Study On Nitrogen Removal Performance Of Partial Nitrification Inhibited By Hydroxylamine Coupled With Anammox Process

In recent years,water eutrophication has become increasingly serious,wastewater denitrification is an important means to eradicate water eutrophication,and partial-nitritation/Anammox process is an ideal denitrification sewage treatment process for sewage treatment plants.In the long-term operation of partial nitrification,the stable accumulation of nitrite（NO₂^--N）has become one of the biggest challenges.Although stable NO₂^--N accumulation strategies have been proposed in many studies,due to the adaptability of nitrite oxidizing bacteria（NOB）,these inhibition strategies fail during long-term operation to collapse the partial nitrification system,anaerobic ammonia-oxidizing bacteria（An AOB）are autotrophic bacteria that proliferate slowly and cannot be enriched quickly,resulting in long system start-up time and low nitrogen removal efficiency.Therefore,in this study,the optimal dosing concentration of hydroxylamine（NH₂OH）in the partial nitrification system and the effect of NH₂OH on the activity and kinetic parameters of nitrifying bacteria were first studied through batch tests,and partial nitrification was quickly started on this basis.During the long-term operation of NH₂OH inhibition partial nitrification,the stable operation of hydrazine（N₂H₄）was optimized by alternating dosing.Secondly,the effects of NH₂OH and N₂H₄ on the denitrification performance of the Anammox system were explored,and the changes of total nitrogen（TN）,stoichiometric ratio and microbial community of the effluent of the Anammox system were supplemented with the laboratory initiated Anammox sludge,and NH₂OH and N₂H₄were added to the Anammox system,respectively.Finally,on the basis of NH₂OH inhibition partial nitrification,partial nitritation was achieved by adjusting the aeration method,the nitrogen removal efficiency of two-stage partial nitritation coupled with Anammox combined process for domestic sewage is explored,in order to provide a theoretical basis for the long-term stable operation of partial-nitritation coupled with Anammox.The main research contents are as follows:（1）Start-up of partial nitrification inhibited by NH₂OHThe effects of hydroxylamine（NH₂OH）on the activity and kinetic parameters of nitrifying bacteria（AOB）and the recovery of AOB activity after AOB inhibition were investigated using SBR to treat synthetic domestic sewage.Results of batch test showed that when the concentration of NH₂OH was 4.5 mg/L,the activity of AOB showed the highest activity,the activity of NOB decreased,and the oxidation rate of NO₂^--N（）decreased to8.00 mg/（L·h）.The half-saturation constant of NO₂^--N（）increased to 7.77 mg/L,indicating that the inhibition type of NH₂OH on NOB was mixed inhibition.With the addition of 4.5 mg/L of NH₂OH to SBR,the accumulation of nitrite reached 95.85%at the 6th day.When the concentration of NH₂OH was increased to 10 mg/L,the activity of AOB and NOB decreased.The addition of NH₂OH was stopped,the DO increased from 2±0.3 mg/L to 3±0.3mg/L,and the NAR recovered from 13.42%to 95.78%.（2）Optimization of long-term stable operation of partial nitrification inhibited by NH₂OHAfter NH₂OH inhibition partial nitrification was successfully started,the changes of nitrogen removal performance and AOB and NOB activities of partial nitrification during long-term operation were explored.On this basis,the long term stable operation of NH₂OH inhibition partial nitrification was optimized by alternating NH₂OH and N₂H₄.The results showed that:（1）4.5 mg/L of NH₂OH was added to R2 per cycle,and after 52 days of operation,the accumulation of nitrite dropped to less than 60%,the partial nitrification system collapsed,and the NH₂OH concentration needed to be continuously increased to maintain stable NO₂^--N accumulation.During long-term operation,the adaptability of NOB flora to NH₂OH gradually increased,and the time for NO₂^--N to maintain stable accumulation was shorter.