Study On Filamentous Bulking And Control During Biological Nitrogen Removal From Domestic Wastewater

At present, many city’s sewage is low C/N, which has a bad impact on thenitrogen removal.SND and short-cut nitrification were new efficient, economic,energy-saving biological nitrogen removal technique，which can be gradually realizedunder low DO and can improve the nitrogen removal. However, low DO can easilycause the sludge bulking，As key problems to be solved, complex sludge bulkingunder low DO need be studied in depth.In this study, by treating real domestic sewage which is low C/N in A/Oprocess，the nitrogen removal effect was investigated under different parameterconditions without external carbon source firstly. On this basis, the nitrogen removaleffect and further development of viscous sludge bulking were investigated underhigh C/N condition by putting external carbon sources into the real domestic sewage，finally, the effluent met the national level A emission standard. Then the starting offilamentous bulking under low dissolved oxygen and the pollutant removal andmigration of strains in the process of filamentous bulking to malignant bulking underlow dissolved oxygen were investigated systematically in A/O process. At last， thecontrol of the malignant bulking in SBR and A/O process were studied.By treating real domestic sewage which is low C/N in A/O process， theaverage removal rates of NH4+-N、TN and COD were100%、49.48%and82.03%respectively under the better operating parameter without external carbon source. Onthis basis, then the system reached the best operating parameter by putting externalcarbon sources into the real domestic sewage. Finally, average NH4+-N, TN and CODin effluent met the national level A emission standard，SVI was also relatively stableat about200ml/g.The starting of filamentous bulking under low dissolved oxygen and the wholeprocess of filamentous bulking to malignant bulking under low dissolved oxygen wereinvestigated systematically in A/O process. Results showed that in the early，SVIvalues increased and could be maintained under250mL/g when the dissolved oxygenvalue was0.5mg/L, which was in line with the characteristics of limited filamentousbulking under low dissolved oxygen basically. In this period, average removal rates ofCOD and TN were improved by2.23%and7.75%respectively compared to the high dissolved oxygen stage. H.hydrossis is the dominant filamentous bacteria in bulkingsludge in the system. Network structure of twining filamentous bacteria played afiltering role, SS in the effluent was almost0. However, this state did not maintain,the SVI climbed to500mL/g nearly after some days and malignant bulking occuredwhen the system conditions remained same. Compared to the system in the early stage,removal rates of NH4+-N、COD and TN decreased.The result of FISH manifestedthat the main filamentous bacteria that led to bulking was also H.hydrossis.The number of baffles in aerobic zone and dissolved oxygen were increasedto1mg/L respectively to control the malignant bulking in A/O process，results showedthat SVI values declined to350~310mL/g and kept steady. Average removal rate ofTN was84.52%，improved by32.36%compared to52.16%in the malignant bulkingstage. In the later stage of experiment, the average removal rate of NH4+-N kept100%mostly，improved by37.52%compared to62.48%in the malignant bulkingstage, the removal efficiency of COD was81.86%. At last NH4+-N、TN and COD inthe effluent both reached the national level A emission standard.On this basis，dissolved oxygen were increased to2mg/L，then SVI valuesdeclined，finally the SVI values kept under150mL/g and sludge bulking wascontrolled. H owever，removal rate of TN declined to40.84%from89.57%，finallythe TN in the effluent was close to40mg/Land the effluent quality deteriorated.In SBR process， the effect of controlling filamentous sludge bulking whichhappened when the dissolved oxygen value was0.5mg/L in A/O process and thedominant filamentous bacteria was Haliscomenobacter hydrossis with differentoperation patterns were investigated by treating real domestic sewage which is lowC/N. Results showed that, during A/O pattern in SBR process, SVI value hasmaintained beyond300ml/g when organic loading (F/M) was0.83kg/(kg d)with the dissolved oxygen value was about2mg/L, the sludge bulking could not beeffectively controlled. The result of FISH manifested that the main filamentousbacteria was also H.hydrossis filamentous bacteria. In this period, average removalrates of TN and COD were31.17%and65.04%respectively.In SBR process during aerobic pattern,when organic loading (F/M) was0.37kg/(kg d),the dissolved oxygen value was also about2mg/L,the sludge bulkinghas been controlled effectively and SVI value has remained below150ml/g. In thisstage, the removal rate of NH4+-N reached100%nearly，the NH4+-N in effluent was almost0mg/L.Average removal rate of TN and COD improved to70.70%and73.90%respectively. The average TN and COD in effluent were18.40mg/L and46.90mg/L respectively which were close to the national level A emission standard.