S-Fe Oxidizing Autotrophic Denitrification For Nitrate Removal From Water

Nitrate contamination in water is widespread and the trend is being accelerated. nitrate-contaminateddrinking water easily leads to methemoglobinemia and "blue baby syndrome". The converted nitrosoamino and nitrosoamide are carcinogenic, teratogenic and mutagenic. The nitrate pollution of surface water also leads to the eutrophication, whichdeteriorates water quality and ecological environment. So the treatment of nitrate pollution in water is urgent. Biological denitrification is considered to be one of the most effective ways to remove nitrate pollution from water compared with other physical and chemical methods. Compared to other processes, sulfur-based autotrophic denitrificationhas several advantages such as high efficiency and low cost. But its main disadvantages are sulfate generation and alkalinity consumptionin practice. Based on the processes and pricinples of sulfur-and iron-based autotrophic denitrification, the combined sulfur- and iron-oxidizing denitrification was proposed. In order to improve the nitrate removal efficiency, afluidized bed membrane bioreactor was established which integrated the advantages of fluidized bed and membrane bioreactor.In this work, the mechanism and influencing factors of sulfur and iron synergistic denitrification were studied;afluidized bed membrane bioreactor was established and denitrification performance of nitrate removal in long-term operation was investigated;Themicrobial population structure related to the process was analyzed using high-throughput sequencing.Experimental results were as follows:Under the condition of different S/Fe ratio, the amounts of sulfate couldbe reduced by 25%-62% than thosed generated by the sulfur autotrophic denitrification process.The component analysis the final products in gas and liquid showed thecombining autotrophic denitrification could completely reduce nitrate to nitrogen. The sulfur-based autotrophic denitrificationwas significantly inhibited when the pH was less than 6.The combing iron and sulfur autotrophic denitrification system could reduce nitrate efficiently under the pH of 5-7.The synergistic iron and sulfur-oxidizing autotrophic denitrification membrane reactor was established.During the whole operation,nitrite accumulationwas not detected.Thehighest nitrate removal rate was1.22 gNO₃^--N·L^-1·d^-1, which is 2.7-6.1 times higher thanthat of of the traditionalpacked bed.Alkalinity produced by iron autotrophic denitrification could compensate for the alkalinity consumption bysulfur autotrophic denitrification. The effluent pH maintained at 7.0-7.5when the influent pH is in the range of 7.5-8.0.The membrane module was operate continuously for 20 days without any chemical cleaning, and successful membrane cleaning was practiced very 20-day operation.Quantitative real-time PCR （RT-PCR） and 454 pyrosequencing were used to moditor the biomass and community structure in the combining iron-and sulfur-oxidizingautotrophic denitrifying membrane reactor. The amounts of thearchaea and bacteria increased continuously with the increase nitrate in the influent during the operation.Thiobacillus was the dominant bacteriawhich accounted for 50% of total bacteriaat the genus level.Sulfurimonasas the second dominant bacteria accountedfor about 20% of the bacteria. The content of Geobacter gradually reduced with the operation. At the Phylumlevel the dominant bacteria was Proteobacteria which accounted for 75% of total bacteria.Acidobacteria and Firmicuteswere also the dominant phylum. At the class level, the biggest dominant bacteria belonged to Betaproteobacteria, which varied in the range of 30%-75%.