I need guidance on how to design and setup a two stage digester for anaerobic digestion of food waste on a laboratory.
- I plan to use two 3l glass bottles, the first bottle for the hydrolysis step and the second bottle for acidogenesis, acetogenesis and methanogenesis. The anaerobic digestion will be conducted at a thermophilic temperature of 55°C (submerged in a water bath) and hydraulic retention time of between 10-12 days for the first bottle (hydrolysis) and between 20-25 days for the second bottle (rest of steps).
- The experiment will be conducted under batch conditions. Food waste will be mixed with microbial inoculant and sealed under anaerobic conditions in the first bottle.
My question is how do I transfer the food waste from the first bottle to the second bottle after the hydrolysis step is completed? If I open the first bottle, it won't longer keep anaerobic conditions. I have read some papers in which they use a pump from the 1st reactor to the 2nd reactor, however this experiments are reactors of bigger capacity (+10l), especially designed or used at industrial level.
Appreciate your suggestions.
I've used a peristaltic pump and tubing to transfer the fluids at that scale. The key problem is finding a cap assembly that can be used to attach the tubing. You'll also want to find a way to deliver a makeup volume of Nitrogen so that you won't get an inflow of air when you displace the volume during fluid transfer. Finally, make sure you select an oxygen-impermeable pump tubing to minimize reoxygenation during fluid transport.
Here you can find a couple of photos with the cap assembly we use.
It is made of stainless steel, with three ports (OD 6 mm): for sampling, purge or what ever. This piece was manufactured by a local workshop. The seal is a cheap sealing gasket, used for hot water systems, and purchased in a local plumbing store. It was drilled with a paper sheet puncher to make room for the sampling tubes. I recommend its replacement for each trial. The red plastic cap is from a GL45 glass bottle which was cut off (use a drill and a small hand saw) to allow the sampling tubes to pass through.
I can check but I recall we did pump from first to second and they were ten liters. We had an effluent tank in between.
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