“What would be a good worm farm design to build for classroom use? It needs to be relatively small and have access areas to observe how the worms are composting.” ~ Christina
While I haven’t created one myself, I suspect that it would be relatively easy to build a great educational worm bin.
As you’ve pointed out, a key component of such a system will be some sort of observation area so the kids are able to see what’s really going on inside. The easiest option would simply involve using a fish aquarium. I have made a worm bin using an aquarium and it was certainly fascinating to watch the composting process.
As I discovered however, the major downfall of using an aquarium is the fact that it is very difficult to keep everything aerated inside. Aquariums are of course well sealed systems (in order to prevent water from leaking out) so it is inevitable that conditions will become more and more anaerobic over time as materials are broken down and become compacted.
There are a number of ways you can help to keep things oxygenated however.
For starters, you could create your own artificial aeration system using one or two basic aquarium air pumps and some plastic tubing. Simply poke lots and lots of holes all along the length of the tubing, clamp the end shut (fold it over and tightly constrict with a cable tie), then run the tubing all through the starting materials (bedding + food scraps) as you add them to the aquarium. Attach the tube to your air pump, plug it in and away you go
You also certainly don’t need to use a glass aquarium – in fact, some of the plastic aquariums for kids could be ideal since they are inexpensive and quite small. Perhaps you could buy a number of them and then split the class into groups, each taking a slightly different approach with their own system.
The added advantage of a plastic aquarium is that you can drill small holes in the walls near the bottom (or even on the bottom if you have a tray underneath to catch liquid) to help with air flow.
Something else to keep in mind however, is that aquariums also let in a LOT of light. Worms are very sensitive to light, and prolonged exposure can cause them harm. As such, I would highly recommend keeping a dark sheet over top of each aquarium when not making observations, or storing them in a dark location (like a closet or cupboard).
If your school happens to have a dark room for photography, you might be in for a real treat (assuming you can use the room). Worms are not sensitive to red light, so there is a good chance you could actually observe the worms at work (they will move away from the light in regular classroom).
As easy and (potentially) inexpensive as a small aquarium worm bin would be, you may be hoping to build something with a little more of a ‘wow factor’. If you have some decent carpentry skills or at least know someone who does, the sky is the limit.
I found examples of some fantastic looking systems that should help to provide some inspiration in this department. Both systems are based on the same basic idea – a worm bin with some sort of clear viewing wall, enclosed within a cabinet-like structure. Both look great, but the second system is definitely a little more impressive (it may actually have been purchased).
Here is the nice homemade system:
And the more advanced example:
Hope this helps.