Study On Performance And Microbial Community In The Combined Micro-electrolysis,Heterotrophic And Autotrophic Denitrification(CEHAD)

Nitrate(NO3--N)had been recognized as one of the most ubiquitous chemical contaminant in aquifers,however it is difficult to remove nitrate from N-contaminated water with low C/N ratios,due to a large amount of organic carbon consumed in the heterotrophic denitrification.Groudwater protection and treatment is a significant issue,because it related to ecological security and people's health.In this study,based on iron-carbon micro-electrolysis carriers,a combined micro-electrolysis,heterotrophic and autotrophic denitrification(CEHAD)was developed for highly efficient nitrate removal from synthetic groundwater with a low C/N.This study focued on continuous operation and the effect of different parameters on the CEHAD process,using the influent with NO3-N 40 mg/L and COD 20 mg/L(C/N=0.5).High-throughput sequencing technology was used to analyze the microbial community and diversity,and kinetics of nitrate degradation in the CEHAD was explored.The results showed that:(1)The CEHAD operation was continuously performed for 314 days,and divided into 3 stages according to different conditions.In the stage without pH control,pH in effluents of the reactor reached to higher than 9.5,which could have significant negative impacts on biological denitrification.As expected,the total nitrogen(TN)removal efficiency was only 46.8±3.0%.In the stage adjusting pH with diluted HC1,the optimal nirate and TN removal efficiencies were 95.7%± 1.6%and 90.1%±2.4%,respectively.To further optimize the CEHAD process with the concept of carbon emission reduction,CO2 was added to adjust pH in the reactor in the next stage,and the optimal nirate and TN removal efficiencies were 98.8%±0.4%and 95.6%±1.9%,respectively.The CEHAD process achieved highly efficient denitrification with either HCl control or CO2 control.Its best performance results showed that the nitrate concentration in groundwater can be reduced from that in class ? to class ? in the standard GB/T 14848-2017.(2)Many microorganisms which were similar to reported heterotrophic and autotrophic denitrification microorganisms were found in the reactor,include Thiobacillus?Comamonas?Thermomonas?Hydrogenophaga?Denitratisoma,a denitrification microbial community was established.However in the stage adjusting pH with CO2,many microorganisms related to methane metabolism like Anaerolineaceae and Methylocystis were found,which means the addition of C02 affect the carbon metabolism in the reactor.(3)In the temperature of 30?,the degradation of nitrate was first order order reaction and the model based on Monod kinetics were established and fit well.However when the temperature drops to 15?,the degradation of nitrate is significantly inhibited,degradation model was zero order order reaction and did not accord with the Monod kinetic equation.