Mesophilic-thermophilic-mesophilic anaerobic digestion of liquid dairy cattle manure.
The potential of a mesophilic-thermophilic-mesophilic anaerobic digestion system was investigated with respect to improvement of both digestion and sanitation efficiencies during treatment of liquid cattle manure. The pilot plant produced a high methane yield from liquid dairy cattle manure of 0.24 m3 (kg VSfed)(-1) Considering the low system loading rate of 1.4-1.5 kg VS (m3 d)(-1), digestion efficiency compared to conventional processes did not appear improved. The minimum guaranteed retention time in the tubular thermophilic reactor was increased compared to a continuously stirred tank reactor. Levels of intestinal enterococci in raw liquid manure as determined with cultivation methods were reduced by 2.5 -3 log units to a level of around 10(2) cfu/mL. This sanitizing effect was achieved both during mesophilic-thermophilic-mesophilic and thermophilic-mesophilic treatment, provided the thermophilic digester was operated at 53-55 degrees C. A change in feeding interval from 1 h to 4 h did not significantly alter methane yield and sanitation efficiency. It was proposed that a two-stage, thermophilic-mesophilic anaerobic digestion system would be able to achieve the same sanitizing effect and equal or better digestion efficiency at lower costs.
Effenberger
M
M
Bavarian State Research Center for Agriculture, Institute of Agricultural Engineering, Farm Buildings and Environmental Technology, Voettinger Str. 36, 85354 Freising, Germany.
Bachmaier
J
J
Garcés
G
G
Gronauer
A
A
Wilderer
P A
PA
Lebuhn
M
M
D000818:Animals; D001421:Bacteria, Anaerobic / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002417:Cattle; D004755:Enterobacteriaceae / Q000302:isolation & purification; D007700:Kinetics; D008372:Manure / Q000382:microbiology*; D008697:Methane / Q000096:biosynthesis; D012498:Sanitary Engineering; D014865:Waste Disposal, Fluid / Q000191:economics / Q000379:methods*
D008372:Manure; D008697:Methane