Continuous in-house acidification affecting animal slurry composition

• Continuously acidified animal slurry was compared to normal slurry.
• The majority of the inorganic minerals were dissolved.
• Hydrolysis was accelerated, while the subsequent degradation steps were decelerated.
• Particles were electrostatic aggregated.
• Resulting changes in slurry characteristics will affect the later applications.

The emerging slurry acidification technology affects gaseous emissions, fertiliser value, biogas production and solid–liquid separation; however, maximising the advantages is difficult, as the effect of acidification on the slurry characteristics resulting in those observations remains unclarified. A full-scale study was therefore performed, comparing pig slurry from normal in-house slurry management with pig slurry from housing with daily in-house acidification to pH 5.5. The effect on organic, inorganic and particles was evaluated. Increasing dissolved P, Mg and Ca contents indicated mineral dissolution in acidified slurry. Acceleration of carbohydrate hydrolysis was indicated, while deceleration of microbial acidogenesis, acetogenesis, methanogenesis and sulphate reduction was indicated. The particles were larger following acidification treatment causing a lower viscosity, likely due to acidification-induced aggregation. Overall, the acidified slurry was significantly different from untreated slurry; it had higher conductivity, more dissolved inorganic components, fewer small organic compounds, more large dissolved organic compounds, and larger particles.