BIOLOGICAL AEROBIC TREATMENT OF PIG SLURRY IN FRANCE: NUTRIENTS REMOVAL EFFICIENCY AND SEPARATION PERFORMANCES

Abstract

Four types of biological aerobic treatment units were identified in France: (1) intermittent aeration without anyseparation, (2) intermittent aeration followed by sedimentation of aerated slurry, (3) mechanical separation of raw slurryfollowed by intermittent aeration of the liquid fraction and sedimentation of aerated slurry, and (4) mechanical separationof raw slurry followed by intermittent aeration of the liquid fraction and mechanical separation of the aerated slurry. Amongthe 26 treatment units built in Brittany (June 1999), three were studied for 8 weeks. This monitoring period allowed us toestablish nutrient distribution for nitrogen, phosphorus, copper, and zinc. Between 60% and 70% of the nitrogen was removedin gaseous form. Mechanical separation of the raw slurry (press auger) concentrated 25% to 30% of total phosphorus, 10%of total nitrogen, and 8% to 12% of heavy metals (copper and zinc) into a solid fraction representing 4% to 5% of the rawslurry on a weight basis. Separation of the treated slurry using sedimentation or mechanical separation concentrated phosphorusand heavy metals in the sludge (60% to 90%). This separation could lead to a high content of copper and zinc in thesludge, up to 160 and 340 g ton-1, respectively. Consequently, the use of this product on the farm as organic fertilizer couldlead to an overload with regard to agronomic requirements and export is difficult due to the high copper and zinc contents.The clarified supernatant obtained by separation of the treated slurry could be irrigated with a reduced environmental risk.Concerning the biological reactor, the variation of the volumetric load owing to the variation of raw slurry characteristicswas identified as the main parameter influencing the treatment efficiency.