| Nitrogen heterocyclic compounds(NHCs) have strong toxicity. If the industrial wastewater containing NHCs has not been effectively treated and discharged into the environment, it is bound to cause serious pollution to natural environment. The wastewater containing NHCs is treated usually by the nitrification-denitrification process. However, when the content of NH4+-N in wastewater is lower, NOx--N is also lower in nitrification reflux liquid and the influent COD/NOx--N is high in denitrification section, that results in the decrease of organics removal rate. Therefore, this paper focused on the efficient degradation of NHCs by the nitrification-denitrification process at high COD/NOx--N. The traditional anoxic denitrification section was converted into anaerobic simultaneous(shortcut) denitrification and methanogenesis. NHCs that were not be degraded by shortcut denitrification were consumed by anaerobic methanogenesis. Organic content, OLR and energy consumption were decreased in nitrification section, and bioenergy produced by anaerobic digestion of NHCs was obtained.In this paper, anoxic and anaerobic processes were studied in the fornt of aerobic nitrification section. Quinoline, pyridine and indole of typical NHCs were selected as research objects. Their degradation characteristics were investigated in systems of shortcut denitrification, anaerobic methanogenesis and anaerobic simultaneous(shortcut) denitrification and methanogenesis respectively. The main research conclusions are as follows:1. In systems of shortcut denitrification and anaerobic methanogenesis, degradation processes of NHCs were both divided into adsorption, adaptation and degradation stages. NHCs had inhibitory effects on microbial activity, that resulted in the extension of adaptation stage with the increase of initial NHCs concentration. Compared with shortcut denitrification, the adaptive duration of anaerobic methanogenesis was about 20~30 times of that.2. The inhibitory intensity of NHCs on microbial activity directly reflected in the length of adaptation stage, and also indirectly reflected in the inhibitory ratio of bio-enzyme activity. Inhibitory ratios of four bio-enzyme activities were all maximum at the end of adsorption stage, and maximum inhibitory ratios rose up with the increase of initial NHCs concentration. After the adaptation stage, four bio-enzyme activities all restored to initial levels in the shortcut denitrification system, but one or more bio-enzyme activities did not restore in the anaerobic methanogenesis system. Toxicity effects of NHCs on anaerobic methanogens were stronger than that on denitrification bacteria.3. In systems of shortcut denitrification and anaerobic methanogenesis, based on the length of adaptation stage, maximum inhibitory ratios of conventional bio-enzyme activities and characteristic bio-enzyme activities(nitrite reductase and coenzyme F420) at the degradation stage, it was inferred that the toxicity order was quinoline > indole > pyridine, and the order of reaction rate was pyridine > indole > quinoline for three NHCs.4. In the shortcut denitrification system, the optimum COD/NO2--N were 4, 8 and 6 respectively for quinoline, pyridine and indole. At the optimum COD/NO2--N, substrate removal rates were close to 100% and denitrification reaction was complete. When the influent COD/NO2--N was higher than the optimum, carbon source remained, and on the contrary nitrogen source remained. In the anaerobic methanogenesis system, organic substrate removal rate was close to 100% when the reaction time was enough. The order of methane yield rate was pyridine > indole > quinoline, and corresponding methane yield coefficient were 0.234, 0.250 and 0.163 m L/mg COD.5. For the shortcut denitrification system at high COD/NO2--N, the bacterial diversity was more abundant for quinoline and the bacterial population was more for pyridine, and dominant bacterial genera included Bellilinea sp. and Alicycliphilus sp.. For the anaerobic methanogenesis system at high NHCs concentration, the bacterial diversity was more abundant for indole and the bacterial population was more for pyridine, and dominant bacterial genera included Exilispira sp., Longilinea sp. and Desulfomicrobium sp.; The archaea diversity and population was more abundant for pyridine, and dominant archaea genera attached to methanogens of Euryarchaeota. Functional genes of two systems were quantitatively analysed by Q-PCR, and copy numbers of denitrification genes(nir K, nir S and nos Z) and mcr A gene were more for pyridine.6. NHCs could be degraded efficiently by alone shortcut denitrification or anaerobic methanogenesis system, but there were deficiencies for two systems. For shortcut denitrification, when the influent COD/NO2--N was high, denitrification reaction was incomplete and lots of carbon source remained, that resulted in the decrease of organics removal rate; For anaerobic methanogenesis, when the influent NHCs concentration was high, microbial activity was strongly inhibited, that resulted in the decrease of reaction efficiency and the extension of reaction time.7. The quinoline wastewater was treated by the UBF reactor with the function of anaerobic simultaneous(shortcut) denitrification and methanogenesis. At high COD/NO2--N, the treatment effect of this reactor was very stable, and total removal rates of quinoline and NO2--N were 88.83% and 99% respectively. The treatment effect of the UBF reactor was obviously better than alone shortcut denitrification or anaerobic methanogenesis system. Optimal operating conditions of the UBF reactor were SRT=30d, HRT=4h and p H0=7.5.8. Based on analyses of characteristic bio-enzymes and functional gene numbers, denitrification bacteria were mainly concentrated in the lower part of the reactor, and anaerobic methanogens were mainly concentrated in the middle and upper part of the reactor, while two kinds of microorganisms existed in the middle and lower part of the reactor. The flora structure in the coexistence state was analysed by high-throughput sequencing. Dominant bacterial genera included Longilinea sp., Comamonas sp., Thauera sp., Bellilinea sp. and Solitalea sp., which had functions of denitrification, anaerobic hydrolysis and acidification; Dominant archaea genera included Methanosaeta sp., Methanoregula sp. and Methanobacterium sp., which attached to methanogens of Euryarchaeota.9. There was the phenomenon of VFAs accumulation in the UBF reactor. TVFA rose first and then dropped from the bottom to up of this reactor. TVFA/COD was 25.60% in the effluent, and it was indicated that methanogenesis reaction was complete.10. p H rose first then dropped and then rose from the bottom to up of the UBF reactor. p H changed between 6.57~7.65 and was basically in the appropriate p H range of corresponding microbes(denitrifying bacteria, fermenting and acid producing bacteria, methanogens). BAlk dropped first and then rose from the bottom to up of this reactor. BAlk changed between 2076~2500 mg Ca CO3/L and had good p H buffer capacity. ORP dropped gradually from the bottom to up of this reactor. ORP changed from-120 to-413.3 m V, from anoxic environment suitable for denitrifying bacteria to anaerobic environment suitable for fermenting and acid producing bacteria, then to anaerobic environment suitable for methanogens.11. The biogas composed of CH4, CO2, H2 and nitrogen gas in the UBF reactor, and their average percentages were 54.41%, 44.09%, 0.58% and 0.92% respectively. Average daily productions of CH4 and nitrogen gas were 4.34 and 0.96 L/d respectively.12. YC and M were 0.49 and 37.24% repectively in the UBF reactor. YC and M of this reactor were higher and lower repectively than that of anaerobic methanogenesis for quinoline.13. With the increase of influent quinoline concentration, the shock effect of OLR on denitrifying bacteria was not strong, but the shock effect of OLR on anaerobic methanogens was strong. At high OLR(> 4.89 g COD/L/d), the quinoline removal rate of the UBF reactor decreased. |
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