A process combining anaerobic digestion and anoxic/oxic treatment was developed to treat pig slurry in-order-to partially convert organic matter (OM) into a valuable energy and simultaneously to comply with the environmental constraints as regards to nitrogen removal. However, OM content of digested pig slurry is insufficient to allow a further complete denitrification of the mineral nitrogen content. Hence, four different configurations were designed and evaluated to manage the OM requirements and achieve denitrification. Partial nitrification (PN) of ammonium to nitrite was also applied by regulating oxygen inflow time. Thus, the combined process could remove 38-52% of CODt, 79-88% of CODs, 66-75% of TN and 98-99% of NH(4)(+)N concentrations depending on the slurry characteristics. Anaerobic digestion was able to produce 5.9 Nm(3) of CH(4)/m(slurry added)(3).PN allowed a reduction in the oxygen and OM requirements respectively for nitrification and denitrification. Thus, this process trims-down the energy costs at the farm scale. (C) 2010 Elsevier Ltd. All rights reserved.