Study On The Effect Of Sponge Iron On The Sart-up Of Anammox

At present,Anammox bacteria（abbreviated as An AOB bacteria）prevalently have a long generation cycle,harsh growth conditions and difficulty in enrichment.Besides,the slow start-up speed and the theoretical TN removal rate of the anammox reaction does not exceed89%,which make this process rarely applied to the treatment process of urban sewage.In order to shorten the start-up time of the anammox reactor and enhance the denitrification performance of the system,a more direct and effective way is to add trace metal element iron.Different inoculated sludge has a greater impact on the start-up of anammox.The selection of inoculated sludge determines the start-up time of the reactor to a certain extent.Studies have shown that An AOB bacteria can use certain organic matter as electron donors to reduce NO₃^--N.In the actual urban sewage treatment process,organic matter is inevitable,and low-concentration organic carbon sources can induce mixed nutrient anammox to start.However,few scholars have studied the influence of iron on the start-up and denitrification process of anammox for different types of inoculated sludge and different types of nitrogen-containing wastewater.Therefore,the biological iron sludge with high microbial diversity and various iron forms obtained by long-term domestication of sponge iron（a typical zero-valent iron material）in the laboratory and the activated sludge from the secondary settling tank of the sewage treatment plant are used as the inoculation sludge.At the same time,it is aimed at two types of wastewater with low nitrogen and low carbon to nitrogen ratio.Sponge iron is to study sponge iron to strengthen different inoculation sludge systems and to treat different types of nitrogen-containing wastewater in a targeted manner.It is of great significance for improving the start-up time of the anaerobic ammonia oxidation system,enhancing the TN removal efficiency,and realizing the industrial application of the technology.In this study,simulated wastewater with a typical NO₂^--N and NH₄⁺-N ratio of 1.32±0.3was used as the target pollutant.Take the ordinary sludge R0 system and the iron sludge R1system as blank control.The start-up of the anaerobic ammonia oxidation reaction of different inoculated sludge systems with sponge iron was studied（ordinary sludge R0+sponge iron SFe system,iron sludge R1+sponge iron SFe system）;At the same time,with the R0 system as a control,the process of start-up the mixed nutrient anammox reaction of the sponge iron-enhanced ordinary sludge system（ordinary sludge R0+sodium acetate C system,ordinary sludge R0+sodium acetate C+sponge iron SFe system）;Finally,the mechanism of denitrification in the R1 system was explored.The main findings were as follows:（1）The effect of sponge iron on the anaerobic ammonia oxidation start-up of different inoculated sludge systems showed that,the start-up speed:R0>R1>R1+SFe>R0+SFe;After each reactor was running stably,the TN removal rate:R1+SFe>R1>R0>R0+SFe;Specific anammox activity:R0>R1>R0+SFe>R1+SFe.The intervention of sponge iron inhibits the specific anammox activity,thereby inhibiting the start-up process of anammox in the R0+SFe system and R1+SFe system,but promotes the removal of TN in the R1+SFe system.After stable operation,the iron sludge R1+SFe systemΔNO₂^--N/ΔNH₄⁺-N andΔNO₃^--N/ΔNH₄⁺-N were closer to the anaerobic ammonia oxidation reaction stoichiometric ratio 1.32 and 0.26;Due to the diversity of iron forms and microorganisms in the system,it is likely that other biochemical reactions involving iron accelerate the conversion of nitrogen,thereby improving the TN removal effect of the system.The low specific anammox activity and high TN removal rate of the R1,R1+SFe system once again indicate the existence of other biochemical reactions in the iron sludge system.（2）With the increase of nitrogen load,the R1+SFe system had the best TN removal rate,followed by the R1 system,and the R0 system had the most unstable denitrification effect.And with the increase of nitrogen load,each systemΔNO₂^--N/ΔNH₄⁺-N andΔNO₃^--N/ΔNH₄⁺-N were getting closer and closer to the theoretical value 1.32 and 0.26 of the stoichiometric ratio of the anaerobic ammonia oxidation reaction,indicating the increase of nitrogen load was beneficial to the process of the anaerobic ammonia oxidation reaction.The intervention of sponge iron reduced the accumulation of NO₃^--N in the R1+SFe system,making the average value of the systemΔNO₃^--N/ΔNH₄⁺-N lower than that of the R1 system.