something on a similar scale.

Answer 1

In Australia Wheely Bin Worm Farms are fairly common. They're usually built into a 140 litre wheely bin. We had one with 6 students living in a house but at times struggled to keep it fed because we also had chickens and a composting system. We used to raid the local fruit and vege shop's rubbish bins for extra stuff to feed them, and also used that green waste for general compost in our garden. But it sounds as though you have the opposite problem - too much compostable material.

They're easy to make but the bins are expensive (here ~$AUS100 each). If there is a local user of them it would be worth asking whether you can get some from them as bulk purchase prices tend to be lower. Or look for any kind of large plastic container - I bought a number of 200 litre plastic barrels for ~$AUS15 each (under 10 euro) from a local recycle/reuse merchant (he dealt only in second hand food grade bulk containers). We used them as rainwater barrels, but they would also work as worm farms. Also, the plastic bread trays used to deliver bread are a good source of gratings for the worm farms (ask the local bread factory as they will have a supply of broken ones).

That design would easily scale up to a 220 litre wheely bin, and the advantage is that you can move them easily. You can assemble them and get them started somewhere easy for you, and if people are not using one, or one fails (and gets stinky), you can just wheel it down to the garage and deal with it there. You could also easily swap the bins between high-use and low-use groups of people so they all get about the same level of input.

Another advantage is that by having mobile worm farms that are fairly easy to build you can start with one or two and build more as you need them. That also avoids having to buy worms (fed properly worms will double in number every month or so, and any excess will escape much to the delight of any chickens in the area)

Edit: if you want something that is cheap but takes little to no construction expertise you could use polystyrene vegetable boxes (you can see one between the bins in the top left photo above). At least in Australia vegetables that need to be chilled are often transported in polystyrene boxes that are about 25cm wide, 30cm high and 70cm long. And they have a fitting lid, also polystyrene. Those are often available cheap or free from fruit and vege shops. We used those as worm farms for a while since they're cheap and easy. Just poke some holes in the bottom, add worms and food, cover the top with a layer of newspaper and put the lid on. Cut another one down so it's about 10cm high and put that underneath to catch the liquid that runs through the holes you made. You can stack these two high. The problem is that they're somewhat messy to deal with since they don't have handles and you have to life them up to extract the liquid (take the lid off, put it upside down on a few sheets of paper next to the worm farm, lift the top box off and put it on the lid, put the bottom box on top of that, then use a cup to bail out the liquid).

Answer 2

I can't offer anything by way of vermicomposting advice, but an opinion to consider.

1. You are likely to get greater participation by putting "one bin per story, alongside the usual trash bins, each serving 4 apartments (10-15 people)." The more convenient you make participating, the more people will do so. This option requires minimal change in routine on the part of users, so you should get more material with this strategy. But it's also a more modest upscale per bin, which could be more manageable...perhaps you could recruit one person per floor to update you on the state of the bin each week? Minimize your time/effort spent checking multiple bins.

2. If you centralize the thing, the bin will be a more serious upscale from what you're used to, but you're also likely to get less material overall because it requires greater effort from its users. This may be more manageable logistically and will also show you who in your building is committed to composting by going out of their way to do so...identifying potential allies for a future per-floor management strategy.

Admirable undertaking, best of luck!

Answer 3

Be sure to put easy to read instructions above each bin, detailing what to put in the bins and how to do it. Otherwise, there is no telling what people will be putting in there and you could end up with a putrid mess instead of compost.