Nutrient recoveries from plug-flow anaerobic digestion of poultry manure

Anaerobic digestion provides for the production of a biogas fuel while concurrently conserving the nutrient value of manures used. The nutrients placed in anaerobic digesters are, however, subject to possible transformations. The objectives of this study were to evaluate changes in the N composition following plug-flow digestion of poultry manure, and to determine the distribution of N, K, P, Ca and Mg between the outflowing effluent and the settled manure sludge which remained in the digester. Total Kjeldhal N (TKN) was completely recovered in the pilot-scale digestion operated with 6% influent TS, 35°C and 30 day retention time. Mineralization of poultry manure organic N by the digestion process was 53%. Consequently, NH₄⁺-N in the digested manure accounted for the large majority (79·6%) of the TKN. The effluent accounted for the majority of the N and K present in the digested manure (91·2 and 95·9%, respectively). The settled manure sludge, accounted for 26·3% of the recovered TS and contained approximately 30% of the P, Ca and Mg.