Study On Nitrogen And Sulfur Removal Performance By Coupling Autotrophic/Heterotrophic Denitrification And Anaerobic Ammonium Oxidation

With the accelerated industrialization,the wastewater discharge from oil refining and pharmaceutical industries has increased.Such wastewater contains large amounts of carbon,nitrogen and sulfide pollutants,which will seriously threaten ecological safety and human health if discharged without treatment to meet the standards.Anaerobic ammonia oxidation（ANAMMOX）technology has the advantages of being green and efficient,energy-saving and environmentally friendly.However,the process uses nitrite（NO₂^--N）as the electron acceptor,and its stable source is the key to the successful operation of ANAMMOX.The autotrophic/heterotrophic short-cut denitrification process,which uses sulfide and organic simultaneously as electron donors to reduce nitrite（NO₃^--N）to NO₂^--N,can provide NO₂^--N for the ANAMMOX reaction,and through the reasonable optimization of operating parameters,it can efficiently and stably provide the reaction substrate for ANAMMOX,thus achieving the simultaneous removal of carbon,nitrogen and sulfide pollutants.In this experiment,we firstly initiated the sulfur autotrophic/heterotrophic short-cut denitrification process and obtained stable accumulation of NO₂^--N by optimizing the S/N/C substrate ratio for pollutant removal,and then designed batch experiments to investigate the effects of different temperatures,p H and NO₃^--N concentrations on the operational performance of the system.Secondly,this study used different concentrations of sulfide injection into the ANAMMOX reactor to synergize ANAMMOX deep denitrification with sulfide autotrophic denitrification.In addition,trace amounts of hydrazine were added to the ANAMMOX reactor to inhibit the growth of nitrite oxidizing bacteria and enhance the activity of ANAMMOX bacteria.Finally,the pollutants removal performance of the autotrophic/heterotrophic short-cut denitrification-ANAMMOX process was investigated under the optimal working conditions,in order to provide some theoretical references for the treatment of practical wastewater.The main contents of this study are as follows:（1）Start-up and operation characteristics analysis of autotrophic/heterotrophic short-cut denitrification processSulfur autotrophic/heterotrophic short-cut denitrification can overcome the shortcomings of a single autotrophic heterotrophic denitrification process,achieve efficient pollutant removal and stable accumulation of NO₂^--N while reducing secondary pollution,and provide a green and efficient reaction substrate for the ANAMMOX process.With the combination of sulfide and organic as the electron donor for denitrification,the autotrophic/heterotrophic short-cut denitrification was successfully initiated within 20 days,the removal rate of the sulfur sulfide,nitrate and organic carbon was 95.93%,80.60%,81.61%,and the nitrate concentration was reduced to 6.66 mg/L,and NAR reached 81.47%;the best performance of short-cut denitrification was achieved when the S/N/C control was 3/4/9,and the NAR was as high as 94.24%,and the effluent SO₄^2--S concentration was only 12 mg/L.The contribution of autotrophic and heterotrophic denitrification was 55.07%and 44.93%,respectively.The results of batch tests examining the effects of NO₃^--N concentration（35 mg/L,45 mg/L,55mg/L and 65 mg/L）,p H（6.5,7.0,7.5 and 8.5）and temperature（15°C,20°C,28°C and 33°C）on the performance of short-cut denitrification in mixotrophic showed that the accumulation concentration of NO₂^--N was positively correlated with the initial NO₃^--N concentration;the conversion rate of NO₃^--N→NO₂^--N was faster at p H 7.5 and temperature 28°C,and the short-cut denitrification performance was optimal.In addition,kinetic modeling,X-ray electron spectroscopy and microbial sequencing were used to reveal the pollutant removal mechanism and conversion characteristics of the mixotrophic short-cut denitrification system.The kinetic parameters under different S/N/C differed significantly,the denitrification rate accelerated gradually with the change of S/N/C ratio,the microbial adaptability to different substrate ratios increased gradually,and the maximum denitrification efficiency R_m showed an increasing trend.S^2--S oxidation process produces products such as S⁰,S_n^2-and SO₄^2-,and multiple S valence states participate in the denitrification process.Form electron buffer effect,further ensure the efficient removal of sulfur and nitrogen.Microorganisms showed significant differences at the genus level with changes in the S/N/C,with Thiobacillus dominating the autotrophic system and gradually decreasing the relative abundance in the mixotrophic system,and increasing the abundance of Halomonas and Pseudomonas.There is no absolute dominant genus in the mixotrophic system,and the autotrophic,heterotrophic and parthenogenic bacteria coexist harmoniously,with Thiobacillus,Halomonas and Pseudomonas were the dominant genera,and they cooperated with Thauera and Alishewanella to complete the short-cut denitrification process of mixotrophic.（2）Effect of sulfide on the denitrification performance of ANAMMOXANAMMOX coupled sulfur autotrophic denitrification is an effective method for deep nitrogen removal from wastewater.By adding sulfide to remove the by-product NO₃^--N of ANAMMOX reaction,the coupled process can promote the deep denitrification.Adding a certain concentration of sulfide to ANAMMOX system can domesticate part of sulfur autotrophic denitrifying bacteria after long-term culture,and achieve deep nitrogen removal by denitrification.When the sulfide concentration was 15 mg/L,the system can maintain the good denitrification performance of ANAMMOX while obtaining a low effluent NO₃^--N concentration,and the contribution of denitrification can reach 10.46%.S^2--S concentration exceeded 20 mg/L significantly inhibited the nitrogen removal activity of ANAMMOX,and the nitrogen removal efficiency decreased to less than 50%.The contribution of denitrification was positively correlated with the sulfide dosing concentration,increasing from 5.71%to36.95%,and the contribution of ANAMMOX was conversely reduced from 94.28%to63.05%.The kinetic model and microbial sequencing revealed the removal characteristics of the pollutants.When the sulfide concentration was 30 mg/L,the maximum denitrification rate R_m value was the smallest,the denitrification delay timeλwas the largest,and the activity of ANAMMOX bacteria was the lowest,making it difficult to achieve efficient denitrification.The abundance and diversity of microbial communities increased with the increase of sulfide concentration,and autotrophic denitrifying bacteria such as Thiobacillus,Azoarcus and Alishewanella were gradually domesticated in the system,while the abundance of ANAMMOX bacteria Candidatus-Brocadia decreased from 47.03%to 30.65%,but it was always dominance in the system.（3）Investigation of the operational performance of the coupled autotrophic/heterotrophic short-cut denitrification-ANAMMOX processHydrazine,as an intermediate product of ANAMMOX,can inhibit the growth of nitrite oxidizing bacteria in the system and enhance the denitrification activity of ANAMMOX bacteria.The two-stage process of autotrophic/heterotrophic short-cut denitrification-ANAMMOX can achieve stable and efficient simultaneous denitrification,decarbonization and sulfide removal.The total nitrogen removal rate of the system could be restored to83.95%by adding 4.5 mg/L hydrazine to the long idle anaerobic ammonia oxidation reactor.The three stages of ANAMMOX with feed water substrate ratios of 1.12,1.32 and 1.45 could achieve almost 99%removal efficiency of NH₄⁺-N and NO₂^--N,reflecting the high efficiency and stability of the two-stage coupled process.In addition,the occurrence of sulfide autotrophic denitrification also promoted the deep denitrification of the ANAMMOX system.The results of denitrification contribution analysis showed that with the change of influent substrate ratio and long-term sulfide dosing,the nitrogen removal contribution of denitrification increased,but the ANAMMOX reaction was always the main pathway for nitrogen removal in the system.