This was done regularly in this study by means of a substrate pump. The total slurry volume was about 680 m3. In the digester, the substrates are heated, and fermentation process takes place. The two end products of this process are biogas and digested substrate. The fresh substrate should be periodically stirred to realize an even temperature in the digester and to improve the metabolism of the bacteria. The AD plant has one identical 2713 m3 (diameter 24 m, walls of height 6 m) double membrane and an upright digester heated to 40 C by stainless steel heating pipes (60.3 2 mm and
pipe length 288 m) positioned on the chamber inner walls.