| The partial denitrification/anammox(PD/A)process is a completely new denitrification process.It can effectively reduce the demand for organic matter and sludge production,as well as reduce the generation of greenhouse gases,and can become one of the mainstream wastewater treatment methods for sustainability.However,PD/A has the defect that anaerobic ammonium oxidation(anammox)will produce a certain amount of nitrogen(NO3~--N,accounting for about 11%of total nitrogen),and carbon source addition is difficult to accurately control and fluctuate the accumulation of nitrite in short-range denitrification(PD).In order to better apply PD/A to urban mainstream wastewater,this project studied the rapid start-up of PD and PD sludge granulation for the treatment of low C/N urban sewage,and analyzed the effect of zero-valent iron(ZVI)on the denitrification performance of PD/A coupling process,and analyzed the activity and microbial community structure of functional bacteria in depth,and obtained the strengthening mechanism of ZVI on PD/A coupling process.The main findings are as follows:(1)Using the activated sludge of the anaerobic tank of the No.4 Sewage Treatment Plant in Xi’an,the control p H was 9.0±0.1,and the optimal C/N was determined to be 2.5 by batch experiments,and the nitrate-to-nitrite transformation ratio(NTR)reached 76.1%in the 19th and 81.1%in the 41st d,respectively,realizing the rapid start of PD.(2)The initial sludge volume index(SVI)of PD inoculated sludge was 221.5 m L/g.the specific denitrification rate(rno3)was 1.22±0.05 g N/(g VSS·d),and the VSS/SS was46.6±0.13%,and the sedimentation performance of sludge was poor.With the increase of total nitrogen load(NLR),the secretion of microbial extracellular polymeric substances(EPS)is promoted,and the increase of EPS promotes sludge granulation.The sludge SVI was reduced to 59.6m L/g,rno3 increased to 1.48±0.03 g N/(g VSS·d),MLVSS was 0.32±0.01g/L,and VSS/SS increased to 72.7±0.31%,which greatly improved the sedimentation performance of sludge and enhanced microbial activity.(3)In the PD/A coupling process,the concentration of chemical oxygen demand(COD)of the PD reactor was between 212.5～231.5 mg/L,the concentration of NO3~--N was between91.81～95.65mg/L,the average NTR was 83.3%,the total nitrogen concentration of the influent was between 161.11～168.45mg/L,and total nitrate removal(TNRE)reached 0.547kg N/(m~3·d)respectively,83.2%,COD removal load and COD removal rate reached0.51kg·COD/(m~3·d),93.6%,demonstrating the successful start-up of the PD/A coupling process and the ability to treat wastewater with low C/N ratios.(4)In the ZVI stage,the relative abundance of denitrifying bacteria(DNB)phylum and genus levels increased,the diversity of microorganisms of anaerobic ammonium oxidation bacteria(An AOB)increased,the total nitrogen removal rate of PD/A coupling process increased to 92.5±0.3%at this stage,and the concentration of nitrate nitrogen effluent decreased to 5.67±0.01mg/L.The results showed that the addition of ZVI had a good regulatory effect on the nitrogen removal microflora,which could significantly improve the denitrification efficiency of PD/A coupled system.(5)In the case of COD limitation,ZVI is added to the PD reactor,and the electron donor sin the reactor are mainly COD and ZVI,and the electrons are transmitted to the electron acce-ptor through a series of electron transport chains.At the same time,under the catalysis of nitr-ate reductase(Nar),electrons are consumed in the process of nitrate reduction to NO2~--N,wh i-ch not only reduces the addition of ZVI,but also effectively uses COD in water,ions enter a nammox,under the synergistic effect of anaerobic iron ammonia oxidation(Feammox)and ni t-rate-dependent ferrous oxidation(NDFO),the effluent NH4~+-N and NOx~--N are reduced,ther eby improving the effluent quality of low C/N sewage. |
PDF Full Text Request