Enumeration of some microbial groups in thermophilic poultry waste digesters and enrichment of a feather‐degrading culture

Methane‐producing, cellulolytic, feather‐degrading, and total anaerobic microbial populations were enumerated in four laboratory‐scale (l l) thermophilic (50°C) poultry waste digesters over a 40d period. Four different operation conditions were: 5 d retention time (RT), 6% volatile solids (VS); 5 d RT, 3% VS; 10 d RT, 6% VS; and 10 d RT, 3% VS. Laying hen manure was the sole source of substrate and micro‐organisms. At theoretical steady state (day 40) the biogas volumetric rate was near 3.0 l/l digester volume (l/l/d) in all but the 10 d RT, 3% VS digester which was 2 l/l/d. The total viable anaerobic population was > 10 6 cfu/ml digester fluid at the first sampling and stabilized at 10 7 –10 8 cfu/ml between days 20 and 40 in all digesters. Methane‐producing bacteria increased from ≤ 10/ml early in the sampling period to 10 5 /ml at steady state in all but the 5 d RT, 3% VS digester which was highest at 10 7 /ml. Cellulolytic micro‐organisms were low throughout the 40 d, generally less than 10/ml. Feather‐degrading micro‐organisms ranged from near 10 2 –10 5 at steady state and were decreasing in number near day 40 in all but the 10 d RT, 6% VS digester which maintained 10 5 /ml after day 20. A feather‐degrading culture was enriched from this digester and subsequently adapted to grow in a medium with feather as the sole source of carbon. Results of this study provide information regarding potential biological upgrading of poultry waste digesters for increased operational efficiency and potential industrial application of a feather‐hydrolytic micro‐organism.