Recovery Characteristics And Mathematical Simulation Of SAD Biological Nitrogen Removal Process After High Salinity Shock

The pollution of high-salt nitrogen-containing wastewater in our country is becoming more and more serious,and the sewage discharge standards are becoming more and more strict.It is an urgent task to explore efficient and stable biological denitrification processes.Although simultaneous anammox and denitrification（SAD）process can achieve high-efficient and synergistic denitrification,high saline wastewater will destroy the stability of the SAD system during the reaction.In response to this problem,this paper studies the recovery characteristics of the SAD process after high salinity shock.Therefore,this paper explores the recoveries of the anammox process and the SAD process in a phased manner.On this basis,the models of anammox process recovery and SAD process recovery are established,and the optimization of the SAD process recovery is mathematically simulated.The optimal C/N ratio was determined and the process recovery conditions are optimized to achieve efficient recovery and stable operation of the SAD process,in order to provide theoretical guidance and prediction for the SAD process recovery system stability and efficient treatment of nitrogen-containing organic wastewater.The main conclusions are as follows:（1）Study on recovery of anammox process.The recovery and operational characteristics of Anammox process after the high salinity shock were investigated by stepwisely increasing influent total nitrogen loading（NLR）from 0.17 Kg/（m³·d）to 1.05Kg/（m³·d）in an upflow anaerobic sludge blanket（UASB）reactor.After operating for141 days,the removal efficiencies of NH₄⁺-N,NO₂^--N and TN reached 95.37%,93.36%and 81.42%,and the total nitrogen removal loading（NRR）reached 0.85 Kg/（m³·d）,which was attributed to the effective recovery of Anammox sludge activity.With the recovery of the process performance,the color of the granular sludge turned from deep brown to red brown,and the average particle size increased,among which granules with particle size larger than 1.5 mm accounted for the maximum proportion of 68.25%;Moreover,the EPS content increased from 105.89 mg/g to 147.98 mg/g,and the EPS_P/EPS_Cratio increased from 6.05 to 13.34,which further proved that the anammox process recovered to an efficient operational state.（2）Research on recovery of SAD process.After the restoration of the anammox process was completed,a low concentration of organic carbon source（sodium acetate）was added to maintain the C/N ratio at around 0.25.After 53-day operation,the DNB activity was recovered.The removal efficiencies of NH₄⁺-N,NO₂^--N and COD reached93.43%,91.79%and 82.22%,respectively,and the NRE,NRR and total nitrogen loading（NLR）reached 82.99%,0.90 Kg/（m³·d）and 1.09 Kg/（m³·d）,respectively.With the resumption of the coupling process,the color of the granular sludge changed from reddish brown to off-white,and was partially wrapped.The addition of organic carbon sources increases the overall particle size of the granular sludge.The percentage of sludge larger than 1.5 mm was 72.06%with an increase of 3.81%compared with the previous stage.At the same time,the EPS content continues to rise.When it runs to Day194,the EPS content in the reactor rises to 203.53 mg/g（calculated by VSS）,thus achieving the SAD process recovery.（3）Optimize the mathematical simulation of SAD process recovery performance.Firstly,the SAD process recovery model was constructed based on the experimental data and the improved mathematical model（ASM1）.The experimental data and the simulated data were compared and analyzed.At the end of the simulated recovery period（Day 194）,the experimental value of the NRE and the simulated value reached82.99%and 82.90%,respectively,and the effectiveness of the model was verified.Secondly,through model analysis,the changes of microorganisms during the SAD recovery process were discussed.Finally,through simulation and prediction,the denitrification performance and changes of functional bacteria in the coupled system at different C/N ratios were investigated.The simulation results showed that as the C/N ratio increases（0.3～1.0）,the growth rate of An AOB concentration and activity gradually decreased,whereas those of DNB gradually increased.In addition,the NRE gradually increased when the C/N ratio increased from 0.3 to 0.6,indicating that the synergistic effect of An AOB and DNB gradually enhanced,and the NRE gradually decreased when the C/N ratio increased from 0.6 to 1.0,indicating that the synergistic effect gradually decreased and the competitive effect gradually increased.At the same time,it showed that when the C/N ratio reached 0.6,the best synergism of An AOB and DNB was obtained and the NRE was stabilized at about 85.35%.At this time,the contribution rate of nitrogen removal by An AOB was 83.33%,and that by DNB was16.67%.