| The high ammonia nitrogen and low C/N wastewater is a recognized refractory organic wastewater in the world.Biological treatment is the most widely used due to its cost-effectiveness.However,carbon shortages and low temperatures led to incomplete denitrification in low areas.To improve the ability of microorganisms to treat high ammonia nitrogen and low C/N wastewater,the research studied the enhancement effect of electrocoagulation technology on biological nitrogen removal.In this thesis,the nitrogen removal ability of bio-electrocoagulation systems with Fe-C electrodes was systematically studied in lab-scale systems and pilot-scale systems from the mechanism to the application under low-temperature conditions.Study on the enhancement of biological nitrification process by electrocoagulation technology in lab-scale systems is as follows.In this study,four cylindrical sequencing bath reactors(SBRs)were established.Two periodic reversal bio-electrocoagulation reactors composed of a pair of Fe-C electrodes and C-C electrodes,respectively,whereas the other two were an iron ion bio-reactor and a conventional bio-reactor,respectively.The experiment analyzed the pollutant removal,sludge characteristics,sludge particle sizes,nitrification rates,nitrification enzyme activities and microbial community structures,and systematically studied the effect of iron ions and electric field on the nitrification process in a PRBES with Fe-C electrodes.The experimental results showed that electrocoagulation was able to enhance the nitrification performance of activated sludge.Compared to the conventional bio-reactor,the NH4+-N removal rate was increased greatly in the PRBES with Fe-C electrodes,when temperature was 10?.Mechanism research illustrated that most of the NH4+-N were oxidized by microorganisms using O2 as a receptor in the PRBES,and the electrodes stimulated microbes to indirectly enhanced NH4+-N removal.The effect of the PRBES with Fe-C electrodes on microbes was primarily split into iron ions and electric field.Electric field improved the proton transfer and enzyme activity;iron ions increased the biomass and the levels of Nitrosomonas and Nitrobacter,both of which were the main microbes of the nitrification process.By comparison,the effect of irons on overall nitrification was stronger than that of the electric field in the PRBES.Study on the enhancement of biological denitrification process by electrocoagulation technology in lab-scale systems is as follows.Similar to the nitrification mechanism research,four bio-reactors were established.The experiment analyzed the pollutant removal,sludge characteristics,N2O and N2 production,denitrification rates,denitrification enzyme activities and microbial community structures,and systematically studied the influence of iron ions and electric field on the denitrification process in a PRBES with Fe-C electrodes.The experimental results showed that electrocoagulation was able to enhance the denitrification performance of activated sludge.Compared to the conventional bio-reactor,the COD and NO3--N removal rates were increased by 14.43%and 18.26%,respectively,in the PRBES with Fe-C electrodes,when temperature was 10?.Mechanism research illustrated that most of the nitrate were reduced by microbes in the PRBES,indicating that microorganisms played a crucial role in denitrification.The Fe-C electrodes stimulated the microorganisms to indirectly increase nitrate removal.In the PRBES,electric field provided electrons,and increased nitrogen transfer rate and the levels of Paracoccus;iron ions primarily increased the MLUSS and the denitrifying bacteria biomass.By comparison,the enhancement of iron ions on overall denitrification was stronger than that of the electric field in the PRBES with Fe-C electrodes.According to the mechanism studies,the electrocoagulation was able to enhance microbial nitrification and denitrification performance.Based on the mechanism research,the electrocoagulation was further applied to the actual high NH4+-N and low C/N ratio oil shale wastewater in the pilot-scale systems.However,oil shale wastewater is a poorly biodegradable refractory organic wastewater.Therefore,the activated sludge in the pilot-scale bioreactor was domesticated firstly.In this study,a multistage A/O membrane bioreactor was established.The dilution ratio of oil shale wastewater in the influent water was reduced gradually when C/N ratio was 8.After 72 days of acclimation,the NH4+-N and COD removal rates were 96.4%and 99.8%,respectively,when the influent NH4+-N concentration was increased from 100 mg/L to 1000 mg/L.The MLSS and MLVSS in the reactor were increased from 4239 mg/L and 3010 mg/L to 6116 mg/L and 5355 mg/L,respectively,and the activated sludge performance was good.The mixture reflux ratio test showed that when the mixture reflux ratio was increased from 100%to 400%,the TN removal rate was increased from 84.60%to 93.40%,whereas when the mixture reflux ratio was increased from 400%to 800%,the TN removal rate was only increased to 94.85%.After that,the COD and TN removal rates decreased to 90.89%and 81.27%,during the C/N ratio of the feed water decreased from 8 to 3.The two-stage inlet test showed that the TN removal rate increased from 81.27%to 88.23%in the case of a carbon to nitrogen ratio of 3.Study on the enhancement of nitrogen removal performance of activated sludge by an electric-coagulation multistage A/O membrane bioreactor(ECMMBR)treating oil shale wastewater at low temperatures is as follows.In this study,one conventional multistage A/O membrane bioreactor(MMBR)and one ECMMBR were established.The acclimated activated sludges were equally divided into two parts,which were placed in ECMMBR and MMBR,respectively.Based on the previous acclimation,the experiment reduced the C/N ratio again,optimized the test conditions and lowered the temperatures.The results showed that electrocoagulation was able to obviously promote the performance of MMBR,when the C/N ratio in the influent dropped from 3 to 2.Under the condition of 0.6-0.12 mg/L DO level,the nitrite nitrogen accumulation rates in the two bio-reactors were the best.In ECMMBR,the sludge particle size was increased due to electrocoagulation,and a micro-oxygen environment was generated,so that the ECMMBR can still maintain a high nitrite accumulation rate in the case of relatively high DO levels.When temperature was 10?,the electrocoagulation device was able to improve sludge performance and nitrification and denitrification rates,and enhance dehydrogenase and microbial population diversity.In addition,ECMMBR improved the relative abundance of Carnobacteriaceae_genus,Luteimonas and Trueperaceae,which were cold-resistant and hydrocarbon-bearing microorganisms.This may explain why the electric-coagulation technology enhanced system performance at low temperatures.The electrocoagulation device with Fe-C electrodes couples the dual functions of electric field and iron ions.The stimulation of activated sludge by this technology is not just a superposition of electric field and iron ions strengthening function.In addition to flocculation and precipitation of pollutants,the iron ions dissolved from Fe electrode are able to promote microbial metabolism and increase the growth rate of activated sludge.At the same time,the electric field can in turn further promote the absorption of iron ions by activated sludge,which further enhances the nitrogen removal performance.It indicates that bio-electrocoagulation technology is a combination of three fundamental processes(electric field,metal ions and microorganisms).These three factors are interdependent and mutually reinforcing,and are mixed into a new hybrid wastewater treatment technology.This thesis provides the theoretical basis and data support for the popularization and application of the periodic reversal bio-electrocoagulation technology.The results presented herein have provided a new way for WWTPs in cold areas to upgrade nitrogen removal. |
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