Study On Optimization Of An Electrode Dependent Ammonium Oxidation System And Effect Of Nano-Microplastic On Its Operational Performance

The discovery of electrode ammonia oxidation has provided a new idea for the development of new technologies for biological denitrification,which can compensate for the shortcomings of other biological denitrification technologies in the treatment of wastewater containing ammonia and nitrogen.However,in bioelectrochemical systems（BES）,the cultivation time of electroactive ammonia oxidation biofilms is long,the intensity of electrode ammonia oxidation is usually low and the performance of the system in terms of nitrogen removal and electricity production is not satisfactory.In view of this,measures need to be taken to optimise the electrode ammonia oxidation system.On the other hand,as more and more microplastics are discharged into the water environment,the impact of microplastics（especially nano-microplastics）on wastewater treatment processes is of increasing concern,however,the effect of nano-microplastics on the operational performance and stability of electrode ammonia oxidation processes is still less reported.In this study,a two-chamber BES was used as the experimental device to investigate the occurrence and enhancement mechanism of electrode ammonia oxidation in the system by setting three-dimensional electrodes in its anode chamber.The effect of typical types of nano-microplastics on the operational performance and microbiological properties of the electrode ammonia oxidation BES was then investigated,and the corresponding mechanisms of action were first explored.The results of the study can provide theoretical basis and data support for the optimization and stabilization of the electrode ammonia oxidation process.The main research contents and results were as follows:（1）A three-dimensional electrode was installed in the anode chamber of the electrode ammonia oxidation BES to investigate the performance of the system and its microbiological characteristics when different types of fillers were used as the three-dimensional electrode.The results show that the physicochemical characteristics of the filler in the three-dimensional electrode can significantly affect the microbial community structure in the electroactive ammonia oxidation biofilm when treating ammonia-nitrogen wastewater with the electrode ammonia oxidation BES,which in turn can result in differences in the performance of the device in terms of nitrogen removal and electricity production.When pyrite was selected as a filler in the three-dimensional electrode electrode compared to quartz sand and zeolite,its larger specific surface area,higher EC value and Fe content increased the abundance and activity of functional microorganisms（especially Nitrosomonas,Geobacter,Empodebacter and Candidutus Brocadia）involved in the ammonia oxidation reaction at the electrode.The system achieved TN and NH₄⁺-N removal rates of（83.45±6.00）%and（92.86±5.16）%,respectively,with a peak output power density of 0.60 W/m³.（2）The effect of different concentrations of PVC in the feed water on the denitrification performance of the system and its microbial community structure was investigated using an electrode ammonia-oxidizing BES set up with three-dimensional electrodes as an experimental setup,and polyvinyl chloride（PVC）as a typical type of non-biodegradable nanomicroplastic.The results showed that the concentration of PVC in the feed water affected the number and activity of the nitrogen removal microorganisms in the electrode ammonia oxidation system,which in turn affected its nitrogen conversion rate,when the concentration of PVC in the feed water was increased from 0 to 20 mg/L,the community structure in the electroactive ammonia oxidation biofilm was not significantly affected,but the nitrogen removal performance of the BES increased slightly due to the adsorption of PVC on nitrogen,and the TN and NH₄⁺-N removal rates were（69.41±5.84）%and（80.44±5.66）%,respectively.When the influent PVC concentration was>20 mg/L,the abundance of the dominant bacterial genera（Nitrosomonas,Candidatus Brocadia,Geobacter and Empodebacter）involved in the electrode ammonia oxidation reaction in the BES decreased continuously,which in turn inhibited the electrode ammonia oxidation in the system and led to the deterioration of the system denitrification performance.At a PVC concentration of 100 mg/L in the feed water,the TN and NH₄⁺-N removal rates of the BES decreased to（25.62±1.34）%and（31.61±1.31）%,respectively,and the peak output power density was only 0.29 W/m3,thus indicating that excessive concentrations of PVC in the feed water inhibited the performance of the electrode ammonia oxidation system.（3）The effects of different concentrations of PBS in the feed water on the denitrification performance of the system and its microbial community structure were investigated using an electrode ammonia oxidation BES with three-dimensional electrodes and polybutylene succinate（PBS）as a typical type of biodegradable nanomicroplastic.The results showed that the concentration of PBS in the feed water affected the number and activity of the denitrifying microorganisms in the electrode ammonia oxidation system,which in turn affected its nitrogen conversion rate.When the concentration of PBS in the feed water increased from 25 to 100 mg/L,the abundance of denitrifying bacteria in the BES increased,and the bacteria participated in the electrode ammonia oxidation process,which enhanced the denitrification effect of the system.At this time Nitrosomonas and Candidatus Brocadia were still the two main functional microorganisms in the system,while Dechloromonas and Thauera dominated the denitrification process,and the increased abundance of Geobacter and Empodebacter also contributed to the electrode ammonia oxidation in the system.At a PBS concentration of 100 mg/L in the feed water,the electrode ammonia-oxidising BES provided ideal denitrification performance with TN and NH₄⁺-N removal rates of（88.20±2.42）%and（92.95±2.36）%,respectively.A certain concentration of PBS in the feed water can be used as a solid slow-release carbon source to optimise the operational performance of the electrode ammonia-oxidising BES compared to the difficult-to-biodegrade nanomicroplastics.