Effects Of Iron Dosage On Nitrogen Removal Performance And Microbial Population Structure Of Biological Sponge Iron System

Nitrogen-containing wastewater pollution is one of the major environmental pollution problems.At present,the treatment methods of nitrogen-containing wastewater include physical and chemical methods and biological methods.The physical and chemical methods have high operating costs,are easily brought into secondary pollution,and have poor impact load resistance.Therefore,biological methods have become a hot spot in the field of wastewater treatment research.The traditional biological denitrification includes two stages of aerobic nitrification and anoxic denitrification.The two processes have very different environmental requirements.Therefore,there are excessive energy consumption,additional carbon source and alkalinity during operation,Large area and complicated operation.In recent years,studies have found that adding a certain amount of Fe²⁺or Fe³⁺to the activated sludge system can enhance the biological denitrification effect.Iron as a kind of active metal,when adding Fe0 to the bioreactor,it can not only play the role of biological iron,but also greatly improve the nitrogen removal effect.Sponge iron is a porous substance with high Fe⁰ content,which can combine well with activated sludge to form a biological sponge iron system?BSIS?.The production of iron ions plays an important role in the BSIS action,and the amount of iron input is the direct factor of iron ion production.Therefore,this paper takes simulated domestic sewage as the research object,starts the SBR reactor with iron dosage of 0,45,90 and 135 g/L in parallel,compares the degradation organic matter and nitrogen removal ability of each system,and determines the number of nitrogen removal bacteria in each system with stable operation.In actual sewage treatment structures,microorganisms may face temporary nutrient deficiency environment due to the periodic fluctuation of water intake,so the effect of iron input on nitrogen removal performance and nitrifying bacteria activity under aerobic starvation conditions was investigated.High throughput technique was used to analyze the changes of microbial community structure between the common activated sludge system and the biological sponge iron system with 45 g/L of iron input from start-up to stable operation.The characteristics of simultaneous nitrification and denitrification under the synergistic action of iron and microorganism were revealed,which laid the foundation for the engineering application of this method.The main findings are as follows:?1?When the amount of iron added is different,the difference in the degradation capacity of COD_Crr is small,the removal rate of COD_Crr in each system can reach more than95%.The removal rate of NH₄⁺-N in activated sludge system with iron content of 0,45,90,135g/L is 98.21%,98.76%,99.05%,98.79%,and the NO₂^--N effluent concentration is basically 0.00mg/L.It shows that the iron dosage has little effect on the degradation of COD_Cr,NH₄⁺-N,NO₂^--N.The TN removal rate of each reactor was 43.72%,50.99%,62.53%,56.89%,indicating that the intervention of sponge iron obviously promoted the denitrification,thereby improving the TN removal rate significantly.The changes of the concentration of NH₄⁺-N,NO₂^--N,NO₃^--N in each reactor with stable operation in one cycle were measured,finding that the synergistic effect of microorganism and sponge iron accelerates the removal rate of NH₄⁺-N,NO₂^--N,NO₃^--N in the reactor and improves the impact load resistance of the reactor,in which the removal effect is the strongest when the iron input is 90 g/L.?2?The nitrogen removal effect of each system during the 7d aerobic starvation period and the 7d recovery period was investigated.The results showed that aerobic starvation had little effect on the degradation of COD_Cr,and the removal rate of iron content 45,90,135 g/L activated sludge system increased by 2.02%,4.04%and 2.69%respectively,compared with NH₄⁺-N common activated sludge system in the first day of influent recovery was restored.The nitrite accumulation rate decreased by 7.48%,8.57%,8.12%,and the NO₃^--N effluent concentration decreased by 3.03mg/L,6.04mg/L,4.25mg/L.Therefore,with the increase of iron content,the promotion effect of iron on recovery ability is greater.When the iron content is 90g/L,the promotion effect on recovery ability is most significant.When the iron content exceeds 90g/L,the promotion effect on recovery ability is weakened.?3?The activities of nitrifying bacteria AOB and NOB in 7d aerobic starvation period and 7d recovery period were investigated.The study found that the active decay rate of AOB in the activated sludge system with iron content of 0,45,90,135g/L is 0.144d^-1,0.129d^-1,0.114d^-1,0.122d^-1,and the active decay rate of NOB is 0.157d^-1,0.150d^-1,0.140d^-1,0.143d^-1,indicating that the decay rate of NOB activity is greater than AOB.With the increase of iron content,the decay rate of nitrifying bacteria decreases.When the iron content is 90g/L,the decay rate is the smallest.When the iron content exceeds 90g/L,the decay rate increases slightly.AOB the activity recovery rate was 0.087d^-1,0.092d^-1,0.100d^-1,0.098d^-1,NOB the activity recovery rate was 0.091d^-1,0.105d^-1,0.121d^-1,0.117d^-1,so the nitrite accumulation phenomenon disappeared in each reactor at the 7th day.In the early recovery period,the activity recovery rate of AOB is greater than that of NOB,so the nitrous nitrogen accumulation phenomenon occurred in the early recovery period.As the iron content increases,the recovery rate of nitrifying bacteria increases.When the iron content is 90g/L,the recovery rate is the largest.When the iron content exceeds 90g/L,the decay rate decreases slightly.The activity of nitrifying bacteria did not recover to the level before the experiment,indicating that the recovery of microbial activity is slower than the recovery of the system's denitrification capacity.?4?The amount of denitrifying bacteria in the system with stable operation of sponge iron dosages of 0,45,90,and 135g/L was determined.The number of ammonia-oxidizing bacteria is 9.5*10³,11.5*10³,16.5*10³,13.0*10³?/mL,and the number of nitrate bacteria is5.5*10⁴,6.2*10⁴,13.0*10⁴,9.5*10⁴?/mL,the number of denitrifying bacteria is 2.0*10⁴,3.0*10⁴,20.0*10⁴,9.5*10⁴?/mL.From the data,it can be seen that the number of nitrogen-removing bacteria in the biological sponge iron system is higher than that in the ordinary activated sludge system,in which the amount of iron input is the highest at 90 g/L.which indicates that sponge iron promotes the growth of microorganisms in the system,thus improving the denitrification effect,promotion effect is weakened when the dosage is too much.?5?The initial sludge of the reactor has the highest microbial abundance and diversity,followed by the biological sponge iron system,and the ordinary activated sludge has the lowest.At the gate level,the predominant phylum of each sample is the same,but the proportion has changed.Among them,Proteobacteria has the largest proportion,46.91%in the initial sludge,and compares in the ordinary activated sludge and biological sponge iron increased by 21.71%and 31.91%.At the genus level,Haliangium has the highest proportion,with a content of 27.64%in the biological sponge iron system,which is 26.58%higher than the ordinary activated sludge system.The dominant bacteria related to nitrogen removal accounted for 43.13%and 57.23%of the common activated sludge and biological sponge iron systems respectively,which provided strong evidence for the better denitrification effect of biological sponge iron system.