Biodigester Log

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See Biodigester for working page.

Wed Mar 14, 2018

A second test of draining water into the digester revealed that opening the gas valve did not fix the backflow issue. It turned out to be syphoning after all: after closing the inlet valve, we could hear it sucking air as water backflowed into the sink.

Marcin installed a one-way valve under the sink. This appeared to work sometimes, but not all the time. We decided to break the syphoning, rather than just relying on the valve, by connecting the inlet pipe to the stack vent.

Tue Mar 13, 2018

Marcin connected kitchen sink to the biodigester on the evening of March 12, 2018. At this stage, Marcin hadn't yet installed the one-way valve under the kitchen sink and had closed off the gas outlet on the bio-digester. The next day Catarina, unaware of how the connections been made, used the kitchen sink. Log of messages:

C: I did the dishes, drained the water and all seemed to go well. Then I came to the computer to congratulate you on a good job. But when I next looked at the sink a few minutes later, it was full of dirty water. It seems water is backing up into the sink. Is this the water that is supposed to remain in the pipes and kept in check by the one-way valve? Or could it be an issue with the level of the sink in relationship to the level of the overflow?

I'm trying to trace the source of the issue, but it's puzzling.

At first I thought it was the water left at the top of the vertical length of pipe that was backing up into the sink, which is at a lower level. But if that was the case, why wouldn't this have happened before it was hooked up to the digester? It would make much more sense if it had been so. So I can neither understand why it didn't happen before nor why it's happening now. My best guess is that it's either syphoning or there is some pressure from the digester that is sending water back into the sink.

More details:

- At first the water backflows into the sink quite fast. This must be just gravity: water at the top of the vertical pipe is just flowing down into the sink which is lower. Though I still don't get why this didn't happen before. - Once the water reaches the bottom of the sink it slows down considerably. I imagine that gravity is giving it the initial push and then the rest is syphoning.

Some useful videos:

M: I closed off the gas outlet on the biodigester. When you pump water into it, it's like filling an already full balloon—it sends the water back. To temporarily address this, you can open the window, then open the gas valve, then pump out the water from sink.

Catarina did this and no more water backed up into the sink.

C: I'm still don't fully understand what happened. I get that the gas valve was closed, so there is was no room to replace gas/air with water. But what about the overflow drain? Shouldn't that have taken care of it? Or was it that the kitchen line was the path of least resistance?

M: Apparently the way the 2" overflow pipe works, it was easier for the pressure to release over the thinner 1" pipe, which may have acted as a siphon. The 2" is 18" below water, so overflow is facing 18" of effective head.

Tue Oct 18, 2016

"Anything but human shit in a 1/4" insinkerator will soon see it burnt out and blades so dulled it's useless- 1 hp on grass and garbage digester appears to work well." Look into a septic shredder pump as it will slurry anything and pump shit from a reservoir up to a digester no sweat - macerator lift pumps.

Sun Oct 16, 2016

  • Sent inquiry to [1] for 3 cu m biogas bag
  • Janice is a good contact, Solar Cities - and 610-745-4403 for Global Vertical Farms - [2]
  • Contacted -
  • Contacted Dan on biodigester review on 3 cu m system.