Field measurements of ammonia (NH3), nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) were carried out from biological aerobic treatment plants installed in Brittany (Western France). Three biological aerobic reactors and four treatment by-product storages were studied. The field results showed that the emissions of CH4, CO2 and NH3 were more important for the non-aerated effluents (raw slurry and separated solid fraction), which have higher ammonium and organic matter levels than treatment by-products. N2O was only detected from biological reactor and was lower than 1% of total nitrogen entering treatment plant. The assessment and calculation of annual gaseous flux based on these field results and an estimation of raw slurry, matter flows and gaseous emissions for each module of the treatment was done for 4 slurry management schemes for a farrowing-fattening farm with 200 sows. In all cases, the environmental assessment shows a decrease of the greenhouse gases and NH3 by using a biological treatment compared to a traditional manure management based on 6 months storage before spreading. The reduction is 30-50% to 68 % of NH3 when the plant is or not set up with a mechanical separation device. Greenhouse gases are reduced by about 55% whatever the biological treatment plant.