Acclimation to extremely high ammonia levels in continuous biomethanation process and the associated microbial community dynamics

- Successful acclimation of methanogenic culture to extreme ammonia levels in CSTR.
- Efficient utilization of a 3rd generation biomass as biomethanation substrate.
- The most abundant bacterium (Shinella spp.) was not affected by the ammonia levels.
- C. ultunense increased significantly its abundance during the acclimation process.
- Methanosarcina spp. was the most abundant methanogen at the highest ammonia levels.

Acclimatized anaerobic communities to high ammonia levels can offer a solution to the ammonia toxicity problem in biogas reactors. In the current study, a stepwise acclimation strategy up to 10 g NH4+-N L−1, was performed in mesophilic (37 ± 1 °C) continuously stirred tank reactors. The reactors were co-digesting (20/80 based on volatile solid) cattle slurry and microalgae, a protein-rich, 3rd generation biomass. Throughout the acclimation period, methane production was stable with more than 95% of the uninhibited yield. Next generation 16S rRNA gene sequencing revealed a dramatic microbiome change throughout the ammonia acclimation process. Clostridium ultunense, a syntrophic acetate oxidizing bacteria, increased significantly alongside with hydrogenotrophic methanogen Methanoculleus spp., indicating strong hydrogenotrophic methanogenic activity at extreme ammonia levels (>7 g NH4+-N L−1). Overall, this study demonstrated for the first time that acclimation of methanogenic communities to extreme ammonia levels in continuous AD process is possible, by developing a specialised acclimation AD microbiome.

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