Assessment of ammonia emission mitigation efficiency of established and novel field application techniques for anaerobically digested slurry

Biogas can be produced from anaerobic digestion of animal slurry. In Denmark, recalcitrant biomasses are often added along with slurry, resulting in a high dry matter digestate with a high potential for ammonia emission following field application. A total of 12 field trials were conducted to quantify the effects of two digestate treatments and four application techniques on ammonia emissions after field application. Digestate was treated by low dose acidification and separation and applied by trailing hose, trailing shoe, a novel combination of trailing shoe and harrowing tine, and open slot injection. Emissions were determined with a system of dynamic flux chambers and cavity ring-down spectroscopy. Measured ammonia emissions varied substantially among trials and were clearly related to digestate source. Acidification with 1 kg concentrated sulfuric acid per ton slurry effectively reduced emissions in some cases, but the effect was inconsistent and most likely related to dry matter content of the digestate. There were lower cumulative emissions from the liquid fractions after separation compared to the unseparated digestate in all cases, but the reduction effect varied considerably (33-83%). There was no clear difference between trailing hose and trailing shoe. But the modified trailing shoe with harrowing tine significantly reduced cumulative emissions compared to the trailing shoe only (34-39%). Based on the data, it is not feasible to recommend one universal application approach or treatment strategy for consistently reducing emission under all conditions. Future work should investigate the sources of variation in emission mitigation, to understand when specific measures are effective. • NH 3 emissions after field application are clearly related to digestate source • Trailing hose and trailing shoe application yielded similar NH 3 emission • Trailing shoe with harrowing tine reduced emission compared to band application • No clear reduction in NH 3 emission by acidification with 1 kg H 2 SO 4 t -1 digestate • Emissions from separate liquid fraction was 33-83% lower than unseparated