That would be very high for normal digesters, and would seriously lengthen the digestion time; that pressure would inhibit digestion or even halt the process entirely. (The bugs get annoyed and refuse to work.) We used to design around an average of 12.5 inches water column. From http://digester.com/learning/introduction-to-anaerobic-digestion/ Typical pressures range from 4-16 inches of water column (there are 27.7 inches of water column in one psi). Now, back to your regularly schedule propane discussion. Please.