Effects of Anaerobic Digestion and Solids Separation on Ammonia Emissions from Stored and Land Applied Dairy Manure

Field and laboratory studies were conducted to evaluate the effects of anaerobic digestion (AD) and solids-liquid separation on emissions during subsequent storage and land application. The lab storage tests were conducted for 21 days with manure samples obtained at the following four points in a full-scale AD system: raw manure (RM) delivery, raw manure supplemented with other substrates (AD influent), AD effluent, and AD effluent after solids-liquid separation (AD liquid effluent). Ammonia fluxes from stored AD effluent declined from 3.95 to 2.02 g m(-2) day(-1). Lower NH3 fluxes, however, were observed from AD liquid effluent (1.1 g m(-2) day(-1)) and AD influent (0.25 g m(-2) day(-1)). Ammonia emissions from full-scale manure storages were similar to those obtained in the lab. Results also indicated significantly lower volatile fatty acid (VFA) in AD effluent and AD liquid effluent compared with that from the AD influent, indicating significant reduction in odor generation potential due to AD and solids-liquid separation processes. Two manure application methods (surface application and manure injection) for both non-AD and AD manures were simulated in the lab and studied for 9 days. Surface-applied non-AD manure exhibited the highest NH3 flux (0.78 gm(-2) day(-1)), while injected AD manure led to the lowest NH3 flux (0.17 g m(-2) day(-1)). Similar NH3 emissions results were observed from the field studies. Overall, while AD of dairy manure resulted in significant increases in NH3 emissions from stored effluent, the AD process significantly reduced NH3 emissions following application of AD manure on land.