Application Of Slow-release Carbon Source In Denitrification Filter And Study On Denitrification Performanc

As the standard of effluent quality of sewage treatment plant is becoming more and more stringent,it is urgent to raise the standard of sewage treatment plant.Generally,due to the low content of C/N in the secondary effluent of sewage treatment plants as well as the limited effect of biological denitrification process in China,the supplement carbon source is still needed in application of biological denitrification process.However,it is inadequate to use traditional carbon sources such as methanol and ethanol,which could result in excessive or insufficient dosage and low utilization rate of carbon sources and,as a consequence,leading to unstable effluent quality.Therefore,the search for a new type of slow-release and efficient solid carbon source as denitrification filter packing and biofilm carrier has become a new hot spot in denitrification research.In this study,high molecular polymer was selected as the slow-release carbon source,and the denitrification biological filter process based on slow-release carbon source and granular activated carbon was used to carry out the experimental study on denitrification of tail water of sewage treatment plant,and the operation effect of the process was investigated to provide technical reference for deep denitrification of sewage.The feasibility of polymer as slow release carbon source material was investigated by static carbon release experiment and denitrification filter biofilm start-up experiment.The denitrification performance of denitrification filter filled with slow release carbon source and granular activated carbon was investigated by continuous flow denitrification experiment.By changing the operation parameters of denitrification filter,the operation effect of reactor under different operating load was investigated.The spatial distribution of microorganisms in different reactors was studied by high-throughput sequencing.The specific conclusions are as follows:（1）The static carbon release experiments of PBS,PCL,PLA and PBAT were carried out.The results show that the static carbon release rate of PCL,PBS and PBAT is faster,of which PBS material has the highest carbon release rate,while PLA material has the lowest carbon release rate.The average carbon release rate is as follows:PBS（2.48 mg/（g·d））>PCL（2.26mg/（g·d））>PBAT（1.44 mg/（g·d））>PLA（0.45 mg/（g·d））.（2）The biofilm start-up experiment was carried out by using PBS,PCL and PBAT as slow release carbon source and denitrification filter filler.Under the condition of NO₃^--N concentration of 20 mg/L and HRT=2 h,the biofilm formation time of PBS and PCL reactor was only 6 days,while the time of PBAT reactor was about 20 days,.After stabilization,the NO₃^--N removal rate of PBS and PCL reactor was more than 99%,while the rate of PBAT reactor was about 73%.There was no NO₂^--N accumulation in PCL reactor and PBS reactor during the start-up of biofilm,and the NO₂^--N was kept below 0.5mg/L.（3）In the operation experiment of denitrification filter,the denitrification volumetric load of PCL reactor and PBS reactor reached the maximum when the influent NO₃^--N concentration was 50mg and the temperature was 30±2℃.After stable operation,the average effluent NO₃^--N concentration of PCL reactor and PBS reactor were 12.74 mg/L and 7.95 mg/L,respectively,and the average NO₃^--N removal rates were 74.69%and 84.22%,respectively.The average volume load of denitrification was 0.842 kg/（m3·d）and 0.935 kg/（m3·d）,respectively,and the treatment effect of PBS reactor was better.（4）The results of high-throughput sequencing showed that the microorganisms at the gate level of PCL reactor and PBS reactor were mainly Proteobacteria,Chloroflexi and Bacteroidota.In terms of spatial distribution,the abundance of Proteobacteria in both reactors decreased with the increase of filter depth.At the genus level,Comamonadaceae-unculture,Comamonas,Anaerolineaceae＿uncultured and NS9 marine group＿norank are the main genera in the two reactors.Comamonadaceae＿uncultured and Comamonas inβ-Proteus are the main denitrifying bacteria.The spatial distribution of the two genera in the two reactors is similar to that of Proteus,and both decrease with the increase of filter depth.