For the optimisation of the biological intermittent aeration treatment of piggery wastewater, biological processes were investigated using 100L pilot-plant. The results demonstrated that more than 60% of total nitrogen was removed in gaseous form by nitrification followed by denitrification during the anoxic phase. During nitrification, oxidation of ammonium to nitrite was slower than oxidation of nitrite to nitrate leading to nitrite accumulation during aeration phase. Finally, a mathematical model was developed from experimental results to obtain process optimisation and used to predict the characteristics of the treated slurry.