Gaseous emissions and modification of slurry composition during storage and after field application: Effect of slurry additives and mechanical separation

The aim of the study was to evaluate the impact of slurry treatment by additives (EU200^® (EU200), Bio-buster^® (BB), JASS^® and sulphuric acid (H₂SO₄)) and mechanical separation on the physical-chemical characteristics, gaseous emissions (NH₃, CH₄, CO₂ and N₂O) during anaerobic storage at ∼20 °C (experiment 1) and NH₃ losses after field application (experiment 2). The treatments studied in experiment 1 were: whole slurry (WS), WS+H₂SO₄ to a pH of 6.0, WS+EU200 and WS+BB. Treatments for experiment 2 were: WS, slurry liquid fraction (LF), composted solid fraction (CSF), LFs treated with BB (LFB), JASS^® (LFJ), H₂SO₄ to a pH of 5.5 (LFA) and soil only (control). The results showed an inhibition of the degradation of organic materials (cellulose, hemicellulose, dry matter organic matter and total carbon) in the WS+H₂SO₄ relative to the WS. When compared to the WS, the WS+H₂SO₄ increased electrical conductivity, ammonium (NH₄⁺) and sulphur (S) concentrations whilst reducing slurry pH after storage. The WS+H₂SO₄ reduced NH₃ volatilization by 69% relative to the WS but had no effect on emissions of CH₄, CO₂ and N₂O during storage. Biological additive treatments (WS+EU200 and WS+BB) had no impact on slurry characteristics and gaseous emissions relative to the WS during storage. After field application, the cumulative NH₃ lost in the LF was almost 50% lower than the WS. The losses in the LFA were reduced by 92% relative to the LF. The LFB and LFJ had no impact on NH₃ losses relative to the LF. A significant effect of treatment on NH₄⁺ concentration was found at the top soil layer (0-5 cm) after NH₃ measurements with higher concentrations in the LF treatments relative to the WS. Overall, the use of the above biological additives to decrease pollutant gases and to modify slurry characteristics are questionable. Reducing slurry dry matter through mechanical separation can mitigate NH₃ losses after field application. Slurry acidification can increase the fertilizer value (NH₄⁺ and S) of slurry whilst mitigating the environmental impacts through a decrease in NH₃ losses during storage and after application.