Simultaneous Removal Of Sulfate And Nitrite In Integrated Desulfurization Denitrification Process

The rapid development of Chinese economy is closely related to more and more industrial activities,during which,chemical,pharmaceutical and leather factories will produce large quantities of wastewater containing organic matters,sulfate,nitrate and nitrite,which needs to be properly treated before discharged.At present,the main choice for the treatment of organic wastewater containing sulfur and nitrogen remains to be subsection process or series process,due to less research on the integrated removal process.In this thesis,the simultaneous removal of sulfate(SO42-),nitrite(NO2-)and organic carbon in an anaerobic up-flow reactor was investigated.First,the effects of HRT,different carbon sources and organic carbon concentration on the process performance were analyzed with a combined macrocosm and microcosm method.The application of high throughput sequencing method was used to investigate the microbial community structure at different locations in the reaction system,so as to clarify the reaction pathway of SO42-and NO2-in the reaction system and the interaction mechanism between the microbes.Secondly,batch experiments were carried out by inoculating activated sludge containing sulfate-reducing bacteria and denitrifying bacteria,to investigate the interaction mechanism between these two bacteria under different environmental conditions,such as S/N,organic carbon concentration,sulfide(S2-)concentration,ammonia nitrogen(NH4+)concentration,ferrous ion(Fe2+)concentration and salinity.The main results were drawn as follows:(1)The simultaneous removal of SO42-,NO2-and organic carbon in the integrated process of simultaneous removal of sulfate and nitrite reached 73.7%,99.6%and 95.0%,respectively.Besides,S2-formed in sulfate reduction process was further incompletely oxidized to elemental sulfur(S0),with the yield of S0 reaching over 90%.The NO2-was reduced to nitrogen,and organic carbon was converted to carbon dioxide.The analysis of the microbial community structure at different positions in the reactor showed that Desulfomicrobium and Desulfovibrio served as the dominant functional bacteria in the lower part of the reactor,where the sulfate reduction reaction mainly occurred;Sulfurovum was the dominant functional bacteria in the central part of the reactor where autotrophic desulfurization was the main denitrification;Alcaligenes and Sulfurospirillum were the dominant functional bacteria in the upper part of the reactor where heterotrophic denitrification and elemental sulfur reduction reaction occurred.The presence of elemental sulfur reduction confirmed that a large amount of S0 was produced in the upper part of the reactor.In addition,heterotrophic denitrification and organics degrading bacteria were found in all parts of the reactor,indicating that heterotrophic denitrification and organic carbon oxidation reaction existed in all parts of the reactor.(2)Both sulfate reduction and heterotrophic denitrification were inhibited at low S/N values.However,the reaction rate of denitrification was inhibited and NO2-was completely removed after 60 h,while the removal rate of SO42-was lower than 42.28%for the sulfate reduction.With high organic carbon concentration,the competition between sulfate reduction and heterotrophic denitrification was weakened,which increased the removal efficiencies of SO42-and NO2-to 82.46%and 100%,respectively.S2-inhibited sulfate reduction at the concentration of 25 mgS/L,with no effect on heterotrophic denitrification.To increase the concentration of NH4+ and Fe2+ to the appropriate level(NH4+=20 mgN/L and Fe2+=20 mg/L)could facilitate sulfate reduction and heterotrophic,denitrification,and the removal efficiencies of SO42-were the highest at 87.63%and 87.49%,respectively,while the removal efficiency of NO2-reached 100%within 24 hours.Salinity had a great inhibitory effect on sulfate reduction,with the SO42-removal efficiency of only 46.22%at 30 g/L salinity,indicating that sulfate-reducing bacteria could not adapt to high salinity environment.However,the employment of seawater enhanced the sulfate reduction reaction,because a lot of major elements and halophilic sulfate-reducing bacteria in seawater could promote the sulfate reduction reaction.All the different salinity conditions had no effect on denitrification,indicating that heterotrophic denitrifiers were more adaptable to high salinity environments.To sum up,the interaction between sulfate-reducing bacteria and heterotrophic denitrifiers was shown as follows:1)both of them competed for organic substrate;2)NO2-could inhibit sulfate-reducing bacteria,so the concentration of NO2-should be decreased to weaken the inhibition of heterotrophic denitrification and NO2-on sulfate-reducing bacteria;3)salt tolerance of sulfate-reducing bacteria was much lower than that of denitrifying bacteria;4)desulfurization denitrifying bacteria existed and could further oxidized S2-to SO42-.Therefore,the key factor to the stable operation of this integrated process is to reduce the strength of heterotrophic denitrification to improve the competitive ability of sulfate-reducing bacteria,and to enhance the degradation efficiency of SO42-from the source,so that SO42-can be converted to S2-,which can promote the reaction strength of autotrophic desulfurization and denitrification.