Novel bioaugmentation strategy boosted with biochar to alleviate ammonia toxicity in continuous biomethanation

Highlights

• Ammonia tolerant methanogens stored in gel for long period and used on demand.

• Bioaugmentation boosted with Biochar enhanced the methane yield by 28.6%.

• A biochar and biogel synergism was found to alleviate ammonia inhibition.

• Bioaugmented M. thermophilus sp. contributed largely to rapid methane recovery.

• Biochar addition created a long-term ammonia tolerance of Methanosarcina spp.

Abstract

This study investigated for the first time if ammonia tolerant methanogenic consortia can be stored in gel (biogel) and used in a later time on-demand as bioaugmentation inocula, to efficiently relieve ammonia inhibition in continuous biomethanation systems. Moreover, wood biochar was assessed as a potential enhancer of the novel biogel bioaugmentation process. Three thermophilic (55 °C), continuous stirred-tank reactors (R_Bgel, R_Char and R_Mix), operated at 4.5 g NH₄⁺-N L^-1 were exposed to biogel, biochar and mixture of biogel and biochar, respectively, while a fourth reactor (R_Ctrl) was used as control. The results showed that the methane production yields of R_Mix, R_Char and R_Bgel increased by 28.6%, 20.2% and 10.7%, respectively compared to R_Ctrl. The highest methane yield was achieved by the synergistic interaction between biogel and biochar. Additionally, biogel stimulated a rapid recovery of Methanoculleus thermophilus sp. and syntrophic acetate oxidising bacteria populations.