Research On The Combined Process Of DNBF-O₃-GAC For The Advanced Removal Of Nitrogen And Phosphorus And Metabolite

The secondary effluent from municipal wastewater treatment plant still contain relatively high concentration of nitrogen,phosphorus and difficult-biodegrade micro-pollutants,which can easily cause a serious impact to the water environment ecosystem when the secondary effluent used for landscape water supplying and groundwater recharging.Therefore,from the perspective of reuse water ecological security,studying new technologies which can simultaneously remove nitrogen,phosphorus and micro-pollutants efficiently has become an important content of the development and improvement of the reclaimed water treatment process.This research focuses on strengthening the efficiencies of advanced removal of nitrogen,phosphorus and micro-pollutants in the tail water from municipal wastewater treatment plant.In view of the characteristic of low C/N ratio in the reclaimed water,the denitrification biofilter with a new slow-release carbon source（SOC-F）/sponge iron/activated carbon media is tested,the combined process of DNBF-O₃-GAC is carried out for wastewater treatment plant secondary effluent with low C/N ratio,this process does not need addition carbon sources.Firstly,studies were conducted to examine the technical characteristics of nitrogen,phosphorus and micro-pollutants removal of the combined process by using synthetic effluent made from running water and chemicals.And then,correspondingly comparative studies were conducted by using the secondary effluent from municipal wastewater treatment plant,reasons of the disparities in the results were analyzed.At last,the microbial population structure and the strengthened removing mechanisms of nitrogen and phosphorus were discussed in a micro-level by adopting the Miseq high-throughput sequencing technologies and building the 16S rRNA bacterial gene clone library.The specific research results are as follows:The optimal HRT of the denitrification biofilter to remove nitrogen and phosphorus was 4h,average removal rate of TN and TP reached 85.7%and 93.37%,respectively,and the average COD in effluent was 29.2mg/L.What was more,89.65%of the TP was removed in the form of iron-phosphate precipitation.The result of XRD showed that the main composition of the sediment in the composite media phosphorus removal system is Fe₃（PO₄）₂.8H₂O.During the continuous operation of process,the composite media denitrification biofilter by mesh packing and spherical filling did not appear obvious packing layer congestion and there were no nitrate nitrogen,ammonia nitrogen accumulation.A high removal efficiency was achieved when the denitrification biofilter was applied to the actual tail water.Average removal rate of NO₃^--N in simulated and actual water period reached 93.12%and 80.16%,respectively,and the average removal rate of TN reached 78.65%and 76.99%.The denitrification system demonstrated the ability of stabilizing pH,which could maintain the pH value of the system in the weak alkaline range.Each processing unit has different functions:the changes of NO₃^--N,TN,TP and TFe mainly occurred in the denitrification biofilter;the removal of UV₂₅₄,turbidity and chroma mainly occurred in the ozone-activated carbon reactor.Three-dimensional fluorescence intensity of the effluent from the denitrification biofilter were obviously decreased by using 6mg/L ozonation.The bacteria related denitrification of the biofilm samples（A1）in simulated water period accounted for 38.06%of known microorganisms,sulfur autotrophic denitrifying bacteria and heterotrophic denitrifying bacteria accounted for 7.44%and25.95%respectively,the heterotrophic denitrification mainly;The bacteria related denitrification of the biofilm samples（A2）in actual water period accounted for 44.93%of known microorganisms,sulfur autotrophic denitrifying bacteria and heterotrophic denitrifying bacteria accounted for 31.53%and 13.4%respectively,the sulfur autotrophic denitrification mainly.As the carbon source consumption,the heterotrophic denitrification decreased gradually,sulfur autotrophic denitrification increased,which had made up for the decline of nitrogen removal efficiency caused by insufficient carbon source.The complementary effect of sulfur autotrophic denitrification and heterotrophic denitrification had extended the use period of the new slow-release carbon source.Phosphorus removal bacteria in the denitrification system included Thermomonas and Rhodocyclaceae_unclassified,in simulated and actual water period accounted for 6.3%and 6.92%respectively,the results showed that there was biological phosphorus removal in the denitrification system,and the proportion accounted for 10.35%.In this study,the combined process of DNBF-O₃-GAC is used to solve the problem of the lack of carbon source and the difficulty of removing nitrogen,phosphorus and metabolites simultaneously.The results are of great significance for improving the current status of high levels of nitrogen and phosphorus in the wastewater from the reclaimed water plant,enhancing the quality of the reclaimed water and promoting the process of turning wastewater into resource.It also provides technical reference and theoretical basis for practical engineering application.