Study On The Effect Of Iron-Carbon Microelectrolysis On Biological Denitrification Of Low Carbon To Nitrogen Ratio Wastewater

The traditional denitrification process with organics as electron donors has high nitrogen removal efficiency but high investment cost.The disposal of low C/N wastewater has always been a difficult and hot spot in the field of water treatment research.In the low C/N environment,organics cannot supply enough electrons to the activated sludge for thorough denitrification.So,it is necessary to study how to improve the electron supply in denitrification process.In this study,based on denitrifying activated sludge cultured in UASB reactor,iron carbon micro-electrolysis reaction was coupled with biological denitrification to achieve a high denitrification rate under low C/N conditions.The iron-carbon ratio,pH,temperature,inorganic ion concentration and reaction time were compared to investigate the applicability of iron-carbon micro-electrolysis to microbial denitrification under different environmental conditions.The microbial diversity and population structure of the composite system of Fe-C microelectrolysis coupled microorganisms were analyzed.The conclusions of this study are as follows:?1?According to the feasibility study of biological denitrification promoted by adding iron-carbon,Fe-activated carbon can play a good role in promoting the original denitrification system,and the addition of iron-carbon reduces the dependence of microorganisms on carbon sources in the denitrification process.Under the condition of C/N=3,compared with adding activated sludge alone,the removal rate of NO₃^--N increased from 52.1%to 83.3%after adding Fe-activated carbon,and the concentration of NO₃^--N decreased by 14.08mg·L^-11 in the same time.By Comparison between the addition of elemental iron and activated carbon,this effect is not a simple superposition.?2?The mass of the iron was fixed and the added mass ratio of iron to carbon were controlled.Under the condition of C/N=2.25,the comparative experiments of iron-carbon ratios of 1:1,2:1,3:1,4:1 and 5:1 were carried out.The results showed that the denitrification efficiency was the highest when the iron-carbon ratio was 1:1.Compared with denitrifying sludge,the removal rate of NO₃^--N increased from41.99%to 93.84%.At the same time,with the increase of iron-carbon ratio,ammonia nitrogen production in the composite system also increased.?3?Under the condition of 10??low temperature?,25??room temperature?,35??high temperature?comparative experiments were carried out,the results demonstrated that iron-carbon micro electrolysis at 25?and 35?had similar promoting effects.Under the condition of low temperature,promoting effect is not obvious.Due to the role of iron-carbon micro-electrolysis,the traditional denitrifying activated sludge can achieve similar denitrification results without high temperature conditions.?4?The influence of pH value on the denitrification effect of Fe-activated carbon-denitrifying sludge was studied,and comparative experiments with initial pH values of 5,7,9 and 11 were conducted.The results showed that the nitrogen removal effect was the best when the pH value was 7,and there were no significant difference in denitrification effect when the pH values were 5,9 and 11 respectively,but more ammonia nitrogen was produced when the pH value was 5.pH value has little effect on the denitrification rate of Fe-activated carbon-denitrifying sludge complex system,but it will affect the production of ammonia nitrogen.?5?The influence of NH₄⁺and Fe²⁺on the composite system was studied by adding them into the system.The study showed that the reaction rate of the composite system decreased with the increase of NH₄⁺concentration.The addition of Fe²⁺can increase the removal rate and reaction rate of NO₃^--N,but too high Fe²⁺concentration will increase the production of ammonia nitrogen in the system.?6?Consecutive four-period experiments were carried out for the composite system with different iron-carbon ratios.After the four-period experiments,the experimental groups with iron-carbon ratios of 1:1 and 2:1 still maintained a good promoting effect,while the promoting effect of iron-carbon ratios of 3:1,4:1 and 5:1showed different degrees of attenuation.?7?High-throughput sequencing of microbial samples was conducted in the process of experiments,the results showed that adding the iron-carbon affected the microorganism composition in the traditional biological nitrogen removal system,after adding the iron-carbon in the samples,the content of Proteobacteria,Gammaproteobacteria,Betaproteobacteriales and Thauera increased relatively to the sludge samples,In the samples with iron-carbon ratio of 5:1,the content of Arenimonas is higher than other samples.