Study On Endogenous Denitrification Of Gaos For Enhanced Drbc Denitrification And Low Energy Consumption Wastewater Treatment

At present,decentralized sewage that is difficult to be centrally treated in China causes harm to the environmental quality of urban and rural living areas.Small-scale decentralized sewage treatment has considerable room for improvement.As one of the biofilm methods,rotating biological contactor(RBC)or drum-rotating biological contactor(DRBC)is suitable for small-scale distributed water treatment due to its advantages of small area,strong impact resistance,no sludge swelling and low sludge yield.However,the traditional DRBC process has poor nitrogen removal ability,so it is difficult to be applied to the field requiring high total nitrogen(TN)emission.The purpose of this project is to construct high abundance glycogen accumulating organisms(GAOs)biofilms in DRBC system,and further coupling zeolite granular materials,to achieve low energy consumption wastewater treatment technology based on GAOs endogenous denitrification enhanced biological nitrogen removal.In this paper,the effects of sequential batch feeding on GAOs enrichment and TN removal efficiency of DRBC at conventional rotating speed were investigated.Secondly,the enrichment mechanism of GAOs and the start-up and operation of DRBC reactor under the condition of low rotational speed were studied on the basis of sequential batch feeding mode.Finally,the effects of different C/N ratio and rotational speed(anaerobicaerobic alternating frequency)on wastewater treatment efficiency of low rotational speed sequential batch-drum rotating biological contactor(SB-DRBC)were investigated,and the optimal operating parameters were obtained by response surface analysis.The main conclusions are as follows:1)The TN removal rate of SB-DRBC increased by 31.3%(64.1% VS 32.8%)under sequential batch feeding compared with continuous feeding mode,and the biofilm contained higher abundance of GAOs(3.45%)and denitrifying bacteria(DNB).By analyzing the variation of dissolved oxygen in water and the filler,the results showed that a large anoxic zone was formed in the filler under the sequencing batch feeding mode,thus improving the denitrification efficiency of the system.Meanwhile,a denitrifying metabolic process based on intracellular organic carbon source(PHAs)as electron donor was found in the system.2)Under the condition of low rotation speed(0.5 rph),the biofilm can successfully enrich the high abundance of GAOs(20.42%)in the periodic anaerobic(underwater)-aerobic(in the air)condition,which can effectively convert the organic carbon source in the sewage into intracellular PHAs.At the same time,the use of zeolite modified biological filler can realize the adsorption removal of ammonium in sewage.After 17 days of operation,the removal rate of COD was above 84.4%,the removal efficiency of ammonia and TN was 73.1%,and no nitrate was detected in the effluent water.With the increase of rotation speed from 0.5 rph to 2 rph,the COD removal rate increases to94.4%,TN removal rate increases to 88.5%.The relative abundance of Candidatus Competibacter(GAOs)and DNB(Thauera and Comamonas)in biofilms decreased with the increase of rotational speed.3)The treatment of simulated high concentration wastewater with low rotational speed SB-DRBC was studied.Under the condition of HRT=6 h and rotation speed of0.5 rph,the removal rates of COD and TN reach 90.7% and 82.3% respectively for influent with 2 times concentration(COD=1016±25 mg/L,ammonia=82±3 mg/L).When the influent concentration is 4 times,the removal rates of COD and TN reach93.1% and 64.9%,respectively.When the influent concentration is 10 times and HRT is extended to 12 h,the COD and TN removal rates reach 85.7% and 39.1%.Therefore,biofilms can maintain high abundance of GAOs and DNB at 2 and 4 times concentration,while GAOs abundance in biofilms decreases significantly at 10 times concentration,and filamentous bacteria(Neomegalonema)become the dominant species.Combined with response surface analysis method,the optimal parameters of low speed SB-DRBC running 10-fold wastewater are speed =1.6 rph and HRT=30 h.Under this parameter,the COD removal rate is 87.1%,TN removal rate is 76.4%.