Study On The Effect Of Additional Iron Sources On Nitrogen Removal And Microbial Diversity In Low Carbon And Nitrogen Ratio Wastewater Treatment Systems

At present,China's water pollution is serious,water resources shortages and other water environmental problems are significant.It is imminent to create a good and livable ecological environment and build a socialist ecological civilization.Nitrogen is a major pollutant in wastewater,but its research is still poor on nitrogen removal,especially high-nitrogen wastewater.The removal of high-nitrogen wastewater is still a research hotspot.The traditional method of nitrogen removal is not suitable for high-nitrogen wastewater.The lack of carbon source is an urgent problem to be solved in the current treatment of high nitrogen.Short-range denitrification and anaerobic ammonium oxidation can reduce the demand for organic carbon sources in the denitrification process.Because the process conditions are demanding and pretreatment is required to stabilize the treatment system,the main way to solve the high nitrogen wastewater is to manually add carbon sources,so that the carbon to nitrogen ratio can meet the needs of the normal denitrification process,but this method will greatly increase the treatment cost of the sewage plant.By adding a small amount of iron source to promote the biological nitrogen removal process,combined with the existing treatment methods,the treatment requirements of high-nitrogen wastewater can be better achieved.And the ferrous salt has are inexpensive,which can reduce the carbon source.This experiment uses SBR reactor,combined with small test and continuity test,through the detection of water ammonia nitrogen concentration,total nitrogen concentration,activated sludge dehydrogenase activity and microbial diversity combined with sludge morphological changes and other indicators,analysis the effect of additional iron ource of on biological nitrogen removal.The pilot test is divided into two parts:the carbon-nitrogen ratio of 0.5 and 2.2.Under different carbon-nitrogen ratio conditions,the dosage and type of the additional iron source are studied by a single addition of different concentrations and different types of external iron sources.The effect of nitrogen,and through experiments to study the difference in the effect of the addition of iron source under different carbon-nitrogen ratio conditions.The continuity test is based on the results of the pilot test.The continuous test adds Fe³⁺for a long time,and adjusts the influent carbon to nitrogen ratio.Combined with the total nitrogen concentration of the effluent,microbial diversity and activated sludge morphology to study the influence of the internal microorganisms on the mechanism of Fe³⁺on biological nitrogen removal.The conclusions of this study are as follows:?1?Different types of iron sources promoted the denitrification process,and showed low concentration promotion and high concentration inhibition.There was no significant difference in the effect of single addition of Fe³⁺and Fe³⁺.But the two effects The effect is better than iron powder,and the single-feed iron source promotes the nitrification reaction better than the denitrification reaction.?2?In the SBR system with low carbon to nitrogen ratio,the effect of nitrogen removal was the best when Fe³⁺was added in a single dose of 2 mg·L^-1.The ammonia nitrogen removal rate can reach 93.98%;the total nitrogen removal rate is 45.22%,which is 8.77%higher than the blank control group.When the single dose was 20 mg·L^-1,the system nitrogen removal was inhibited.?3?The continuous addition of Fe³⁺promotes the progress of SBR nitrification,and this effect is rapid.The presence of iron can maintain the ammonia nitrogen removal rate above 95.52%.When the iron source is stopped from being added to the system,the removal rate of ammonia nitrogen drops immediately,and the recovery rate of the recovered iron source will immediately rise.Fe³⁺gives the sludge a strong anti-shock load capacity,and the system does not have the ammonia nitrogen concentration due to the influent.The change is affected,which solves the problem that the traditional activated sludge disintegrates in the excessive impact load and causes the nitrification reaction to be poor.?4?The accumulation of iron promotes the denitrification reaction.Under the long-term addition of Fe³⁺,the total nitrogen removal rate can reach 90.69%,which is 40.59%higher than that when no iron salt is added.When the iron source is stopped,the total nitrogen removal rate will gradually decrease,and the removal rate will gradually increase after the addition of the iron source.It indicates that the accumulation of iron promotes the denitrification reaction.?5?The effect of external iron source on the denitrification reaction of the system decreases with the increase of carbon to nitrogen ratio.And the promotion of Fe³⁺is more significant at low C/N.The promotion effect of single-feed iron source is not enough to completely solve the problem caused by insufficient carbon source.The overall nitrogen removal effect of the system is still poor,and the combined effect of carbon source and iron source is still needed in practical application.?6?Addition of Fe³⁺can significantly increase the microbial activity.The addition of iron salt makes the TTC-DHA grow steadily which characterizes the microbial activity in the activated sludge,from 7.80?g/?mg?h?to 59.21?g/?mg?h?.When stop the addition of iron source the TTC-DHA will be significantly reduced.?7?Fe addition ³⁺has an effect on microbial diversity and species abundance in SBR systems,especially for nitrifying bacteria,denitrifying bacteria and polyphosphate bacteria,which are closely related to nitrogen and phosphorus removal.It helps the strains related to nitrogen and phosphorus removal in activated sludge to become the dominant species,thus improving the effect of nitrogen and phosphorus removal.The number of PHOS-HE51 and Xanthomonadales_Incertae_Sedi,which are closely related to phosphorus removal,are significantly increased in the anaerobics family involved in biological nitrogen removal.After stopping the addition of iron source,although the abundance and number of microbial species in the system did not change significantly,the number of dominant species such as nitrifying bacteria,denitrifying bacteria and polyphosphate bacteria increased significantly.?8?The presence and accumulation of iron increases the activated sludge particles,increases the sludge concentration,and enhances the impact load resistance,which is beneficial to improve the structural strength and stability of the activated sludge.With the addition of the iron source,the sludge particles increase,the protozoa multiply,and the structural strength of the activated sludge increases.So that it can improve the stability of the SBR system.