Thermophilic and mesophilic operation of an anaerobic treatment of chicken slurry together with organic residual substances

Lab-scale investigations on mesophilic (35 degrees C) and thermophilic (55 degrees C) degradation of a mixed substrate consisting of chicken slurry, organic fraction of municial solid wastes and other co-substrates were carried out. Both the degradation of VSS (volatile suspended solids) and the formation of methane were determined for different raw substrates at several hydraulic retention limes between 4 and 20 d. It could be shown that thermophilic operation was advantageous at fermentation times below 20 d regarding methane formation and degradation of VSS, However, the dewatering of the resulting residues of digestion was more difficult than the dewatering process of the mesophilically digested sludge. Due to the shifting of the NH4-NH3-equilibrium under thermophilic conditions the water recycling was complicated. With regard to peak loads the mesophilic system was more susceptible to disturbances than the thermophilic one. Stable mesophilic operation prooved to be possible at hydraulic retention time beyond 8 d. (C) 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.