중온 혐기성소화 시 암모니아 독성 저해

Ammonia Inhibition on Mesophilic Anaerobic Digestion

This study evaluated acute toxicity of ammonia in mesophilic anaerobic digestion of synthetic wastewater and thermally hydrolyzed waste sludge. The inhibition effects of ammonia, in terms of total ammonia nitrogen (TAN), under various pH values on mesophilic anaerobic microorganisms were investigated. Anaerobic batch feeding reactor (ABFR) operated at a chemical oxygen demand (COD) of 3.85, 7.5 and 15.0 g/L were subjected to free ammonia (FA) concentrations of 97.1, 225.5 and 362.4 mg/L. The reactor operations presented a case of chronic inhibition and it was observed that FA concentrations of 360 mg/L caused a drop in methane yield by as much as 60% with respect to FA concentrations of 97.1 mg/L. Batch anaerobic toxicity assays (ATA) were also performed to evaluate the acute toxicity effects of TAN and pH on anaerobic digestion at mesophilic condition. Modeling based on the results of ATA indicated that except parameter m, model parameter values (I*,Rm,and n) decreased with the increase of TAN concentration and the highest SMA for a given TAN level was observed over a pH range of pH 7.6-8.5. TAN concentration causing 70% inhibition occurred in the over 3.0 g/L in mesophilic anaerobic digestion. Results of bacterial community analyses, Chloroflexi and Synergistetes were the dominant communities at TAN less than 3.0 g/L and Firmicutes was the dominant community at TAN higher than 3.0 g/L. Even though the Phylum of Firmicutes dominated the gas production in anaerobic digestion at TAN concentration of above 3.0 g/L decreased due to the decrease of the Phylum of Chloroflexi and Synergistetes by high TAN concentration.