（3）The effect of sponge iron on the anaerobic ammonium oxidation start-up of the mixed nutrient general sludge system showed that the start-up speed R0+C+SFe>R0+C;After the reactor runed stably,the TN removal rate was R0+C>R0+C+SFe;the specific anammox activity was R0+SFe+C>R0+C.It shows that the intervention of sponge iron is beneficial to the higher specific anammox activity of the R0+SFe+C system,which is an important reason for the fast start-up speed of this system,but it has an inhibitory effect on the removal of TN.After stable operation,the R0+C+SFe systemΔNO₂^--N/ΔNH₄⁺-N was lower than the R0+C system;The intervention of sponge iron is not conducive to the conversion of NO₂^--N,and may interfere with the traditional anaerobic ammonia oxidation coupled denitrification system.Therefore,the TN removal rate of the R0+C+SFe system was low.Compared with the R0system,the intervention of sodium acetate,sodium acetate+sponge iron inhibited the start of the anaerobic ammonia oxidation of the R0+C,R0+C+SFe systems,but the TN removal rate after stable operation was much better than that of the R0 system;At the same time,the R0+C,R0+C+SFe systemΔNO₃^--N/ΔNH₄⁺-N was far lower than the R0 system,so it can explain the high TN removal rate of these two systems.It also reflects the advantages of low-carbon-nitrogen ratio wastewater inducing mixed nutrient anaerobic ammonia oxidation reaction.（4）According to the changes in nitrogen and iron concentrations in a typical operating cycle,the average values ofΔNO₂^--N/ΔNH₄⁺-N for R0 and R1 systems were 1.34 and 2.09,respectively.In addition,the Fe²⁺in the mixed solution of the R1 system first decreased and then increased during the reaction,indicating that other biochemical reactions involving Fe²⁺in the R1 system inhibited the start-up process of the anammox reaction and also prolonged the activity increase period of the R1 system.When the water intake strategy of the R1 system was changed,An AOB bacteria,iron ammonia oxidizing bacteria and iron denitrifying bacteria may use Fe³⁺or Fe⁰/Fe²⁺existing in the system to cause iron ammonia oxidation and iron denitrification,showing the diversity of biochemical reactions in the R1 system and the reason for the high TN removal rate.When the R1 system continued to feed water with only NH₄⁺-N,the iron ammonia oxidation reaction of the system weakened first and then gradually recovered.After recovery,the average TNRE can reach 21.02%;When the R1 system continued to enter water only NO₂^--N,the iron-type denitrification reaction of the system gradually become weaker,and the oxidation reaction of NO₂^--N to NO₃^--N by high-valent iron gradually become dominant.The average TNRE at this stage can reach 25.81%.（5）During the startup of R0 and R1 reactors,the relative abundance of the dominant bacteria phyla Bacteroidetes,Chloroflexi and Planctomycetes,as well as the dominant Ignavibacteria belonging to the phylum Ignavibacteria,increased,Which was conducive to the further enrichment of An AOB bacteria;Acidobacteria,which grows in an iron-rich environment and can participate in the iron cycle,are also further enriched in the R1 system,and their relative abundance rises from 7.08%to 11.16%.The emergence of dominant genus such as Terrimonas,norank＿c＿OM190,PHOS-HE36,Denitratisoma,Limnobacter,etc.,indicates that the microbial flora of the R0 and R1 reactors have undergone major changes during the 80-day anaerobic ammonia oxidation reaction start-up process,and are gradually approaching successful start-up.The appearance of norank＿c＿OM190（4.46%）belonging to the planktonic fungus phylum in the R0 system indicates that the R0 reactor is closer to the start-up success;The appearance of Desulfuromonas,which participates in iron reduction in the R1 system,and Thiobacillus,which uses iron as an electron donor for autotrophic denitrification,indicate that there are other biochemical reactions involving iron in the R1system during the initiation of the anammox reaction,such as iron-type denitrification.This further explains the reason for the good denitrification effect of the R1 system.