I have some background in bioprocess engineering. I love the challenge of this project, because anything doing culture growth requires special solutions.
It has to be sterile (or easy to sterilize), needs temperature control, mixing, and pumps to add substrate and take out culture, and to pump the culture to the sensor station to assess any of the growth parameters. Also you have to consider air exchange, bacteria use up oxygen and produce carbon dioxide. In the industry they use stainless steel for all vessels, heating and cooling systems, huge stirrers, and industrial pumps. I think most of it can be easily replaced in a DIY approach.
My take on it would be the following, please adapt or discard or criticise to your liking. I based it on
- Sturdy plastic container, be it sturdy plastic bags or maybe something like a large tupperware container with ports drilled into it to connect to plumbing/tubes
- silicone tubes to contain the liquid and pump it in or out using a simple peristaltic pump.
- A diy photometer. It is really quite simple, you need a constant light source (best around 600 nm), and a photo detector and by measuring the absorption of the culture you get an estimate of cell density
- A magnetic stirrer. basically a rotating magnet rotates a second magnet that is submerged in the culture. This is simple to build and avoid additional moving connections to the outside world.
- Use only materials that can survive 100 °C (better 120°C) to be capable to heat sterilise your machine. Otherwise you can use chemical sterilisation that is sometimes a bit less efficient.
What you should bring (or get quickly on saturday):
So what you definitely need is someone with plumbing/tube connection experience and basic electronic engineering.
I am not hacking myself this year, but I can give you an aliquot of E. coli for a test run at the end, and if you want to, can give you input on your hack. Also I can maybe bring some sterile filters that you can use to sterilise inflowing air.