| In recent years,water eutrophication frequently occurs,which leads to the deterioration of water quality in a large number of waters and seriously affects the health and ecological environment of residents.It has been paid much attention by researchers in the field of water environment.The high content of nutrients such as nitrogen and phosphorus in the water is the key reason for the eutrophication of the water body.Therefore,the efficient removal of nitrogen and phosphorus sources in sewage has become an important task in the field of sewage treatment.Aerobic granular sludge(AGS)is a kind of granular activated sludge,which has received great attention in the field of wastewater treatment due to its advantages of good sedimentation performance,high microorganism concentration and simultaneous nitrogen and phosphorus removal.The AGS process usually adopts a single influent-aeration operation strategy to start by A/O mode,but it is difficult to perform denitrification under aerobic conditions in the initial stage of operation.It will be a large amount of nitrate nitrogen in the system,inhibiting anaerobic phosphorus release of phosphorus accumulating organisms(PAO).However,phosphorus release is a prerequisite for ensuring good phosphorus removal performance of PAO,and studies have shown that PAO will form positively charged particles and calcium phosphate precipitates during the phosphorus removal process,which can promote sludge aggregation and play an important role in achie ving rapid granulation.In addition,the anaerobic time in the operating cycle also has an impact on the phosphorus release of PAO.And the consumption of carbon by microorganisms in the anaerobic environment leads to the lack of matrix in the aerobic environment,which can inhibit the excessive proliferation of heterotrophic bacteria and help maintain the stability of particle structure.Moreover,domestic sewage has a low C/N.In the traditional denitrification process,the nitrogen is converted twice dur ing the denitrification process,which causes a waste of carbon source and cannot efficiently use the carbon source.This limits the denitrification process and causes the effluent TN concentration to exceed the specification.The short-range denitrification process has the advantages of reducing energy consumption and saving 40% of the carbon source.It is suitable for low C/N wastewater,so it is important to enrich ammonium-oxidizing bacteria(AOB)and inhibits nitrite-oxidizing bacteria(NOB)activity,controlling the nitrification process in the nitrosation stage is very important for the realization of the entire process.Therefore,this paper proposes the intermittent influent-intermittent aeration operation mode.It adopts adopts the multiple influent-aeration strategy in the cycle to conduct the nitrification and denitrification process for multiple times,by reducing the concentration of nitrate nitrogen and its inhibition of PAO,the phosphorus removal effect is improved and the formation of granular sludge is promoted.First,compared the single influent-aeration operation strategy,the impact of multiple influent-aeration operation strategy on the AGS system was explored.Then under the multiple influent-aeration operation strategy,the effects of different anaerobic time on AGS system with the intermittent influent-intermittent aeration were explored.At the last of the experiment,intermittent aeration was used to suppress NOB activity,and achieve the conversion of the full-range nitrogen and phosphorus removal process to the short-range nitrogen and phosphorus removal process on AGS system with intermittent influent-intermittent aeration.The effects of different ratio of aeration time to anoxic time on intermittent influent-intermittent aeration AGS short-range nitrogen and phosphorus removal processes were investigated.In the study of AGS full denitrification and dephosphorization process with intermittent influent-intermittent aeration operation mode,this test inoculate d the sewage treatment plant return sludge in sequencing batch reactor(SBR),respectively adopt single/multiple influent-aeration operation strategy,and studied the change of pollutant removal performance and particle characteristics of AGS system.The results of the experiment found that the two reactors,which were operated with a single influent-aeration operation strategy and multiple influent-aeration operation strategy,respectively,took 56 days and 39 days to achieve sludge granulation.During the granulation process,the nitrate concentration and TP concentration of the effluent in the latter reactor were generally lower than the former.At the end of the operation,the average particle size of the granular sludge in the two reactors was 740 μm and 791 μm,respectively.The particle size of the granular sludge in the reactor operated by the multiple influent-aeration operation strategy was larger,and the particle shape was more rounded.In order to further explore the impact on denitrifying phosphorus accumulating bacteria(DPAO),during the test,batches of granular sludge were tested every 20 days.The ratio of DPAO in all PAO,δ,in the two reactors increased from the initial 11.17% to 25.47% and 34.08%,respective ly,and the DPAO was enriched.At the end of operation,the average COD,TP and TN concentration of effluent in the two reactors was 24.8 mg/L,11.2 mg/L,0.40 mg/L,20.9 mg/L,8.9 mg/L and 0.37 mg/L,respectively.It had a good treatment effect on COD,TP and TN.In order to clarify the effect of anaerobic time on the intermittent influent-intermittent aeration AGS system,this test inoculated the sewage treatment plant return sludge in SBR.It used intermittent influent-intermittent aeration operation mode at different anaerobic time(30 min,60 min,90 min and 120 min)to study the pollutant removal performance and particle characteristics of domestic sewage AGS system.Four groups of reactors operating under different anaerobic times successfully achieved sludge granulation after 56 d,48 d,39 d and 35 d,respectively.After the formation of AGS,the phosphorus removal performance gradually deteriorated in the reactors with anaerobic time of 30 min and 60 min at 43 d and 47 d.The analysis of the change in pollutant concentration during the cycle showed that the nitrate nitrogen released phosphorus to the phosphate accumulating organisms had inhibition.After prolonging the anaerobic time from 30 min and 60 min to 90 min,the phosphorus removal performance gradually recovered.When running to 63 d,the particles disintegrated in the reactor with an anaerobic time of 120 min,and the performance of pollutants was affected.The average removal rates of COD,TP and TN decreased to 78.0%,83.4%,68.8%,and after operation the system was restored.In order to further explore the effect of anaerobic time on DPAO,batch experiments were conducted on the cultured granular sludge every 20 days during the test period.It was found that the δ values in the four reactors increased from the initial 11.17% to 14.62%,16.11%,20.39% and 22.91%,respectively.DPAO was enriched to varying degrees.In the later stage of the experiment,in order to study the short-cut nitrogen and phosphorus removal process of AGS based on intermittent influent-intermittent aeration,three SBR reactors were inoculated with mature AGS,with different ratio of aeration time to anoxic time(2 min: 6 min,4 min: 4 min,6 min: 2 min),respectively.The ratio of aeration time to anoxic time was 6 min: 2 min,the particle characteristics are stable and the PN/PS value was stable,with an average of 1.39.The ratios of aeration time to anoxic time were 2 min: 6 min and 4 min: 4 min,the particle stability was affected in the early stage of operation,and the settlement performance was reduced.PN/PS increased to 1.82 and 1.69,and then gradually decreased to 1.38 and 1.39.The sludge volume index(SVI)increased to 38.4 m L / g and 39.4 m L / g,respectively,but the particle performance gradually recovered after running.And the ratio of aeration time to anoxic time was smaller,the DO concentration in the cycle was lower,the inhibitory effect on NOB was better,and the short-range nitrogen and phosphorus removal effect was better,and the effluent COD,TP and TN met the IA standard of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants(GB18918-2002).In order to further explore the impact of ratio of aeration time to anoxic time on the DPAO enrichment,batch experiments were conducted on the cultured granular sludge every 20 days during the experiment,and it was found that the δ values in the three reactors increased from 25.74% to 46.56%,44.91% and 41.39%,and the DPAO content had increased. |
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