The Effects Of Fe²⁺ On Aerobic Biological Denitrification And Its Effect On Microbial Communities

Water pollution and eutrophication have become high-profile global issues.High content of nitrogen and phosphorus nutrient substances in water body is the key cause of eutrophication.Therefor,effective control of urban sewage nitrogen and phosphorus and other nutrient substances discharge is an important way to solve the eutrophication problem.The problem of current urban sewage treatment plant of tail water discharge basic is ammonia nitrogen removal rate is higher,the removal rate of total nitrogen hard to meet the requirements.It is more urgent for the efficient denitrification of municipal wastewater plant and high proportion of phosphorus removal.The technology of combined iron enzymatic activated sludge through the iron ion biochemical reactions involved in microbial metabolism,the iron ion was strengthened to participate in the role of electron transfer and the role of activator enzymatic reaction to enhance the biological activity of metabolic reactions,and to improve biological nitrogen and phosphorus removal efficiency.So the inherent contradictions and bottlenecks of the sewage biological nitrogen and phosphorus removal system could be resolved fundamentally.It provides a new idea for the efficient removal of nitrogen and phosphorus from wastewater.This research adopted the mixed wastewate in the laboratory and simulated sewage treatment process of sewage plant.To examine the sludge domesticated length of SBR system denitrification and phosphorus removal and the effect of COD removal,we can find that the effects of Fe²⁺concentration on denitrification and phosphorus removal in the system and the bioactivity of compound iron enzymatic activated sludge and microbial community metabolism.The conclusions are following:（1）With（25±1）℃,pH=7⁹,DO=3⁵ mg/L,sludge domesticated the length of the SBR system denitrification and phosphorus removal and COD removal have played a role in promoting.When sludge domesticated 15d,the control activated sludge system of ammonia nitrogen removal rate was 75.8%,meanwhile,compound iron enzymatic active sludge system 1(Fe²⁺=1 mg/L)and compound iron enzymatic active sludge system 2(Fe²⁺=2 mg/L)of the ammonia nitrogen removal rate were77.4%and 79.6%respectively.As the time of sludge domestication increased,the removal rate of ammonia nitrogen in each system increased slowly.Continuing to 45 d,the control activated sludge system of ammonia nitrogen removal rate reached 96.2%,the composite iron enzymatic active sludge system 1 and compound iron enzymatic active sludge system 2 ammonia nitrogen removal rate reached 96.9%and 96.9%respectively.And after the sludge domesticated 45d,the COD removal rate in the control activated sludge system,composite iron enzymatic active sludge system 1 and compound iron enzymatic active sludge system 2 compared with 15 d increased by6.8%,3.2%and 6.8%respectively.（2）With the way of disposable iron salt FeSO₄·7H₂O added different concentrations of Fe²⁺to SBR system and study the effect of Fe²⁺concentration on the denitrification of the system.The results showed that the removal rate of nitrogen in the activated sludge system was higher than that of the control activated sludge system,and the removal rate of ammonia nitrogen was increased with the increase of Fe²⁺concentration.At the end of an independent period,the conversion rate of nitrite increased with the increase of Fe²⁺concentration.（3）Fe²⁺has a very important influence on the activity of dehydrogenase and the diversity of microbial communities.Three groups of reaction systems were set up:the control activated sludge system,the activated sludge system with Fe²⁺=10mg/L andFe²⁺=30mg/L.The comparison test of three groups of reaction systems can be sfound:the activity of dehydrogenase of the three systems increased first and peaked at30min.As the aerobic reaction,the microbial activity as a whole is on the decline,but the Fe²⁺=30mg/L dehydrogenase activity of activated sludge system was consistently higher than that of Fe²⁺=10 mg/L of the activated sludge system,Fe²⁺=10 mg/L dehydrogenase activity of activated sludge system was consistently higher than the contrast activated sludge system.The analysis of the microbial community of activated sludge showed that:the Shannon index and Simpson index of Fe²⁺=30mg/L were the highest,with the highest microbial diversity;the Shannon index and Simpson index of the control activated sludge system were the lowest,with the lowest microbial diversity.The ACE and Chao1 index showed that the species richness of Fe²⁺=30mg/L was the highest which was compared to the other two systems.