Effect of Anaerobic Digestion of Dairy Manure on Bacterial Survival after Land Application

Abstract

Bacteria survival in dairy manure was evaluated as affected by anaerobic digestion (AD) and method of land application. The AD effluent (AD Ef - after liquid–solids separation post AD) resulted from the anaerobic digestion of dairy manure (80% of total input) and varying feedstocks (whey, egg byproduct, fish stick byproduct, ruminany blood, biodiesel byproduct, fat-grease byproduct, and wood pulp fiber). Anaerobic digestion reduced the number of generic E. coli by 99% and enterococcus by 86%. Two forms of manure (AD Ef and raw manure (non-AD)) were applied to grass plots in 2009 to determine the survival of (GEC) and fecal coliforms (FC) on soil post application. The two forms of manure were also applied by two methods, broadcast and subsurface deposition. The log10 counts/100gms of manure averaged: AD Ef – FC 5.8, and GEC 5.0: non-AD - FC 6.9, and GEC 6.6. Log10 counts of GEC and FC per 100 gm soil increased by 1.5 to 2.5 log10 units within two days on soil that had received non-AD manure. Log10 counts of GEC and FC per 100 gm soil increased by 1.0 log10 units within two days on soil that had received AD Ef manure. Log10 counts of GEC and FC per 100 gm soil declined to background levels on soils within 15 -20 days after AD Ef application, where non-AD manure only reached background levels within 20 days on one of six occasions. Results indicate that AD manure will result in a lower manure derived bacteria population on soil for many weeks post application.