THE CHEMICAL BUFFER SYSTEM IN RAW AND DIGESTED ANIMAL SLURRY

Slurry pH is of great importance for the regulation of ammonia volatil ization from livestock slurry, and therefore more knowledge of the buf fer system controlling pH is urgently needed for modelling ammonia los ses from stored and surface-applied slurry. The composition of 17 diff erent Danish cattle, pig and biogas plant-digested slurries was studie d. The results were used to describe the main buffer components in the slurries, and to discover the most important chemical components nece ssary for modelling slurry pH. The results showed that the pH of slurr y was mainly controlled by the species NH4+/NH3, CO2/HCO3-/CO3(2-) and CH3COOH/CH3COO-, and that ion pair formation did not change the ionic balance significantly. There were only trace amounts of Ca2+, Mg2+ an d inorganic phosphates in solution due to precipitation of CaCO3 (calc ite) and MgNH4PO4.6H2O (struvite). Measured electrical conductivities were found to be strongly correlated with the calculated ionic strengt h.