Integrated sulfur- and iron-based autotrophic denitrification process and microbial profiling in an anoxic...

The integrated sulfur- and Fe⁰-based autotrophic denitrification process in an anoxic fluidized-bed membrane bioreactor (AnFB-MBR) was developed for the nitrate-contaminated water treatment in order to control sulfate generation and avoid alkalinity supplement. The nitrate removal rate of the AnFB-MBR reached 1.22 g NO₃^--N L^-1d^-1 with NO₃^--N ranging 40-200 mg L^-1 at hydraulic retention times of 1.0-5.0 h. The denitrification in the integrated system was simultaneously carried out by sulfur- and Fe⁰-oxidizing autotrophic denitrifiers. The effluent sulfate generation was decreased by 29.3-70.3% and 31.2-50.9% due to the functional role of Fe⁰-based denitrification in the integrated system. Alkalinity produced by Fe⁰-oxidizing autotrophic denitrification could compensate for the alkalinity consumption by sulfur-based autotrophic denitrification. The sulfur- and Fe⁰-oxidizing autotrophic denitrifying bacterial consortium was composed mainly of bacteria from Thiobacillus, Sulfurimonas, and Geothrix genera. The integrated modes leads to a harmonious co-existence of sulfur- and Fe⁰-oxidizing denitrifying microbes, which may make a difference to the functional performance of the bioreactor. Overall, the integrated sulfur- and Fe⁰-based autotrophic denitrification could overcome the shortcomings of excess sulfate generation and external alkalinity supplementation compared to the sole sulfur-based autotrophic denitrification, indicating further potential for the technology in practice.