In situ ammonia production as a sanitation agent during anaerobic digestion at mesophilic temperature

Aim: To measure the sanitizing effect of mesophilic (37 degrees C) anaerobic digestion in high ammonia concentrations produced in situ.Methods and Results: Indicator organisms and salmonella were transferred to small-scale anaerobic batch cultures and D-values were calculated. Batch cultures were started with material from two biogas processes operating at high (46 mmol l(-1)) and low (1.6 mmol l(-1)) ammonia concentration. D-values were shortened from c. 3 days to < 1 day for the bacteria. MS2 had the same D-value (1.3 days) independent of ammonia concentration whereas Phi X174 and 28B were faster inactivated in the control (1.1 and 7.9 days) than in the high ammonia (8.9 and 39 days) batch cultures.Conclusion: Running biogas processes at high levels of ammonia shortens the time to meet EU regulation concerning reduction of salmonella and enterococci (5 log). Unless a minimum retention time of 2 days, post-treatment digestion is needed to achieve sufficient sanitation in continuous biogas processes.Significance and Impact of the Study: Running mesophilic biogas processes at high ammonia level produces residue with a high fertilizer value. With some stipulations concerning management parameters, such processes provide a method of bacterial sanitation without preceding pasteurization of the incoming organic waste.