Recycling Digested Manure Solids for Dairies

摘要

Dairies, in colder climate areas, have been reluctant to use separated manure solids for bedding cows in free stalls due to cow health concerns. The primary objectives of this research was to process dairy manure through an anaerobic digester followedby a manure solids separator and investigate the effectiveness of the recovered fiber as a dairy bedding material. The secondary objective was to see if phosphorus was partitioned into the solids recovered using the solids- separator.A 700-cow Iowa Dairy (Top Deck Holstein (TDH)) utilizing an existing four year old digester was selected for the project site. A NRCS-CIG grant was obtained to help cost-share the manure solids separator on this farm and perform the research work. Data were collected from fresh and composted digested separated manure solids usage over a ten month period beginning February 2006. Two neighboring farmers used composted digested separated manure solids from the TDH facility for a five month period, and allthree farms bedded stalls about once a week. The separated solids provided a consistent product with dry matter averages of 34% and 40% for fresh and composted solids respectively and increased to 72% when used in the stalls. The 254 mm diameter screw-type separator ran an average of 7.7 hours per day producing 40 m~3 of solids daily. TDH uses 40 tons of this material as bedding out of 66 ton per week produced. TDH averaged 6.0 kg per stall in one barn and 8.9 kg per stall in the second barn with longerstalls, while the other two farms averaged 4.6 kg per stall and 6.4 kg per stall. The manure analysis indicates the separator effluent had 14% less TKN and 25% less P_2O_5 than the digester effluent. The fresh separated solids contained 9.8 lbs TKN, 5.7lbs P as P_2O_5 and 5.3 lbs K as K_2O per ton.With proper digester temperatures, gram negative and streptococcus bacteria counts were reduced three log-scale, while coliform bacteria were reduced to <100 cfu/g. Bacteria counts in fresh solids mirrored digester effluent but were further reduced if the solids were composted and the temperature exceeded 60 deg C. All bacteria levels increased (10~4 -10~6) in stalls during the first 24-hour post bedding and remained at this level throughout the period between bedding applications. Somatic cell counts on all dairies have remained the same or decreased with no associated increases in clinical mastitis while using the separate solids.