（2）Through NH₂OH and N₂H₄ mixed dosing experiments in different proportions,it was found that NH₂OH and N₂H₄ had different inhibition mechanisms for NOB.In order to optimize the stable operation of NH₂OH suppressed partial nitrification,after the partial nitrification was successfully achieved by adding NH₂OH to the SBR,the stable operation of partial nitrification was realized by alternately adding 4.5 mg/L of NH₂OH or N₂H₄ every cycle.In the later stage,NH₂OH or N₂H₄ was added every 7 days,and accumulation of nitrite was maintained at more than 90%after 120 days of operation.（3）At the 121st day,the influent water of the stably running SBR reactor was changed from synthetic wastewater distribution to actual domestic sewage,and the ammonia nitrogen removal rate and nitrite accumulation rate also recovered to more than 95%on the 138th day,but the COD removal rate only reached 57%when it was the highest.Nitrifying bacteria in the system still predominate.（4）The microbial communities of partial nitrification inhibited by NH₂OH were analyzed,and the relative abundance of AOB increased and the relative abundance of NOB decreased after NH₂OH and N₂H₄.After the addition of NH₂OH and N₂H₄,Nitrospira migrated to Candidatus＿Nitrotoga,and in the R2 reactor with only NH₂OH,the migration rate was significantly faster than that of the R3 reactor where NH₂OH and N₂H₄ were alternately dosed,and it was found that NH₂OH had no inhibitory effect on Candidatus＿Nitrotoga,but had a strong inhibitory effect on Nitrospira.（3）Study on nitrogen removal performance of Anammox by adding NH₂OH and N₂H₄In order to explore the effects of NH₂OH and N₂H₄ on the denitrification performance of the Anammox system alone and the changes of microbial communities,NH₂OH and N₂H₄were added to the A1 and A2 reactors to achieve stable nitrogen removal performance.The results showed that:（1）4.5mg/L NH₂OH was added per cycle to the A1 reactor,the total nitrogen removal rate reached 94.23%,and the values of△NO₂^--N/△NH₄⁺-N and△NO₃^--N/△NH₄⁺-N were1 and 0.1,respectively.Compared with the initial stage,the nitrogen removal performance of the anaerobic ammonia oxidation system is significantly improved.（2）4.5mg/L N₂H₄ was added per cycle in the A2 reactor,and the total nitrogen removal rate reached 97.16%,and the values of△NO₂^--N/△NH₄⁺-N and△NO₃^--N/△NH₄⁺-N were0.96 and 0.04,respectively.Compared with the A1 reactor,the nitrogen removal of the N₂H₄anaerobic ammonia oxidation system is better.（3）The analysis of the microbial communities in the original sludge and A1 and A2reactors,the relative abundance of anaerobic ammonia oxidizing bacteria Candidatus＿Brocadia increased by more than 10%after the addition of NH₂OH and N₂H₄,respectively,but the relative abundance of denitrifying bacteria in A1 reactor was higher than that of A2 reactor.（4）Study on the nitrogen removal performance of partial nitrification inhibited by NH₂OH coupled Anammox（1）After adjusting the aeration mode of partial nitrification to aerobic/anoxic（30 min/30min）alternating mode,partial nitritation was realized within 6 days,and the NO₂^--N/NH₄⁺-N of the effluent was 0.93.Partial nitritation effluent is used as the feed water for Anammox.The test results show that the NH₂OH inhibitory partial nitritation coupled Anammox process treated actual domestic sewage,and when the combined process is run to the 20th day,the effluent concentrations of NH₄⁺-N,NO₂^--N and NO₃^--N were 1.29,1.01 and 2.26 mg/L,the ammonia nitrogen removal rate was 97.95%,and the TN in the effluent droped to 4.57 mg/L.The COD concentration of the effluent was 48.4 mg/L,and the COD removal rate was81.29%.After that,the TN in the effluent was stable at about 5 mg/L,and the COD removal rate remained above 80%.（2）The economic analysis of partial nitrification inhibited by NH₂OH coupled Anammox and denitrification process was carried out,and compared with the traditional nitrification and denitrification process,NH₂OH inhibited partial nitrification coupled with Anammox nitrogen removal process can save more than 95%of the pharmaceutical cost.