| Activated sludge nitrification and denitrification is recognized as the most economical and effective sewage treatment method,and is widely applied in wastewater treatment plants for biological nitrogen removal of municipal domestic sewage and industrial wastewater.However,the traditional activated sludge process has poor stability in actual operation,which is prone to sludge bulking and sludge loss,and the separation effect is not enough,and the excess sludge production is high,which increases the cost of subsequent sludge treatment.The biofilm process has strong impact resistance,adaptable to the change of water quality and quantity,convenient operation and management,less energy consumption,and can effectively solve the problems of sludge bulking and poor stability in specific sewage treatment,which brings new choices for the sewage treatment industry.At the same time,because the problem of relatively low carbon and nitrogen in sewage,the secondary effluent of the wastewater treatment plant still contains high concentration of nitrate,which is difficult to meet the more and more stringent sewage discharge standards in China.In order to achieve the standard discharge,dissolved organic matter such as methanol should be added as carbon source in denitrification stage.Although the addition of liquid carbon source can improve the removal efficiency of total nitrogen to some extent,it significantly increases the operating cost,and it is easy to face organic pollution of effluent caused by excessive addition of carbon source.Therefore,the study of denitrification is of great significance.Here,we study the operational characteristics of the advanced denitrification process in the denitrification biofilm system,clarify the physicochemical characteristics of microbial metabolites(SMP),and reveal the mechanism of microbial community succession.It provides theoretical basis for further optimization of experimental conditions,determination of optimal parameters and improvement of effluent quality,which is helpful for the popularization and application of this technology in engineering.The main research contents and conclusions are as follows:1.The anoxic sequencing batch biofilm reactor(ASBBR)was built.The growth of microbial biofilm was made by adding suspension filler,and the domestication of denitrification biofilm was carried out.In the stable stage,the concentration of NO2--N and NO3--N in the effluent was 0.19±0.19 and 1.17±0.67 mg/L,respectively,and the removal efficiency of total nitrogen was 97.27±1.53%;in the whole operation cycle,the removal efficiency of nitrogen compounds and COD was 95.1% and 94.8%,in which N2 O accounted for 1.27% of total nitrogen removal;after the formation of biofilm,the content of EPS decreased from 52.5 mg/g to 27.5 mg/g,about 6.63 of PN/PS in TB-EPS of biofilm,is conducive to the stability of biofilm;the three-dimensional fluorescence parallel factor molecule(EEM-PARAFAC)data shows that the fluorescence intensity score of protein substances in SMP starts to decrease from 0.42 to 0.31 in the cycle,then increases to 0.39,and then decreases to 0.31 at the end of the reaction,humic acid is not easy to be degraded;high throughput sequencing showed that the abundance of Lysobacter,Tolumonas and Thauera increased by 23%,15.66% and 3.55% respectively.The enrichment of denitrification genes was realized.The enrichment of Lysobacter showed that there was autotrophic denitrification in this experimental system.2.Adding 40% polybutylene succinate(PBS)solid carbon source to anoxic tank based on the traditional A/O process to enhance denitrification can solve the problem of low total nitrogen removal efficiency caused by insufficient influent carbon source in the traditional process.After the formation of PBS biofilm,the removal efficiency of ammonia nitrogen did not change significantly,were 97.64 ± 1.82% and 98.86 ± 0.91%,respectively.Nitrite was always at a low level,and the removal efficiency of total nitrogen increased nearly 40%;The improvement of total nitrogen removal efficiency mainly occurred in the anoxic pool A1,and the nitrate content of A1 after reflux was only 18.9%;The PARAFAC data showed that at aerobic stage SMP fluorescence intensity scores showed an increasing trend before and after biofilm formation,the fluorescence intensity score of protein components in SMP increased from 0.36 to 0.41 before PBS was added in the anoxic stage,and decreased from 0.40 to 0.34 after PBS was added.However,the humic acid and fulic acid substances that were difficult to decompose showed irregular changes;The scanning electron microscopy(SEM)showed that the formation of biofilm provided clear evidence,and showed that PBS as an external carbon source had strong durability.Through high-throughput sequencing comparison of microbial community structure before and after change,it was found that the abundance of Spirochaetes and Chlorofloxi related to solid-phase denitrification in PBS biofilm and suspended microorganism increased by 45.11%,38.49%,10.89% and 3.26% respectively;The diversity of microbe had obvious change compared with that before adding,but the species diversity of microbe and suspended microbe in PBS biofilm had little difference.3.On the basis of heterotrophic denitrification system,sulfur autotrophic denitrification experiment was carried out.In order to provide electron donors and biofilm growth carriers for denitrifying bacteria,the single sulfur was added to the column reactor in SPBR.After 90 days of stable operation,nitrate removal efficiency and total nitrogen removal efficiency are as high as 94.87±2.22% and 93.15±2.76%;The average concentration of sulfate in the effluent is one 14.316±28.08 mg/L;The molecular weight of SMP is mainly distributed between 500-1000 Da,70000 Da high molecular weight organics are the intermediate products in the process of sulfur autotrophic denitrification;The fluorescence characterization of SMP in different heights and the data of PARAFAC show that the fluorescence intensity score is from the 0.15 increased to 0.53 in the height of 40 cm,and then gradually descend to the zero 0.22;The results of FTIR showed that SMP contained polysaccharide and protein,as well as amine,hydroxyl and carboxyl components;Compared with inoculated sludge,as the main sulfur oxidizing bacteria(SOB),Sulfurimonas,Thiomonas and Thiobacillus,SMP was transformed from 0.02%,0.07% and 0.03% to 8.73%,1.11% and 6.41% after 90 days of stable operation,PCA analysis and Bata diversity analysis showed that microbial community succession has reached a stable stage. |
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