Kinetic and microbial analysis of methane production from dairy wastewater anaerobic digester under ammonia and salinity stresses

Abstract The dynamics of microbial communities during anaerobic digestion at different states of acclimation and inhibitions is key to diagnosing ailments of this process. Previous studies focused primarily on concentrations thresholds for inhibition and adaptation. This study investigated the dynamics of methane (CH4) producing communities subjected to ammonia and salinity stresses during batch anaerobic digestion, of dairy wastewater, in both acclimated and unacclimated conditions. Experimental data was fitted into the ‘Modified Gompertz Model’ and resulting lag phase values related to stress conditions. R2-values ranged between 0.95 and 1.00 suggesting a nearly perfect fit of the model to the observed CH4 production. Irrespective of acclimation conditions, digesters under ammonia stresses produced less CH4 compared to those subjected to salinity stresses. Salinity-acclimated digesters performed similar to salinity-free digesters below 12 g L−1 salinity level. Petrimonas and Clostridium XI were the most dominant (50–61%) bacterial genera in salinity-acclimated digesters, whereas Petrimonas, Clostridium XI, Alkaliflexus, Sedimentibacter, and Clostridium III were the most abundant (69–82%) bacterial genera in salinity-unacclimated digesters. In ammonia-acclimated digesters, Petrimonas, Clostridium XI, and Alkaliflexus were the most dominant (55–68%) genera. Petrimonas, Clostridium XI, Alkaliflexus, Sedimentibacter, Clostridium III, Clostridium XIVa, were the most abundant (74–87%) bacterial genera in TAN-unacclimated digesters. Methanosarcina, Methanobrevibacter and Methanobacterium were most abundant archaea in both salinity (71–99%) and ammonia (87–98%) stressed digesters. The principal component analysis demonstrated bacteria clustering in the acclimated and the unacclimated reactors. No such clustering of archaea was evident in either acclimated or unacclimated reactors.