Effect Of Electromagnetic Wave Loading Returned Sludge On A/A/O Progress

With the rapid advancement of urbanization,the production of sludge has increased drastically,and reduction of excess sludge has become extremely urgent.At present,researchers have applied electromagnetic wave to dewatering of excess sludge to achieve sludge reduction（sludge volume reduction）.However,there were few reports on the reduction of sludge during wastewater treatment based on the solubilization and biological effects of electromagnetic waves.In this paper,2450MHz electromagnetic wave was applied to disposal of return sludge of A/A/O process,and revealed the optimal operating parameters of reducing sludge by changing the loading power,loading time,the percentage of return sludge loading.Moreover,we analyzed the influence mechanism of dissolution effect and biological effect of electromagnetic wave on thepollutants-removal abilityand the reducing amount of excess sludge of A/A/O through detecting the solubilization of various pollutants in the returned sludge and the variations of biological characteristicsbefore and after electromagnetic wave loading.In this paper,the uniform test illustrated that the optimal operation conditions of reducing excess sludge were:DO of aerobic tank was 4.50 mg/L,HRT was7.50 h and MLSS was 3.50 g/L,respectively.Then,the experiment of loading electromagnetic wave on returned sludge was carried out under these conditions.1.Result of single factor test of returned sludge by electromagnetic wave loading inA/A/O system.（1）When loading power changed from 0 to 420W,the COD,NH4⁺-N,TP,and SS of effluentgradually improved with the increase of the loading power,and the ranges of meeting the effluent standards were:0-370W,0-395W,0-308W,0-420W.TN of effluent could reduced to less than 15mg/L when loading power was 210-360W,when the loading power was above 360W,TN of effluent was over the standard.（2）When loading time changed from 0 to 75s,COD,NH4+-N,TP,and SS of effluent gradually improved with the increase of loading time,and the ranges of loading time of meeting the effluent standards were 0-60s,0-63s,0-47s,0-72s.The TN of effluent educed to less than 15mg/L when the loading time was 17-57s,while it began to exceed the standard after 57s.（3）When the percentage of returned sludge loading changed from 0%to 80%,COD,NH₄⁺-N,and SS concentrations of effluent began to exceed the standard when the percentage was less than 16%,18%,and 12%.And TN of effluent can meet the standard when percentage of returned sludge loading was 20%-40%,while it began to exceed the standard when the percentage was less than 16%.When the loading percentage was less than 40%,theTP of effluent,the lowest value of 0.95mg/L,reached A of level one standard when the loading percentage was 20%.However,the TP of effluent meet the standard again when the loading percentage was more than62%.（4）When the loading power was less than 420W and the loading time was less than 60s,the excess sludge gradually decreased with the increase of loading power and loading time,and it decreased from 12.87g/d of unloaded system to 7.89g/d and7.83g/d of loaded system with 420W and60s.However,when theloading time was extended from 60s to 75s,the excess sludge did not decrease but increased to 8.36g/d.When the percentage of returned sludge loading was reduced to 10%,the excess sludge suddenly dropped to a minimum value of 6.42 g/d,but when increased to 80%,the reduction rate of excess sludge was only 6.40%.According to the effluent quality and the amount of excess sludge of A/A/O with different electromagnetic wave loading condition,the best combination of parameters was selected:loading power at 265W,loading time at 45s,and percentage of returned sludge loading at 30%.Under these operations,the COD,NH₄⁺-N,TN,TP and SS concentrations of effluent were 42.46 mg/L,3.22m/L,12.69mg/L,1.06mg/L,4.1mg/L,repectively.The excess sludge amount was 9.23g/d,and the sludge reduction rate was28.30%.2.The effect on microbial communities when electromagnetic wave was loaded on returned sludge in A/A/O system.（1）Surely,some microorganisms in the returned sludge would die after dealing with electromagnetic wave.However,the numbers of live bacteria and biological activities of sludge in the system increased,and the abundance of microbial populations significantly increased after the loaded sludge returning to A/A/O system comparing with traditional A/A/O systems.The dominant bacteria like Zoogloea,Dechloromonas,Tolumonasandotherheterotrophsincreased,andthe Clostridium_–sensu_-strict appeard which was an anaerobic fermentation bacterium and could reduced the amount of sludge.（2）According to the results of comparative analysis about functional bacteria,the proportion of Nitrospira in the system was significantly reduced while new nitrifying bacteria Nitrolancea was appeared after the return sludge loading withelectromagnetic wave.Besides,various heterotrophic denitrifies accounted for a larger proportion,but the proportion of anaerobic ammonia-oxidizing bacteria was significantly reduced or even disappeared and the proportion of aerobic denitrifying bacteria was basically unchanged.The proportion of aerobic phosphorus-removing Acinetobacter decreased significantly,but the proportion of denitrifying phosphorus-removing bacteria was significantly increased.In the genus of sludge reduction-related bacteria,the predation genus Bdellovibrio disappeared and Lysobacter decreased significantly,but the richness and diversity of the slow-growing anaerobes increased.3.Influence mechanism of solubilization of electromagnetic wave in A/A/O system.（1）During the process of electromagnetic wave loading return sludge,the dissolution of SCOD resulted to the total amount of COD and C/N increased in the system.However,it has no significant effect on the COD of effluent.When loading power was 132-360W,the loading time was 17-57s,and the loading percentage was20%-40%,the TN of effluent was below 15mg/L.The solubilization of NH4⁺-N was low,and thus the effect on the NH₄⁺-N of effluent was little,while the TP of effluent was affected by the solubilization of phosphorus.Interestingly,during the loading process,the SS of the returned sludge supernatant and effluent both increased,without obvious deterioration phenomenon occurred.（2）The solubilization of organic matter significantly effected the sludge reduction during the process of dealing returned sludge with electromagnetic wave.When the loading power,loading time,and loading percentage were changed,the total amount of SCOD was significantly negatively correlated with the amount of excess sludge,with the linear correlation coefficients were:0.996,0.952,and 0.647,respectively.4.Influence mechanism of biological effects of electromagnetic waves on A/A/O system（1）Although the biological activity of return sludge reduced,but the biomass and dehydrogenase activity of sludge in system increased under the electromagnetic wave loading condition which was also conducive to the improvement of organic matter degradation and sludge reduction.（2）Electromagnetic wave,which was loaded on the returned sludge,had little effect on the endogenous respiration rate of the aerobic tank sludge,but it could improve the aerobic respiration rate.The SOUR of aerobic tank sludgeincreased to the peak valueof 55.14mgO₂/（gMLSS·h）when loading power was 210 W,51.79mgO2/（gMLSS·h）with loading time of 45 s,51.79 mgO2/（gMLSS·h）with loading percentage of 20%.（3）During the process of loadingelectromagnetic wave on return sludge,the proportions of Nitrosomonas,Dechloromonas,Azospira,Azonexus,Thauera,Arcobacter,Predator Lysobacter,and Bdellovibriowerereducedto some extent,but Nitrolancea,Arcobacter and Enterococcus,Clostridium–sensu-strict,Sulfurospirillum,Paludibacter,Fusibacter,Ignavibacterium,Methylotenera,Enterococcus,etc,could survive in large amounts due to their strong resistance to electromagnetic waves.