Impact of surface acidification of manure on ammonia emission in animal housing

Ammonia is a key substance in the formation of haze precursors, and livestock pen is one of the main sources of ammonia emission. Here, we selected fresh cow and sow manure to evaluate the impacts of surface acidification on ammonia emission under simulated livestock pen conditions with different acids of different concentrations. Acid solution was sprayed on the surface of the manure to acidify the manure surface. Ammonia emission was measured using the dynamic boric acid trap method. Our results revealed that when lactic acid was diluted to 0.012 mol·L^-1 and 0.006 mol·L^-1 and applied on the surface of manure at the rate of 0.31 mL·cm^-2, ammonia emission from sow manure reduced respectively by 43% (P < 0.05) and 32% (P=0.07) in 24 h, compared with the control treatment. Ammonia emission reduced by 74% (P < 0.01) and 61% (P < 0.05) respectively for 0.017 mol·L^-1 and 0.009 mol·L^-1 of diluted phosphoric acids. Ammonia emission of sow manure reduced by 64% (P < 0.01) within 72 h treatment of 0.017 mol·L^-1 phosphoric acid. Using the same treatment method as before, surface acidification of cow manure reduced ammonia emission by 80% compared with control treatment. The frequency of acid addition to manure surface had no significant impact on ammonia emission mitigation when manure was not refreshed. Surface acidification lowered manure pH, but with no significant impact on the whole manure. Overall, surface acidification reduced ammonia emission in animal pens. The reduction efficiency depended not only on the type and concentration of acid, but also on the type of manure. Surface acidification of manure was a cost-effective ammonia abatement technique. This study also supported the increasing understanding of manure acidification technology aimed at reducing ammonia emission from animal pens.