EFFECTS OF AMMONIA ON ANAEROBIC-DIGESTION OF SIMPLE ORGANIC SUBSTRATES

The effects of ammonia on mesophilic digestion of acetate, propionate, acetate-propionate mixture, and lactate were studied in batch serum bottles. The un-ionized ammonia nitrogen (UAN) affected the acetate-utilizing microorganisms in the acclimated mixed cultures to a greater extent than propionate-utilizing bacteria or other trophic groups. The inhibitory effects were less severe in batch reactors supplemented with sulfate, pointing to an antagonistic action of the sulfate-reducing bacteria. Analysis of the inhibition pattern of methane/biogas production has shown that UAN displayed a moderate half-kill dose in the range of 10 millimole and demonstrated a high sensitivity exponent. The latter suggests potential for a sudden failure response of an anaerobic system subjected to an increasing ammonia concentration in the reactor. © ASCE.