Perchlorate and nitrate is a kind of common contaminants in groundwater,however,perchlorate is usually present at low concentration(in ppb range),while nitrate is often found in much higher concentration(in ppm range).It is difficult to develop a remediation technology to remove both perchlorate and nitrate efficiently from contaminated water resources.Biological technology is the most favorable way to remove them.During the sulphur autotrophic bioreduction process,microorganisms utilize elemental sulphur as an electron donor and reduce the two under hypoxic conditions to produce by-products such as sulfate.At present,some conclusions in this area of research are still unclear.The degradation kinetics of two pollutants,the formation of by-products,and the spatial distribution of microbial populations remain to be further clarified.Therefore,the following studies have been conducted in this study on the combined pollution of perchlorate and nitrate in sulphur autotrophic reduction water:1.This study investigates the bio-autotrophic reduction of perchlorate from an aqueous solution in a sulfur packed bed reactor.The reactor was operated with over 99.00%efficiency for 21.00±1.40 mg/L perchlorate removal when the hydraulic retention time(HRT)ranged from 12.00 h to 0.75 h at 27±2°C.The half-order kinetic model fit the experimental data well.The 1/2K1/2vis 7.37 mg1/2/L1/2·h.The reactor was operated with over 97%efficiency for 468.74±6.80μg/L perchlorate removal when the hydraulic retention time(HRT)ranged from 4.00 h to 0.75 h at 27±2°C.The half-order kinetic model fit the experimental data well.The 1/2K1/2vis39.59ug1/2/L1/2·h.The sulfur(S)disproportionation reaction proceeded remarkably at the beginning of the reduction,regardless of the concentration of perchlorate in the influent water,a longer HRT promoted S disproportionation,resulting in excessive sulfate generation and alkalinity consumption.Besides,the spatial distribution of the microbial communities and the dominant bacteria function under different HRTs was analyzed using high-throughput sequencing.The genus Chlorobaculuma was identified as the dominant bacteria associated with S disproportionation.When perchlorate is high concentrations,The Thiobacillus,Thiobacter,Sulfurmonas,Methyloamlis and Sulfuricurvum genera are speculated as the main perchlorate reduction bacteria(PRB).Sulfurimonas is the major PRB when perchlorate is at a low concentration.In addition,the sequencing results showed that with the increase of the reactor height,αdiversity of the microbial community in the reactor showed a downward trend.2.This study investigated the simultaneous removal of perchlorate and nitrate from aqueoussolutioninanup-flowsulfurautotrophicreductionreactor.When22.03±1.07mg-N/Lnitrate coexisted with 21.87±1.03 mg/L perchlorate in the influent,the reactor could be operated at HRT ranging from 12.00 h to 0.75 h,A period of 2-6 days was needed for acclimation while nitrate was more easily to remove.with a removal efficiency exceeding 97%for the two contaminants.Half-order kinetics model fit the experimental data well;this indicatesthat diffusion in the biofilm was the limiting step.The 1/2K1/2v/2v of perchlorate is 6.63 mg1/2/L1/2·h,and the 1/2K1/2v/2v of nitrate is 6.92 mg1/2/L1/2·h.This indicates that Perchlorate reduction required a longer reaction time than the coexisting nitrate.When22.03±1.07mg-N/Lnitrate coexisted with 471.7±50.3μg/L perchlorate in the influent,the reactor could be operated at ahydraulic retention time(HRT)ranging from 4.00 h to 0.75 h,with a removal efficiency exceeding 97%for the two contaminants.Half-order kinetics model fit the experimental data well;The 1/2K1/2v/2v of perchlorate is 26.03 ug1/2/L1/2·h,and the 1/2K1/2v/2v of nitrate is 7.12 mg1/2/L1/2·h.Indicating that even if the coexisting nitrate concentration is 46times that of perchlorate,perchlorate reduction required a longer reaction time than the coexisting nitrate.Sulfur(S)disproportionation was inhibited when nitrate was not completely removed;whereas it was accelerated when perchlorate decreased to low concentrations.This process thereforegenerated excessive sulfate and consumed much more alkalinity.High-throughput sequencing method was used to analyze bacterial community spatial distribution in the reactorunder different operational conditions.The reduction of the two contaminants was accompanied by a decrease in biodiversity.The results indicated that Sulfuricella,SulfuritaleaThiobacillusand Sulfurimonas are effective NB(Nitrate-reducing bacteria)/PRBand their abundance decreases with reactor height.TheFerritrophicumgenus was responsible for nitrate reduction;In addition,the study found that theαdiversity in the reactor was decreasing with the degradation of pollutants. |