| Total nitrogen pollution is one of the common water environment pollution,and with the increasing seriousness of total nitrogen pollution problem,the country has implemented more and more strict discharge requirements for total nitrogen water pollutants.Therefore,in order to effectively improve the environmental quality of receiving water bodies,it is necessary to study the deep denitrification treatment of discharged wastewater.For water bodies polluted by total nitrogen,biological nitrification denitrification process is generally used for removal.However,the lack of carbon source in polluted water bodies brings a big impact on the biological denitrification efficiency.In order to improve the efficiency of nitrogen removal,it is necessary to consider the addition of an additional carbon source to obtain the desired effect of nitrogen removal.Since most of the liquid carbon sources used are costly and difficult to control,natural solid carbon sources are gaining more and more attention because of their low cost and wide sources.However,the denitrification effect of natural solid carbon source alone is poor.In order to improve the denitrification efficiency,this paper constructs a coupled system of bamboo shavings and iron filings to enhance denitrification to achieve better denitrification effect.In this paper,static experiments were conducted in conical flasks to determine the best filler among wood shavings,bamboo shavings,rice husk and peanut shells,and different iron shavings mass dosing ratios were designed to determine the best combination of ratios.Three groups of denitrification devices were designed for dynamic experiments,No.1(bamboo shavings with iron chips),No.2(bamboo shavings)and No.3(ceramic pellets),to test the effect of changing the total nitrogen concentration of influent water and hydraulic residence time on denitrification of the coupled system.Finally,SEM and 16 s RNA were used to understand the utilization of filler and the community structure of microorganisms in the filler to investigate the mechanism of nitrogen removal in the coupled system.The following conclusions can be obtained from the above experiments.(1)In the static experiment,the four materials bamboo shavings had the best nitrogen removal effect,and the total nitrogen removal rate could reach 92.3% under the condition that the influent total nitrogen was 50 mg/L.The carbon release of bamboo shavings was slightly lower than that of wood chips,and the TOC concentration could reach 3.78 mg/L after stabilizing the effluent,and bamboo shavings were selected as the filler for the dynamic experiment under comprehensive consideration.(2)Five kinds of casting ratios of iron chips and fillers,0:1,1:4,1:2,3:4 and 1:1,were designed for static denitrification experiments,and the best denitrification effect was obtained from the experimental effect when the casting ratio of iron chips and bamboo shavings was 1:2.(3)In the dynamic experiment,the hydraulic retention time was 18 h,12h and 6h,the influent total nitrogen was 20mg/L,40mg/L and 60mg/L,and TP was 1.14±0.06mg/L.During the 120 d stable operation,the total nitrogen removal rate was 85.6±12.8% and51.1±20.3% for No.1 and No.2 respectively,No.1 total nitrogen removal was higher than No.2 67.8%,and its removal rate of total phosphorus was 74.7%,No.1 was 68.1% higher than No.2;both effluent COD was lower than the standard of "urban wastewater treatment plant pollutant discharge standard"(GB18918-2002)level A,but No.1 TOC release was 54.6% higher than No.2;the total iron release of the coupling system was stable,and the effluent total iron concentration was 0.26±0.09mg/ L,which is lower than the limit value of surface water environmental quality standard.No.3 has poor denitrification effect due to no carbon source intake.(4)Since column No.3 had no applied carbon source,the denitrification effect was poor and biofilm formation was less.Only No.1 and No.2 packing were extracted for electron microscopy scanning and 16 s RNA sequencing,and SEM characterization results showed that compared with No.2,the surface of bamboo packing in the coupled system was obviously adhered with many fibrous flocs,more sticky material and microorganisms,and the biofilm was more compact.16 s RNA test results showed that the coupled system had more microbial abundance and biodiversity;the bamboo filler bacteria in the two devices mainly consisted of Phylum Aspergillus,11.2～12.9% of Phylum Bacteroides and11.3～12.3% of Phylum Actinomycetes,and the dominant phylum was both Phylum Aspergillus,accounting for 66.5%(No.1)and 49.7%(No.2),respectively;in the Phylum Aspergillus,the two bacterial groups were different,and the dominant genera were Pseudomonas spp.(No.1)and Thermomonas spp.(No.2),but the coupled system had more categories of denitrifying bacteria with the percentage. |
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