Nitrification limitation in animal slurries at high temperatures

Nitrification rates in two types of animal slurry were measured at temperatures between 20 and 60°C. The rates were assessed in rapid laboratory assays using samples from aeration tanks of large-scale treatment plants for pig or veal-calf slurry. Maximum nitrification rates for the two slurries were observed around 35 and 40°C. For veal-calf slurry, the observed maximum rate was 1.5 mmol NH+4 per gram volatile suspended solids per hour. The maximum rate for digested pig slurry was 0.11 mmol g−1h−1). For digested pig slurry, a sharp drop in nitrification rate was observed at temperatures higher than 40°C. The rate in veal-calf slurry dropped at temperatures higher than 45°C. No nitrification was observed above 45°C in digested pig slurry and above 50°C in veal-calf slurry.