The Denitrification Influence And Microbial Characteristics Of Solid/Liquid Carbon Source In Denitrification Biofilter

Water eutrophication is an urgent environmental problem in China.One of the main reasons for eutrophication was that excessive nitrogen is discharged into receiving water body by municipal sewage treatment plants.Under the circumstance of limited environmental capacity,the effluent of sewage treatment plants that meet the first B standard still imposes a great burden on the natural water environment,and the action of "upgrading the bid" is imperative.Total nitrogen is one of the key indicators restricting the upgrading of the standard.Total nitrogen is one of the key indicators restricting the upgrading of wastewater.The ratio of C/N in wastewater directly affects the efficiency of biological denitrification.Adding extra carbon source is the way to achieve the target of total nitrogen in low carbon source wastewater treatment plants.External carbon sources can be divided into liquid carbon sources and solid carbon sources,both of which have their own advantages,but most of the current studies are limited to denitrification performance of single solid-liquid carbon sources,and the results are not comparable with each other;direct comparison of denitrification effect of solid-liquid carbon sources and sludge yield is rare to quantify their performance.Therefore,in this study,liquid carbon source,solid carbon source and mixture of solid carbon source and ceramsite(1:1)were used as denitrification carbon source to compare and analyze the similarities and differences of denitrification effect,microbial community characteristics,sludge yield and carbon consumption between the two kinds of carbon sources.The main results and conclusions are as follows:(1)It was found that the residence time of liquid carbon source denitrification filter was less than that of solid carbon source denitrification filter when complete denitrification was the goal.The average nitrate concentration in effluent of liquid/solid carbon source denitrification filter is about 2 mg/L under different influent nitrogen concentration,and the nitrogen removal rate can reach more than 90%.When the influent nitrogen concentration is higher(more than 35mg/L),the mixed denitrification filter can achieve a higher removal rate with less PCL;furthermore,the relationship between influent nitrate concentration and residence time can be fitted by exponential function.The fitting equation of liquid carbon source denitrification filter is y=29.573e0.024 x,R2=0.994,solid carbon source denitrification filter is y=21.105e0.041 x,R2=0.997.The average nitrogen load of liquid carbon source denitrification filter is 0.68 gN/(Ld),which is higher than that of solid carbon source denitrification filter(0.52 gN/(Ld).The results show that the nitrogen load of liquid carbon source is greater than that of solid carbon source,and the denitrification capacity of liquid carbon source denitrification filter is higher than that of solid carbon source denitrification filter.(2)To explore the effect of residence time on denitrification,it was found that the shorter the residence time,the higher the nitrate concentration in the effluent of denitrification filter,and the worse the denitrification effect.When the residence time is short,the denitrification capacity of solid carbon source denitrification filter is less than that of liquid carbon source.When the residence time is long,the denitrification effect of solid carbon source can be the same as that of liquid carbon source,and the nitrate concentration of effluent is as low as 0-1 mg/L.Mixed denitrification filter,which reduces the dosage of solid carbon source PCL,can achieve the treatment effect corresponding to the dosage,or even exceed the dosage when the residence time is longer.The denitrification capacity of liquid carbon source denitrification filter is higher than that of solid carbon source denitrification filter and mixed denitrification filter.With the increase of residence time,the denitrification capacity of liquid carbon source denitrification filter decreases gradually,while that of solid carbon source denitrification filter and mixed denitrification filter increases gradually.(3)In order to explore the characteristics of microorganisms,high-throughput sequencing results showed that the depth of sequencing was sufficient,the microbial diversity of inoculated sludge S1 was the highest,and that of liquid carbon source denitrification filter S2 was the lowest.In the composition of microbial community,Proteobacteria,Bacteroidetes,Firmicutes,Actinobacteria and Chioroflex were the highest in the five samples at the level of phylum.In the comparison of microbial community in denitrifying filter,the similarity among three parallel samples of each sample was the highest.The species relationship between solid carbon source denitrification filter S3 and solid carbon source part S4 of mixed denitrification filter was the closest,and the bacterial species from S4 to ceramsite part S5 of mixed denitrification filter had certain transferability.The species distribution of solid carbon source S3-S5 and liquid carbon source S2 in denitrification system was obviously different,which is caused by the difference of carbon source types.With the acclimation of microorganisms,the microbial community of inoculated sludge S1 changed significantly.The denitrifying bacteria in S2-S5 denitrification system were enriched to varying degrees relative to S1.Flavobacterium,Thauera,norank_p_Gracilibacteria and Azospira were the main denitrifying bacteria in S2-S5.The proportion of bacterial species with higher abundance in S3-S5 was higher,among which Acidovorax was the most abundant in S3,Dechloromonas and Simplispira were the most abundant in S4 and Malikia was the most abundant in S5.(4)The carbon consumption per unit of the three reactors was 4.35 gCOD/gN,4.29 gCOD/gN and 3.83 gCOD/gN,respectively.The carbon consumption for biological assimilation accounted for 28%,28% and 18% of the total carbon consumption.Using solid carbon source to remove the same amount of nitrogen has a slight advantage.Reducing the use of PCL can reduce the unit carbon consumption to a certain extent.The sludge yields of the three reactors were 0.41 gMLVSS/gN,0.41 gMLVSS/gN and 0.49 gMLVSS/gN,respectively.The biomass growth in denitrification process may not be related to the type of carbon source.Reducing the use of PCL filler will increase microbial production and sludge yield.