Response of the reactor performances and bacterial communities to the evolution of sulfide-based mixotrophic denitrification processes from nitrate-type to nitrite-type

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An up-flow biofilm reactor was set up to study the effect of the gradually changing ratio of NO3− to NO2− on the reactor performance, bacterial community and metabolic pathways in the mixotrophic desulfurization-denitrification process. With NO3−/NO2− decreasing, the removal efficiencies of NO3−, NO2− and S2−, and the generating efficiency of S0 increased. The top dominant desulfurization-denitrification genera changed from Rhodobacter (5.6 %) to Thiovirga (11.0 %), and the top dominant Sulfate-Reducing Bacteria changed from Clostridium (1.7 %) to Desulfovibrio (7.2 %). The relative abundance of sulfide oxidation gene sqr, twelve sulfate reduction genes and fifteen denitrification genes had the overall trend towards increasing, but that of sulfur oxidation gene sox decreased. The electron acceptor’s evolution from NO3− to NO2− screened the functional bacteria suitable living in NO2− environment to promote the bioreactor’s optimization. The main degradation pathway of the contaminants was predicted that: NO3− tended to utilize organics to release NO2−, while NO2− tended to utilize S2− and S32− to generate N2; after NO3− was entirely consumed, NO2− began to react with organics, S32− and S0. The results obtained in this work can be used as a practical reference for development, optimization and control of NO2−-type mixotrophic desulfurization-denitrification process.