Bioresource Technology, Vol.48, No.1, 21-24, 1994
NITRITE PLUS NITRATE RECOVERIES IN PIGGERY SLURRY BY DIRECT DISTILLATION AND MODIFIED KJELDAHL METHODS
Aerobically treated slurry may contain nitrite (NO2-N), and nitrate (NO3-N) which are not detected by standard Kjeldahl total nitrogen determinations. The object of this work was to attempt a recovery of total nitrogen, using fresh, untreated slurry dosed with standard sodium nitrite and nitrate solutions. Three pretreatment procedures were undertaken to include NO2-N and NO3-N, by modification of the Kjeldahl method as follows: (a) Devarda's alloy; (b) reduced iron (Fe); (c) potassium permanganate plus reduced iron (KMnO4 + Fe). Each of these was followed by a standard macro-Kjeldahl digestion and distillation. Pretreatment methods (a) and (b) gave reasonable recoveries of NO3-N added to slurry (82% and 89%, respectively), but the effect when compared to method (c) (99% recovery), was not significant. For NO2-N added to slurry there was a significant difference between methods (a) and (b) (49% and 39% recovery), and method (c) (98% recovery). Method (c) is recommended as a global method to cope with the presence of NO2-N or NO3-N in total nitrogen determinations on slurry. Inorganic nitrogen forms (NH4+-N, NO2-N and NO3-N) were measured on the same fresh slurry by a direct distillation recovery, using magnesium oxide plus Devarda's alloy. Recoveries for added forms of nitrogen by this method were greater than 91%.