Study On Treatment Of Nitrogen-containing Wastewater By Dissimilar Iron Reduction Coupled With Anaerobic Ammonium Oxidation

The pollutants in the nitrogen-containing wastewater which was discharged from industrial production and daily life will not only break the ecological balance of water environment,but also endanger human health.Traditionally,nitrogen removal from nitrogen-containing wastewater could be achieved conventionally by biological denitrification processes such as nitrification-denitrification and anaerobic ammonia oxidation（Anammox）,however,the traditional nitrification-denitrification requires aeration and external carbon source during operation,meanwhile,the functional microorganisms of Anammox proliferate slowly and are sensitive to environmental conditions,which makes them restricted in industrial application.Dissimilar iron reduction coupled with anaerobic ammonia oxidation（Feammox）is a metabolic mechanism which exists widely in natural environment and plays an important role in the nitrogen cycle,it has a wide range of functional microorganisms,strong adaptability and no need for aeration and dosing of exogenous substances during operation.It is a denitrification approach with great potential and advantages,which is greatly different from traditional nitrification-denitrification and Anammox.In this study,the diluted biogas liquid of waste activated sludge was selected as the treatment object,and ferrihydrite was added to the anaerobic reactor to drive Feammox to occur in it.At the same time,¹⁵N labeled isotopic was used to confirmed the existence of Feammox.This study investigated the effect of anaerobic denitrification through Feammox in the reactor after driving it,and explored the influence and mechanism of adding humus,and provided practice and theory for the application of Feammox.The main results are as follows:（1）The medium was as follows:Mg Cl₂·6H₂O（0.4 g/L）,Ca Cl₂·H₂O（0.1 g/L）,¹⁵NH₄Cl（0.1 g/L）and KH₂PO₄（0.6 g/L）,1 m L/L vitamin solution,1 m L/L trace element solution,30mmol/L bicarbonate buffer and 2 mmol/L acetate,mixed it with inoculated sludge to culture anaerobically,and set up the control group（without ferrihydrite）and the experimental group（add ferrihydrite）,after 30 days of anaerobic incubation,a large amount of ³⁰N₂was detected in the headspace of the experimental reactor using a gas chromatography equipmented with mass spectrometry,which was confirmed that the Feammox was successfully driven in the anaerobic reactor after adding Fe（III）.The diluted biogas liquid of waste activated sludge with concentration of about 100 mg/L NH₄⁺-N was used as the treatment object,set up the control group（without ferrihydrite）and the ferrihydrite group（add ferrihydrite）,after 48 days of anaerobic incubation,the NH₄⁺-N removal efficiency of the ferrihydrite group was 72.4%,which was 64.8%higher than the control group,and the total nitrogen removal efficiency increased by more than 50%.At the same time,the intermediate products NO₂^-and NO₃^-were detected in the reactor.A large amount of Fe（II）was produced in the ferrihydrite group,and the production of Fe（II）was synchronized in time with the decrease of NH₄⁺-N concentration.The results of microbial community analysis and real-time quantitative PCR analysis（q PCR）showed that the iron-reducing bacteria such as Geobacter and Feammox functional microorganism Acidimicrobiaceae A6 bacteria were enriched in the ferrihydrite-added reactor.（2）The diluted biogas liquid of waste activated sludge with the NH₄⁺-N content about100 mg/L was used as the treatment object.After the ferrihydrite was added to the reactor,set up the Fe reactor（without humus）and the Fe-HA reactor（add humus）,after 48 days of anaerobic incubation,the removal efficiency of NH₄⁺-N in the Fe-HA reactor was 88.3%,increased by 15.9%,and the total nitrogen removal efficiency increased by 16.2%.The Fe（II）production rate in the Fe-HA reactor was 38.3 mg/L/d,and the iron reduction ratio was 89.4%,which were increased by 61.6%and 43.2 percentage points respectively.Different forms of iron oxides in the reactors were extracted to confirm the proportion of them,and scanning electron microscopy（SEM）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）as well as other characterization methods were used to analysis their morphology and crystal forms,the results showed that more stable and difficult-to-use iron oxides were produced in the Fe reactor.The microbial community analysis results showed that the microbial community in the Fe-HA reactor was more abundant,and the iron-reducing bacteria such as Geobacter、Desulfuromonas、Desulfovibrio、Desulfomicrobium were further enriched.