Study On Enrichment & Denitrification Conditions Of Heterotrophic Nitrifiers & Aerobic Denitrifiers

Nitrogenous wastewater is one of the most important pollutants to the water and the aquatic enviorment. And overdose nitrogen will also cause eutrophication which seriously threat people’s safety. Therefore, the wastewater nitrogen removal has become an urgent problem in the environmental protection field at present. Compared with the physical and chemical methods, the biological denitrification method has many advantages, such as low cost, no secondary pollutions and so on, which makes it receiving much more attention. Especially, the simultaneous nitrification and denitrification (SND) process can not only achieve nitrogen removal at the same conditions and the same reactor, but also shorten the reaction time. However, the enrichment of heterotrophic nitrifiers and aerobic denitrifiers for SND is quite difficult. In this study, basing on the theoretical of SND, using the activated sludge from city sewage treatment plant as inoculums, the heterotrophic nitrobacteria and aerobic denitrifying bacteria were enriched in the constant temperature incubator shaker and a sequencing batch bioreactor (SBR), respectively. And the optimal nitrogen removal conditions were also investigated.The enrichment of heterotrophic nitrifiers and optimal experiment for denitrification conditions were carried out in constant temperature incubator shaker. The experimental results indicated that, the heterophic nitrifiers can be havested in 20 days with the condition of C6H5Na3O7-2H2O as carbon source, NH4Cl as nitrogen source, initial MLSS 3000 mg/L, initial pH 7.3,30℃ and a shaking speed of 210 rpm. The optimal nitrogen removal condition was shaking speed 180-210 rpm, C/N 9:1-11:1, initial MLSS concentration 2500-3000 mg/L, initial pH 6.6-8.2,25-38℃ and culture for 8 h, respectively. And with the optimal condition, the maximum COD, NH4+-N and TN removal rates of 90%,98% and 50% were obtained, respectively. Compared with the original condition, the TN removal rate increased 10%, and the reaction time reduced to 8 h from 24 h. It was found that, expending reaction time, increasing shaking speed and MLSS can improve COD and NH4+-N removal rate; and the effects of environmetal factors on TN removal rate were much obviously.The enrichment of aerobic denitrifers and optimal experiment for denitrification conditions were carried out in a SBR. The experimental results indicated that, the aerobic denitrifers can be harvested in 20 days with the condition of C4H4Na2O4-6H2O as carbon source, NaNO3 as nitrogen source, initial MLSS 3000 mg/L, initial pH 7.0 and DO 5 mg/L. The optimal nitrogen removal condition was aeration time 6 h, DO 3-4 mg/L, C/N 8:1-10:1, initial pH 6.8-7.5, initial MLSS concentration 3500-4000 mg/L, respectively. And with the optimal condition, the maximum COD, NO3--N and TN removal rates of 95%,80% and 68% were observed, respectively. Compared with the original condition, the DO decreased to 3.5 mg/L from 5 mg/L, and the aerobic time reduced to 6 h from 22 h. It was found that, expending aerobic time, increasing MLSS and DO can improve COD removal rate; expending aerobic time, increasing MLSS can improve NO3--N removal rate; and the effects of environmetal factors on TN removal rate were much obviously.