Development of combined acidification and separation of slurry: effect on slurry fractions composition and gaseous emission

Doutoramento em Engenharia do Ambiente - Instituto Superior de Agronomia - UL

Acidification of slurry is used to reduce NH3 emissions and mechanical separation facilities the management of slurry on farms. Acidification and mechanical separation are currently implemented independently at the farm scale in different European countries. However there are drawbacks associated to the current acidification treatment, and it is unknown how acidification before separation affects slurry characteristics and gaseous emissions. This thesis presents an in-depth investigation of the combined acidification and separation of slurry by analyzing the composition of the fractions obtained and the impact on gaseous emissions during storage. Systematic studies for acidification were performed using different additives, target pH values and approaches and different techniques were used to separate different types of slurries. The effects of acidification on slurries dry matter, organic matter and nutrient (N and P) content and their soluble forms were studied and gaseous emissions were followed during storage. The effects of acidification on slurry particle size, nutrient distribution among particles and on separation efficiency were studied. In the acidification experiments, alum emerged as a highly efficient additive for reducing NH3 emissions. The nutrient composition and potential of N mineralization of acidified slurry fractions differed depending on the separation technique used. Acidification affected differently the particle size in slurries, the nutrient distribution among particles and the separation efficiency depending on the additive used. The use of alum promoted an increase of the solid fraction and an almost complete removal of P (90%) to the solid fraction. According to our results, combined acidification and separation improves slurry management: It increases the amount of solid fractions, preserves N in slurries by reducing NH3 emissions during separation, increases the P separation efficiency to the solid fraction, and reduces the total NH3 and GHG emissions during storage. Therefore, the combined technology provides farmers with an economically sound and environmentally safe approach to slurry re-use