SR0080225 SSNL - Laserfiche WebLink

Home Browse Search

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... Initially, the TN concentrations in the second-stage effluent of all three experiments were above 35 mg/L during the first 5 days(Figure 5a),which indicates a relatively poor nitrogen removal performance at this early stage of the experiments. Possibly,the denitrifying bacteria in the second phase need time to adapt to the new conditions applying after addition of an external carbon source. From day 9 onwards,the TN concentration in the second stage effluent of T2 and T3 decreased,to 34.2 mg/L and 21.9 mg/L respectively. As the experiments continued,this TN concentration in effluent of T3 kept declining,but in T2 it increased again. This indicates that the C/N ratio of 2:1 enhanced the denitrifying capacity of the second stage section to a certain extent by promoting growth of denitrifying bacteria,but it was insufficient to meet the increasing demand of carbon as the denitrifying bacteria proliferated. This is in line with findings reported by Fan et al. [28],who tested a C/N ratio of 2.5 in influent of a constructed wetland which resulted in a TN removal efficiency of only around 25%. On day 17 of the experiments, the TN concentration in the second stage effluent of was more or less stable with mean TN concentrations in the second stage effluent of 48.4 mg/L(giving a 19.6%removal rate)in Tl,41.0 mg/L(31.8%removal rate)in T2 and 14.7 mg/L(75.4%removal rate)in T3. The TN removal rate of the second stage effluent had thus nearly doubled in T2 compared to T1,but the resulting concentration was still too high to meet the national sewage discharge B standard(GB 18918- 2002)(TN:5 20 mg/L). The second-stage effluent of T3 passed this standard, and even passed the sewage discharge a standard(TN:5 15 mg/L). The TN removal of T3 had improved by compared to I. This clearly shows that addition of a carbon source in the second stage influent enhanced the nitrogen removal efficiency of the system,whereby a C/N ratio of 5 performed better than a ratio of 2. The best TN performance obtained resulted in"-79.8%removal of TNS 3.3. Effect of C/N Ratio on Removal Efficiency of Chemical Oxygen Demand The COD concentration of the first stage influent was 268.3 f 20.0 mg/L. This reduced during the first stage to 22.8 mg/L, 24.5 mg/L and 20.5 mg/L for effluent of T1,T2 and T3 respectively, so the mean fraction of removed COD reached up to 90% in all three experiments. However, the mean concentration of NO3 -N in the first stage effluent remained above 48.3 mg/L, resulting in a C/N ratio in the first stage effluent below 1. The effect of increasing this ratio to 2 and 5 in T2 and T3, respectively,on COD removal is shown in Figure 6. Whereas the mean concentration of COD in the second stage effluent of T 1 decreased to only 16.2 mg/L, for T2 and T3 it went down to 9.3 mg/L and 8.7 mg/L respectively. Compared with Tl,the mean COD concentration in the second stage effluent of T2 and T3 were much lower,indicating that the addition of glucose to the second stage influent had not resulted in an increase of COD in the effluent,but rather promoted the removal of COD during the second stage. Clearly,this external carbon source enhanced the activity and growth of denitrifying bacteria. The amount of glucose required for this was not fully met under experimental condition T2,as the best COD removal was obtained with T3,which received the highest amount of glucose. In another study,Chen et al. [7] found that the removal efficiency of COD could reach up to 85%in the nitrifying section of CRI,while Wang et al. [20] determined an optimal C/N ratio for denitrification of 6-7 when they used glucose as external carbon source. Zhang[29] noticed that nitrogen could be completely removed in SBR by adjusting the C/N ratio to 7.1 with added glucose. Yan et al. [30] reported that if the main purpose of the sewage treatment was to remove nitrogen, the C/N ratio in influent should be slightly lower than the optimum C/N ratio,which could not only guarantee high COD removal rates (resulting in low residual organic matter),but also produce a better nitrogen removal performance. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6069465/ 11/18