Western France, is identified as one of the major centres of animal production in Europe. Animal effluents are an important source of fertilizers but are also potential water, air and soil pollutants. Nitrate pollution is of particular concern in France. In this context, several treatment strategies for livestock effluents have been defined and recommended in order to prevent water pollution. For pig slurry, biological aerobic treatment is becoming a common practice. Different types of farm scale units based on aeration have been developed. A survey including collection of technical data of all operating units were conducted with the manufacturers and/or farmers. The study of these data led to the identification of four major types of units design which were subsequently monitored. Three types of treatment farm units were evaluated during a two month period as regards carbon and nitrogen removal efficiency and quality of co-products generated by treatment (C, N, P, K, Cu, Zn). Total nitrogen removal up to 60-70% of the initial total nitrogen content of the raw slurry was observed. Concurrently, removal of total and soluble COD of 49% and 90%, respectively, was obtained. Although liquid effluent represented the more important co-product on a weigh basis (85% of the initial mass), a large part of the "non-biodegradable" elements was accumulated in the sludge which represented only 10% of the initial mass. On average, 70-80% of the total Cu and Zn and 60-70% of total phosphorus were located in the sludge phase. The accumulation of these compounds in the sludge led to high concentration of Cu, Zn and phosphorus up to 140g/tonne, 340 g/tonne and 6.6 kgP/tonne, respectively. According to these results, the management of the sludge phase seems to be difficult without exportation out of the farm.