The process chain of an anaerobic biogas digester in an integrated two-level reactor:

Step 1: Slurry is fed into the hydrolysis reactor from the collection container. Here hydrolysis and acidification take place.

Step 2: At regularly timed intervals the reaction product created in step 1 is sent to the methane reactor in the digester.

Step 3: The mid retention period in step 2 lasts about 10-20 days. After this period the organic materials have been reduced almost completely to methane and CO₂.

Step 4: The accumulated substrate is discharged from time to time in small amounts and conveyed to the slurry disposal zone.

Step 5: The biogas resulting from fermentation is discharged from the digester via the gas dome for further recycling.