Ammonia is a major environmental factor
influencing biomethanation in full-scale anaerobic digesters.
In this study, the effect of different ammonia levels on
methanogenic pathways and methanogenic community
composition of full-scale biogas plants was investigated.
Eight full-scale digesters operating under different ammonia
levels were sampled, and the residual biogas production
was followed in fed-batch reactors. Acetate, labelled in the
methyl group, was used to determine the methanogenic
pathway by following the
14CH
4 and
14CO
2 production.
Fluorescence in situ hybridisation was used to determine
the methanogenic communities’ composition. Results
obtained clearly demonstrated that syntrophic acetate oxidation
coupled with hydrogenotrophic methanogenesis was
the dominant pathway in all digesters with high ammonia
levels (2.8–4.57 g NH
4+-N L
-1), while acetoclastic
methanogenic pathway dominated at low ammonia
(<1.21 g NH
4+-N L
-1). Thermophilic
Methanomicrobiales
spp. and mesophilic
Methanobacteriales
spp. were the
most abundant methanogens at free ammonia concentrations
above 0.44 g NH3-N L
-1 and total ammonia concentrations
above 2.8 g NH
4+-N L
-1, respectively.
Meanwhile, in anaerobic digesters with low ammonia
(<1.21 g NH
4+-N L
-1) and free ammonia (<0.07 g NH3-
N L
-1) levels, mesophilic and thermophilic
Methanosaetaceae
spp. were the most abundant methanogens.