Study On The Denitrification Performance Of Solid Carbon Source Denitrification Biofilm Reactor

According to the Ministry of Housing and Urban statistics,China's urban sewage treatment rate has reached 91% by the end of 2015,but the eutrophication of water is still serious.Facing the pressure to improve the quality of the environment,the upgrading and reconstruction of the sewage plant is imminent and irresistible trend.In the process of upgrading and reconstruction,total phosphorus(TP)and total nitrogen(TN)have attracted much attention.In contrast,TP can be achieved by strengthening the chemical phosphorus removal and efficient precipitation separation,while TN can only be achieved through biological effect.Due there are many factors that affect the biological denitrification,TN has become the difficulty of upgrading and reconstruction,which is especially prominent in low-carbon source sewage treatment system.At present,the addition of methanol,glucose,acetic acid and other carbon sources have become the necessary measures of the low-carbon source sewage treatment plant.However,a large number of operational practices have shown that due to the effects of molecular diffusion dilution,the utilization of these additional carbon sources is low.In this case,the use of slow-release solid carbon source as a biological carrier of solid carbon source denitrification technology has become a new research focus.Based on the previous research of the research group,the solid carbon source of polycaprolactone(PCL)was blended and modified,and plate solid carbon source material was prepared.Based on this,vertical fold streaming denitrification reactor(VFSDR)was built,taking the tail water of biochemical pool as the research object,according to the purpose of upgrading and reconstruction,the effects of HRT,nitrate load and temperature on the denitrification efficiency of VFSDR were studied.And the microbial community composition and carbon consumption in the reactor were investigated.The main findings and conclusions are as follows:(1)The plate solid carbon source material was prepared by blending the thermoplastic starch,PCL,etc.The water-soluble properties of the modified carbon material were studied by clean water release test,it was found that the carbon-releasing ability of the modified solid carbon source material was higher than that of polycaprolactone,and the carbon sequestration rate was stable.The surface morphology of the modified solid carbon source material was observed by SEM,many grooves and holes were observed after being used by microorganisms,it proved the degradation and utilization of the material by microorganisms.The FTIR characterization of the material found that the starch in the modified solid carbon source material was well preserved,and PCL interacted with the thermoplastic starch during the blending process.(2)It was necessary to start VFSDR for 8 days.After the stable operation,TN concentration of the effluent were between 1.14 and 3.56 mg/L,and would not cause COD exceeded.The HRT was regulated by a peristaltic pump,it was found that with the decrease of HRT,the effluent COD decreased gradually,the denitrification rate decreased gradually,and the removal rate of TN decreased gradually.When the temperature was between 27? and 29?,the HRT required to remove 5 mg/L TN was 0.5h,and the HRT required to remove 10 mg/L TN was 1h;Varying the concentration of nitrate in water found when it from 20 mg/L to 40 mg/L,TN concentration of the effluent increased,the rate of denitrification increased.When the concentration of nitrate in water was 40 mg/L,the maximum denitrification rate was up to 13.63 mgN/(L·d),the denitrification rate and the concentration of nitrate in the influent were found in the significant linear correlation(R2=0.9822).The lower the temperature,the higher the concentration of nitrate nitrogen in the effluent,the worse the denitrification effect,the lower the COD concentration,the lower the denitrification rate,and when the HRT is 2h,the temperature corresponding to removing 5 mg/L TN is not less than 15?,the temperature corresponding to removing 10 mg/L TN is not less than 20?.To achieve stable emission of TN at lower temperatures and smaller HRT conditions,it can be obtained by increasing the density of the solid carbon source plate in the reactor.(3)In order to study the composition of the microbial community in the reactor,the nine sites were identified in the three chambers by high-throughput sequencing,found that the biofilm was rich in community structure,including Acidovorax,unclassified_f_Comamonadaceae and other degrading bacteria,Flavobacterium and other fermentation acid bacteria,as well as Hydrogenophaga,Denitratisoma,Bacillus and other denitrifying bacteria,to achieve solid carbon source materials from degradation to fermentation and then to denitrification denitrification process.(4)The carbon consumption of the modified solid carbon source material was 2017.12 mg/d(COD)in the 10 days of the test.The amount of carbon dissolved in the material was 1863.06 mg/d(COD),which accounted for 92.4% of theoretical carbon consumption,it showed that the dissolution of organic matter in modified solid carbon source material was mainly due to the action of microorganism.The theoretical carbon consumption of the denitrification process was 1.66 g modified material/g NO3-,and the total carbon consumption was 2.12 g modified material/g NO3-,the organic carbon consumption during the denitrification process was 78.3% of the total carbon consumption,indicating that the carbon source consumption was mainly used for the denitrification process.