Nitrous Oxide Emission During Nitrification For Nitrifiers With Different Growth Strategies

Nitrifiers with different growth strategies could be enriched with different ammonia nitrogen concentrations and different operating modes. The N2O release characteristics was studied under different operating modes, different initial concentrations of ammonia and nitrite. The main cause and process responsible for N2O emission during nitrification was analyzed under different conditions with the addition of various inhibitors. The study aimed to illustrate the release mechanism of N2O during the nitrification process and control greenhouse gas emissions during wastewater treatment.The synthetic wastewater included:NaAC:125mg/L, NH4-N:60mg/L or180mg/L, NaHCO3;1g/L or2.8g/L. Hydraulic retention time of four reactors were all12h; sludge retention time was around20d. A cycle of SBR reactor was4h, with feeding of10min, aeration for3h (including inflow of water), settlement for35min, and withdraw and idle of25min.The FISH esperiment results showed that the ammonia oxidizing bacteria with different growth strategies were enriched from different operating modes. The dominating AOB in SBR reactor was Nitro.somonas oligotropha lineage with r-growth strategy, and that from the contiouous reactor was Nitrosospira spp. with K-growth strategy.The results of outflow water concentrations during the operation of the water showed that after60days’domestication, nitration process performance of the four reactors were good with stable running, water of outflow was detected without ammonia nitrogen or nitrite, NH4+-N removal rates were all above99.0%. Dynamics of Ammonia Oxidizing Bacteria was tested in order to obtain different nitration kinetic parameters. For activated sludge from low nitrogen SBR reactor, subsaturation constant K was2.41mg/L, maxmium of reaction rate r was51.02mgN/gVSS/h. For activated sludge from high nitrogen SBR reactor, subsaturation constant K was6.75mg/L, maxmium of reaction rate r was83.33mgN/gVSS/h, and for activated sludge from low nitrogen flow reactor, subsaturation constant K was0.24mg/L, maxmium of reaction rate r was18.42mgN/gVSS/h, for activated sludge from high nitrogen flow reactor, subsaturation constant K was0.31mg/L, maxmium of reaction rate r was31.06mgN/gVSS/h.The results of operation cycle showed that N2O was generated during nitrifying process. SBR-60reactor had an accumulative amount of1.8076mg/L, SBR-180reactor was1.4077mg/L, CON-60reactor was0.0050mg/L, and CON-180reactor was0.0281mg/L. Account the initial concentration of ammonia for3.01%,0.78%,0.007%and0.015%respectively. The release of N2O could be affected in the different run modes. The accumulated concentration of N2O released from continuous operating mode was much less than that released from SBR mode.The N2O concentrations generated from reactors increased with the increase of initial concentration of ammonia nitrogen of the inflow water. The N2O concentrations accounted the concentrations of reacted ammonia nitrogen for0.64%-2.32%,0.15%-0.55%,0.51%-1.40%and0.29%-1.27%respectively. The N2O release ratio had good linear relationship with initial ammonia concentration, SBR-60:rN2O-N/NH4-N=0.045CNH4-N-0.16(R2=0.99), SBR-180: rN2O-N/NH4-N=0.01CNH4-N-0.052(R2=0.99), CON-60: rN2O-N/NH4-N=0.02CNH4-N+0.34(R2=0.85), CON-180:rN2O-N/NH4-N=0.02CNH4-N+0.05(R2=0.99). The different initial nitrite tests showed that the N2O generated from reactors increased with the increase of initial concentration of nitrite nitrogen. The N2O concentrations accounted the concentration of reacted ammonia nitrogen for1.67%-4.02%,0.89%-3.22%,1.38%-3.78%and1.16%-5.81%respectively. The N2O release ratio had good linear relationship with initial nitrite concentration. SBR-60rN2O-N/NH4-N=0.087CNO2-n+1.377(R2=0.97), SBR-180: rN2O-N/NH4-N=0.078CNO2-N+0.0593(R2=0.97), CON-60:rN2O-N/NH4-N=0.12CNO2-N+1.48(R2=0.99), CON-180:rN2O-N/NH4-N=0.24CNO2-N+1.19(R2=0.99).The results of N2O release test under different initial substrates and different nitrification inhibitors showed that the main cause of N2O release was the nitrifying bacteria biological’s effect especially in the ammonia oxidation process. The hydroxylamine’s effect played an important role in the generation of N2O; the presence of nitrite promoted the generation of N2O...