Influence of temperature and feeding mode on digestion and sanitation efficiency during multiple-stage anaerobic treatment of liquid dairy cattle manure

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This work deals with the evaluation of the performance of a multiple-stage anaerobic digestion process with respect to the degradation of organic matter and the inactivation of pathogenic and indicator organisms in liquid dairy cattle manure. Investigations were performed at bench- and full-scale.
During the three-stage mesophilic-thermophilic-mesophilic anaerobic treatment of liquid manure from cattle receiving a high-fiber diet, a comparably high methane yield of 0.24 m3 per kg of volatile solids was achieved. Given a minimum guaranteed retention time of 4 h at 55°C, the level of fecal coliforms in liquid manure was reduced to below 10 MPN per g fresh matter. The concentration of infectious oocysts of Cryptosporidium parvum was reduced by more than 5 log-units. Increasing the feeding interval from 1 to 4 h had no significant influence on the performance of the system. When the temperature in the first treatment stage was decreased from 38 to 20-25°C, the process stability in the thermophilic reactor was significantly improved while overall the methane yield and the reduction of indicator organisms remained essentially unchanged.
Based on these findings, two-stage thermophilic-mesophilic anaerobic digestion can be approved as a treatment technology for liquid manure to minimize the input of pathogenic and indicator organisms from livestock farming into the environment.