Study On The Performance Of SBR-DNBF Process For Domestic Sewage Treatment

At present,C/N in urban domestic sewage is generally low,the secondary biological treatment technologies（A²/O、SBR、oxidation ditch,etc.）widely used in sewage treatment plants are difficult to meet increasingly stringent emission standards for nitrogen and phosphorus.In this paper,combined with the characteristics of SBR process,the SBR-DNBF process for strengthening nitrogen and phosphorus removal from domestic sewage is proposed,which mainly studies the effectiveness、influencing factors and pollutant removal of organic matter、nitrogen and phosphorus in SBR and DNBF.Furthermore,the dephosphorization of SBR and the denitrification kinetics of DNBF were studied.The biological activities and bacterial structure changes of sludge before and after acclimation in SBR reactor and the changes of biomass and biological activity along the DNBF were investigated.In addition,the operating characteristics of SBR-DNBF combination process were studied.The main research results are as follows:（1）The polyphosphate bacteria were enriched by A/O-SBR.After 7 days of continuous operation,the effluent TP concentration was lower than 0.5 mg/L,and the removal rate was over 90%.The polyphosphate bacteria were effectively enriched.The removal characteristics of pollutants showed that COD was mainly removed in the anaerobic section,and the COD removal rate slowed down with time.The concentration of NO₃^--N decreased continuously in the anaerobic section,and NO₂^--N was formed in the process,but it was finally removed by denitrifying bacteria in the anaerobic section,and the concentration of NH₄⁺-N in the aerobic section decreased rapidly,after 3 hours,the concentration was close to 0.With the progress of aerobic nitrification,the concentration of NO₃^--N increased continuously,and nearly 58.4%of TN was removed during the whole process.In the anaerobic section,the phosphorus-accumulating bacteria were subjected to phosphorus release,and the TP concentration in the reactor at the end of phosphorus release was 25.68 mg/L.Phosphorus was mainly removed in the aerobic section and gradually reached the equilibrium after aerobic 2.5 h,the final effluent TP concentration was 0.15 mg/L;（2）When the A/O-SBR process treats simulated domestic sewage,the effect of C/P on SBR pollutant removal efficiency indicates that when C/P is lower than 42,the effluent TP concentration cannot meet the requirement of less than 0.5 mg/L.The effect of COD and NH₄⁺-N removal is not significant with changing C/P.When C/P is between 36 and 48,the COD effluent concentration is lower than 42 mg/L,the removal rate is higher than 80%,and the NH₄⁺-N removal rate is close to 100%,the effluent contains almost no NH₄⁺-N;（3）The DNBF was quickly started by inoculation,and the NO₃^--N concentration of the effluent dropped to about 0.20 mg/L on the next day,and the removal rate was as high as 98.84%.The removal characteristics of pollutants along the path showed that the removal of NO₃^--N was mainly at 0-14 cm,the removal of NO₃^--N was as high as 94.8%,and the accumulation of NO₂^--N at 14 cm was the largest.The removal rule of TN is similar to that of NO₃^--N.The removal effect is best under 14 cm,accounting for 75.7%of the total removal rate.As the height increases,the TN removal rate slows down.The removal of organic matter was mainly concentrated in the DNBF below 14 cm,accounting for 92.3%of the total removal rate.As the height increased,the COD concentration decreased.The TP concentration does not change significantly with the height of the filter layer,and fluctuates around 0.5 mg/L;（4）When the DNBF was used to treat the secondary effluent in the simulated city.,the effects of different C/N and HRT on the treatment efficiency were investigated.The results showed that TN and COD could be removed well under the condition of C/N of 4 and HRT of 4 h.The effluent TN and COD concentrations are less than 10 mg/L and 50 mg/L.The effect of DNBF on phosphorus removal is not obvious,and the changing C/N and HRT have little effect on the TP concentration change;（5）In the SBR reactor,when the temperature is 20℃,the influent TP is 5 mg/L,and the C/P is 48.The kinetic model of phosphorus release is C=53.33998×(1-e^-0.29187t),the maximum phosphorus release concentration is 53.34mg/L,the rate constant of phosphorus release is 0.29187.The kinetic model of phosphorus uptake is C=25.7552×e^-0.78136t,the maximum phosphorus uptake is25.7552 mg/L,and the rate constant of phosphorus uptake is 0.78136;In the DNBF reactor,when C/N is 5,the temperature is 25℃and the filtration rate is 0.069 m/h,that is,HRT is 4 h,the denitrification kinetic equation of the DNBF at this time is C=C_0·e^-0.2072h.When the rate range is 0.086-0.138 m/h,that is,the HRT range is 2-3.2h,the denitrification kinetic equation at this time is C=C_0·e^{（-0.04774+0.00176/v）·h};（6）After the domestication of the sludge in the SBR reactor,the rate of phosphorus release and the rate of phosphorus uptake are greatly improved,the effect of removing phosphorus is obviously enhanced,and the microbial activity is also greatly increased,which has good removal performance for pollutants.At the same time,through the analysis of the microbial flora structure,Proteobacteria and Bacteroidetes are the dominant bacteria on the“gate”level of the mud and domesticated sludge,which are the key to remove phosphorus and organic matter,respectively.52.09%rose to 79.33%,and the ability to remove pollutants increased.Chloroflexi,which causes sludge bulking,has a lower proportion after acclimation,and sludge settling performance is improved.Nitrospirae,which is closely related to nitrifying bacteria,does not change much before and after domestication.Planctomycetes and Firmicutes can not play the role of their functional bacteria,are inhibited in the operating environment of SBR,and the proportion has decreased after acclimation;Atthe"genus"level,thepolyphosphatebacteria Candidatus_Accumulibacterandthepolysaccharidestrain Candidatus_Competibacterwereenrichedandaccumulativelyenriched.Nitrosomonas and Nitrospira,which determine the nitrification effect,were effectively increased after acclimation,similar to autotrophic denitrifying bacteria.Comamonadaceae and Hyphomicrobium are inhibited;the proportion of Zoogloea,which is a genus of micelles,is increased,and the sedimentation performance of sludge is effectively improved;In the DNBF reactor,through the analysis of biomass and biological activity under different packing layer heights,the biomass and biological activity decreased with the increase of the height of the packing layer.The biomass and biological activity at the bottom were 1.58 times and 2.63 times of the top,respectively.