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4/2/2019 Effect of C/N Ratio on the Removal of Nitrogen and Microbial Characteristics in the Water Saturated Denitrifying Section of a Two-Stage C... <br /> 80 320 <br /> T <br /> 70 \T T T <br /> --� T T T/TAT 280 <br /> r <br /> 60T <br /> � <br /> � i ,7 <br /> y t ,t I 240 v <br /> 50 —�— _ <br /> COD in efiluent of"I'1 (control) <br /> U #— ('01) in effluent of T2 (C:N=2:1 ) = <br /> 40 A COD in effluent ul"13 (C:N=5:1 ) 200 <br /> o —v—COD in influent <br /> 30 L <br /> = 160 <br /> 20 J <br /> 0 0 <br /> U J <br /> 120 <br /> O 10 1 1 1 - O <br /> U 1 U <br /> 0 80 <br /> 0 5 10 15 20 25 30 35 40 45 50 <br /> Time (c)) <br /> Figure 6 <br /> The chemical oxygen demand(COD)concentration in influent of the first stage and in effluent of the <br /> second stage of the three experimental setups. <br /> 3.4. Analysis of the Microbial Communities and EPS <br /> The bacteria in the water-saturated denitrifying section were quantitatively analyzed by the MPN <br /> method(Figure 7). The sand from the second stage of T1 contained 6.5 x 103 CFU(g sand)—] <br /> nitrifying bacteria,and approximately half were present in the sand of T2 and T3 (3.3 x 103 and 3.1 x <br /> 103 CFU-(g sand) I,respectively). The low amount of dissolved oxygen and NH4+-N in the fully <br /> submerged second stage most probably limited the growth of these aerobic bacteria [31]. These <br /> relatively low counts of nitrifying bacteria support the conclusion that the nitrification reaction was <br /> restricted in the fully submerged phase of the CRI. A previous study [32] described that when organic <br /> matter was abundant in sewage,heterotrophic bacteria could grow rapidly and these would outcompete <br /> nitrifying bacteria for dissolved oxygen and nutrients. <br /> https://www.ncbi.nIm.nih.gov/pmc/articles/PMC6069465/ 12/18 <br />