Effects of Large-Scale Manure Treatment Processes on Pathogen Reduction, Protein Distributions, and Nutrient Concentrations

Abstract

<abstract> Large dairy farms produce equally large quantities of manure that must be managed for effective waste disposal, nutrient utilization, and material recycling of bedding or flush water, all while minimizing risks to surrounding ecosystems. This study evaluated a large dairy farm‘s (approx. 4,000 cows) manure treatment system in terms of solids, nutrients, protein, and pathogen indicator levels. The farm studied was selected because it employed different manure treatment operations, including drum screens, a clarifier, an anaerobic digester, a screw-press, and a dissolved air floatation (DAF) unit. The separation processes studied all generally fractionated the nutrients along with the solids. Among the processes, the greatest separation of solids and nutrients on the study farm was achieved by the clarifier. This study also looked at manure proteins, with the data demonstrating that most of the soluble protein was partitioned from crude protein, which remained in the high solids fraction. Beyond nutrients and solids, total coliforms and were tested as pathogen indicators throughout the treatment system to determine if the separation operations impacted pathogen levels. Results showed a fairly stable pathogen level through the process, with the exception of a significant reduction from anaerobic digestion. Longitudinal data revealed that pathogen indicator densities fluctuated by season in the final holding lagoon, likely influenced by water dilution and temperature. Data from this study should help farmers and agricultural engineers design systems to implement on-farm manure management for targeted economic or environmental goals.