Chapter X (In: Progress in Slow Sand and Alternative Biofiltration Processes Further Developments and Applications» (ISBN : 9781780406374, IWA, 2014). Biofiltration of pig manure: behavior of nitrogen compounds P. Lessard*, G. Aubry*, Y. Gilbert*, Y. LeBihan**, G. Buelna** * Département de génie civil et de génie des eaux, Pavillon Pouliot, Université Laval, Québec, Canada, G1V 0A6 ** Centre de recherche industrielle du Québec, 333, rue Franquet, Québec, Canada, G1P 4C7 ABSTRACT Biofiltration using organic media has long been studied. Even so, no thorough studies looking at inside the process have been made. Three pilot-scale organic media biofilters were operated for 450 days to treat pig manure having different COD/N ratios (approximately 5, 9, 15). Air and liquid sampling was done both on influent and effluent but also at different heights along the biofilter. Satisfactory carbon oxidation and nitrification performances were observed, with chemical oxygen demand (COD) and ammonia (NH 4 + ) removals consistently reaching 95%. From 78 to 88% of total nitrogen removal was achieved, meaning denitrification also occurred although the systems were aerated. Nitrate concentration and N 2 O emission were related to the nitrogen content in influent more than with the COD/N ratio. All treatment processes occurred mainly in the top 30 cm of the 190 cm biofilters. Keywords Carbon and nitrogen removal; C/N ratio; denitrification; nitrification; pig manure; trickling biofilters. INTRODUCTION In Quebec (Canada), pig production has increased from one million to more than 7 million pigs per year over the last 30 years. Consequently, pig manure handling has become a problem as land available for spreading is insufficient. In areas where pig production is very important, on site manure treatment can be a solution in order to reduce water pollution problems linked with pig manure. Different processes have been proposed and biofilters using organic media have been proven to be efficient for organic matter and nitrogen removal (Buelna et al., 2008). In fact, biological filters (BFs) using organic material as media have been found efficient for the treatment of domestic and municipal effluents (Lens et al. 1994, Talbot et al. 1996, Roberge et al. 1999) and different types of leachates (Lafrance et al. 1996, Chian and DeWalle, 1996). However, even though