Study On The Nitrogen And Sulfide Removal Performance Of Partial Sulfide Autotrophic Denitrification Coupled With Anammox Process

In addition to the serious nitrogen pollution in food processing,oil refining and other industrial wastewater,there is also a certain amount of sulfide pollution,so it is very urgent to explore the simultaneous removal process of nitrogen and sulfide.Anammox process is considered to be one of the most economical denitrification technologies in wastewater.However,this process requires nitrite as a substrate.On the basis of the partial sulfide autotrophic denitrification（PSAD）process,which takes sulfide as electron donor and nitrate as electron acceptor,if the process is properly regulated,when the reaction products are controlled at nitrite（NO₂^--N）and biological sulfur（S⁰）stage,not only can the source of electron acceptor be provided for Anammox process,but also the S⁰ can be recovered and utilized to realize simultaneous denitrification and sulfur removal.Accordingly,this study first explored the effects of different sludge sources on the start-up effect and pollutant removal effect of partial sulfide autotrophic denitrification.After successful start-up,the effects of different S/N ratio,HRT and temperature on the reaction process were investigated to improve the accumulation effect of NO₂^--N and S⁰.In addition,the recovery of S⁰ is also a noteworthy problem.In this study,the method of flocculation and precipitation was used to separate biological elemental sulfur from wastewater.Secondly,this study also investigated the effect of different elemental sulfur sources（biological elemental sulfur and chemical elemental sulfur）on the denitrification performance of Anammox synergistic denitrification to improve the total nitrogen（TN）removal rate.Finally,the efficiency of two-stage sulfide autotrophic partial denitrification coupled Anammox combined process to treat wastewater containing nitrate and sulfide was explored after the optimization of working conditions,in order to provide theoretical guidance and reference for practical engineering applications.This study proposes the following research contents:（1）Start-up of partial sulfide autotrophic denitrificationThis study investigated the effect of seeding sludge on PSAD process by using nitrate（NO₃^--N）and sulfide(S^2--S)as influent substrates,with the sludge taken from the oxidation zone（S-o）of wastewater treatment plants,partial denitrification reactor(S-_PD),and anoxic/oxic reactor(S-_A/O).The results showed that PSAD process could be realized rapidly in three systems,especially,the S-_O system completed the start-up in the shortest time of 22 d,with NO₃^--N and S^2--S removal rates of 85.3%and 99.3%,respectively.Nitrite and elemental sulfur accumulation rates were 89.12%and 62.16%,respectively.On the 29^th day of S-_PD system,the nitrite accumulation rate increased to 84.70%,and the S⁰ accumulation rate was 67.52%.In the S-_A/O system,the nitrite accumulation rate was 82.87%,S⁰ accumulation rate was 69.24%on the 26^th day.（2）To explore the accumulation effects of different influencing factors on nitrite and elemental sulfur in the PSAD process（1）After the PSAD process was successfully started,the nitrite and biological elemental sulfur accumulation efficiency were explored under different S/N ratios（ranging 0.71-1.2）,and it indicated that when the S/N ratio was 1.1,the NO₂^--N and S⁰ accumulation were optional at the same time,which were 85.2%and 73.5%,respectively.（2）When HRT was controlled for 6h,5h and 4h,the nitrite accumulation rate reached71.74%,91.61%and 94.83%on average,respectively.Excellent nitrite accumulation effect was achieved when HRT was 5h and 4h.In terms of elemental sulfur accumulation,the average sulfur accumulation rate reached 79.6%when HRT was 5h.when HRT was 4h,the effect of sulfur autotrophic denitrification deteriorated,the elemental sulfur accumulation was only20.83%.Comprehensive HRT of 5h can realize sufficient nitrite and elemental sulfur accumulation synchronously.（3）The average sulfur accumulation rates at 25℃and 30℃were 77.1%and 72.8%,respectively,which achieved relatively stable accumulation of target products.The results showed that the change of system temperature in a certain range had little influence on the effect of sulfide removal and elemental sulfur accumulation in the reaction process,which can achieve stable results.（4）Through high-throughput sequencing analysis of sludge samples,Thiobacillus is a typical autotrophic denitrifying bacterium belonging to Proteobacteria.Thiobacillus is the main contributor to the PSAD process,and its high abundance（66.04%）is the key to realize the accumulation of sulfur and nitrite.With Thiobacillus as the dominant bacterium and the coordination of Arenimonas and Thauera,the efficient nitrogen and sulfur removal in the partial sulfide autotrophic denitrification process is ensured.（3）Research on recovery of biological elemental sulfurIn the batch flocculation experiments,the separation of S⁰ in the effluent was performed using flocculation.Employing polyaluminum chloride（PAC）as flocculant,the batch test evaluated the effects and interactions of PAC dosage and p H on the treatment efficiency of the S0 flocculant rate（SFR）.Using 2D Gaussian function as quadratic model,an optimal condition of PAC dosage 7.92 ml/L and p H 5.14 were obtained,and the SFR reached 94.1%during optimum flocculation conditions.（4）Study on synergistic denitrification and denitrification of Anammox by different sulfur sourcesWhen chemical sulfur source was added in R1 system,16.71%TN was removed by sulfur autotrophic denitrification（S⁰-SAD）after 72 to 78 days,and the average TN removal rate reached 96.12%.When biological sulfur source was added in R2 system,the average TN removal rate of S⁰-SAD was 96.91%,and the highest was 98.31%.TN was mainly removed by Anammox and elemental sulfur autotrophic denitrification（A/S⁰-SAD）.The TN removal rate of A/S⁰-SAD system increases with the increase of the TN removal rate of S⁰-SAD pathway.The denitrification rate of R2 biological sulfur type（2.45 mg NO₃^--N/（L·d））was higher than that of R1 chemical sulfur type（1.78 mg NO₃^--N/（L·d））.This is because the formation of elemental sulfur particles generated by biological reaction is a complex aggregate composed of elemental sulfur,biomass and biopolymer.This structure increases the bioavailability of elemental sulfur particles to microorganisms,thus increasing the reaction rate.However,when chemical sulfur was used as the electron donor of sulfur autotrophic denitrification,its very low water solubility seriously affects the process of sulfur transfer from solid to liquid phase,and further limits the degree of sulfur participation in the reaction,resulting in an increase in the operation cycle when achieving stable removal effect.（5）Combined process of sulfur autotrophic short-cut denitrification and coupled Anammox processThe feasibility and stability of coupling process for treating wastewater containing nitrate and sulfide were studied by combining partial sulfide autotrophic denitrification SBR reactor and Anammox ASBR reactor.The effluent of the front SBR reactor was taken as the influent of the rear ASBR reactor.The test results showed that:In the early stage of coupled operation（1-25 days）,the TN removal rate fluctuated,and the average TN removal rate was 85.6%,closed to the theoretical maximum TN removal rate of 89%.In the late stage of operation,the TN removal rate of the system gradually increased,and finally stabilized at 93.8%,which may be attributed to the removal of nitrate in the Anammox process by S⁰ in the effluent in the early stage.The results showed that PSAD coupled with Anammox process could not only avoid the inhibition of high sulfide concentration on Anammox bacteria,but also improve the removal efficiency of TN.