Distribution of nitrogen in liquid and solid fraction of pig and dairy manure in anaerobic digestion reactor

It is important to understand the forms and distribution characteristics of nitrogen during the anaerobic digestion of animal manure slurry, which would provide theoretical principle and precondition for the treatment and utilization of digested slurry and solid residue. The objective of the study was to analyze the distribution of nitrogen in liquid and solid fraction in digested pig and dairy manure using the continuous stirred tank reactor (CSTR) at condition of medium temperature (37±2)℃. Results showed that the nitrogen loss rates were 12.2% and 11.5% in bioreactors digested with pig and dairy manure slurries, respectively. The percentages of nitrogen content in total solid fraction of digested pig manure and dairy slurries and residues remained in reactors were 61.9% and 72.7%, respectively at the end of experiment. The nitrogen content in liquid fraction of digested pig manure increased by 10.7% and decreased by 28.0% in solid fraction. However, the nitrogen content in liquid fraction of digested pig manure decreased by 8.7% and only increased by 2.8% in solid fraction. The increase rate of NH4+-N reached to 162.2% and 90.0%, respectively after the digestion of pig and dairy manure, which were 43.3% and 30.5% of total nitrogen. The NO3--N content was decreased by about 50.0% and 45.2%, respectively after the digestion of pig and dairy manure, which were less than 1% of total nitrogen. The dry weight in solid residue of pig manure was significantly higher than that in dairy manure, so regular residue handling was needed during the anaerobic digestion of pig manure compared to dairy manure.