Study On The Performance Of Iron Carbon Microelectrolysis And Iron Oxide Coupling Biological Denitrification

Water nitrogen pollution has become a global pollution problem.Although the traditional biological nitrogen removal technology has good nitrogen removal efficiency and is easy to operate,it has problems of high operating cost and large burden of follow-up sludge treatment and disposal.Therefore,it is urgent to seek some environment-friendly,product-efficient and economically efficient technical means to solve these problems.The combined nitrogen removal process of iron carbon micro-electrolysis and biological method has become a research hotspot in the field of sewage treatment.Iron oxides can also affect the metabolism and activity of microorganisms to a certain extent.Therefore,the study of iron carbon micro-electrolysis and iron oxide coupled biological denitrification for nitrogen removal has important practical significance for solving the problem of urban wastewater treatment with low carbon nitrogen ratio in China.In this study,the dosage of iron and carbon with the best chemical reaction effect was first selected through single factor test.When the initial concentration of NO₃^--Nwas 30 mg/L,pH=6,iron-carbon ratio was 2:1,and the dosage of iron was 4 g,The removal rate of NO₃^--N by iron-carbon microelectrolysis was 65.46%.On the basis of optimizing the operation conditions of the process,the granular（T1）and powder（T2）fillers without adding iron oxide,the granular（T3）and the granular（T4）fillers with adding iron oxide were prepared respectively.The nitrogen removal process and characteristics of the nitrogen containing wastewater treated by iron-carbon micro-electrolysis process with different fillers were analyzed in depth.The results of batch experiments show that most of NO₃^--N involved in the reaction in the system is reduced to NH4+-N,and the total nitrogen treatment effect of the filler without iron oxide is better than that of the filler with iron oxide.These four kinds of micro-electrolytic fillers have almost no removal effect on COD.In order to further explore the relationship between nitrogen removal and microorganisms and iron-carbon fillers,an experimental system was established to run activated sludge nitrogen removal alone and add four kinds of iron-carbon micro-electrolytic fillers coupled with biological denitrification nitrogen removal respectively.Batch experiments were conducted on the above systems,and the effects of Fe-C micro-electrolysis coupling biological nitrogen removal at different initial NO₃^--N concentrations（30,60,80mg/L）were respectively investigated under the conditions of carbon to nitrogen ratio of 5:1and 3:1.Activated sludge alone can degrade NO₃^--N faster,but a large amount of NO₂^--N generated will accumulate and inhibit denitrification.After the addition of micro-electrolytic fillers,the accumulation of NO₃^--N is significantly reduced,and when the added organic carbon source is exhausted,microorganisms can still use the electrons generated by iron carbon micro-electrolysis for denitrification,so that the denitrification reaction is complete.The filler added with Fe₃O₄can promote the growth and metabolism of microorganisms because of its good conductivity and can act as an electron donor.However,Fe₂O₃is non-conductive,which will hinder the release and stable output of iron-carbon micro-electrolysis electrons,and inhibit the iron-carbon micro-electrolysis coupling biological nitrogen removal system.Accordingly,Fe₃O₄experimental group had the best effect,Fe₂O₃experimental group was worse.Compared with the iron-carbon micro-electrolytic chemical nitrogen removal system,the coupled biological nitrogen removal system can greatly improve the removal of COD,which is mainly due to the metabolic action of microorganisms.The low C/N condition is better than the conventional C/N condition to reflect the superiority of the iron carbon micro-electrolysis coupled biological nitrogen removal system to remove nitrogen and COD after adding fillers.In the long-term SBR reactor test,the B reactor with the addition of iron-carbon micro-electrolytic filler at a low C/N（3:1）showed a better nitrogen removal effect than the A reactor without the addition of filler:after 90 days,the NO₃^--N removal rate of the B reactor was 88.14%and that of the A reactor was 74.36%.After 90 days,the removal rate of TN in B reactor is 87.34%,and that in A reactor is 67.27%.The two reactors have little difference in COD degradation effect.The addition of iron-carbon fillers has many effects on activated sludge,including:（1）The sedimentation performance of activated sludge was enhanced,and the iron ions released by iron-carbon micro-electrolysis increased the activated sludge EPS mainly by stimulating the microbial synthesis of protein,so that the dense EPS（T-EPS）content of reactor B（123.63 mg/g VSS）was significantly higher than that of reactor A（98.49mg/g VSS）.（2）When the sludge form was changed,the sludge floc aggregation was more obvious in the B reactor with filler added.After the operation,a large number of microorganisms were attached to the surface of the filler,and it could maintain a good morphological structure.（3）Under the enhanced effect of iron-carbon micro-electrolysis,the microbial community structure in activated sludge has changed,and there are many unknown strains,and the diversity of community structure in the iron-carbon micro-electrolysis coupled biological nitrogen removal system needs further research.