Study On Characteristic Of Removal Of Nitrogen By Coupling Carbon Release And Biological Oxidation Of Walnut Shell Based Filler BAF

Water is the source of life.Good water quality is one of the basic guarantees for human survival.However,according to the?China Environment Status Bulletin 2016?,there is still deterioration of water quality in some parts of China,among which ammonia nitrogen is one of the major indicators for monitoring the surface water and the groundwater quality.Removal of ammonia nitrogen from the water body and purification of water quality cannot be delayed.At the same time,the output of walnut shells in China is large,and the utilization of walnut shells is far-reaching in the contemporary meaning of resource shortage.Therefore,the utilization of walnut shells for treating ammonia nitrogen in wastewater fully reflects its ecological and environmental significance.China is also a big producer of leather.The tanning industry has also brought about more and more urgent environmental problems while promoting economic development.Ammonia nitrogen is also one of the main pollutants in the wastewater of the tanning industry.In recent years,although the treatment of ammonia nitrogen in wastewater from tanning industry has made great progress,the removal of total nitrogen in the tanning industry has become the focus of attention with the control of total nitrogen pollution by the Chinese government during the 13th Five-Year Plan period.In this study,in order to remove ammonia nitrogen and total nitrogen from the waste water produced by the tanning industry,walnut shells frow Xinjiang were used as the research object,and the physicochemical characteristics of walnut shells were observed using ESEM and infrared spectrum analysis.Combined with long-term and short-term leaching organics tests,static denitrification tests,and static and dynamic adsorption tests,the characteristics of organic carbon released from walnut hulls and adsorption characteristic of ammonia nitrogen were revealed.The walnut shells,ceramsites and zeolites were respectively combined in 1:1 to construct four types of fillers BAF:W-BAF,C-BAF,CW-BAF and ZW-BAF.The target of treatment is the simulated leather waste water containing some pollutants such as ammonia nitrogen and total nitrogen and so on.To investigate the removal efficiency of pollutants from various reactors under different hydraulic retention times;Furthermore,the removal characteristics of the main pollutants and nitrogen conversion characteristics of the four fillers BAF along the different heights of the filters were further analyzed and compared.The denitrification characteristic of the Walnut shells based filler BAF was clarified.Finally,through the electron microscopic observation,biomass and bioactivity tests of biofilms along the four fillers,combined with Biolog-ECO technology,the microbiological metabolic fingerprints and carbon source utilization efficiency of biofilms along four fillers were identified to clarify microbial metabolism activity and microbial community diversity.The main results of the study are as follows:?1?It has the highest content of holocellulose in the walnut shells from Xinjiang,followed by lignin and polypentose.The short-term clean water leaching of organic carbon and denitrification tests show that the walnut shell is stable in the structure,high in carbon release and suitable as a solid carbon source with supporting.The carbon release long-term test shows that the release of organic matter per unit of walnut shell is a release attenuation every day.The release of carbon from 0 to 3 days is a rapid decay period,the release from 4 to6 days is a moderate decay period,6 to 12 days are a slow decay period,and it is a gradual stabilization period after the 12th day.The trend curve is y=4.7221x^-0.893.?2?ESEM observation shows that the surface structure of the walnut shells is dense and the micropores are numerous and transparent.The pore distribution is very regular,showing isotropy having a larger total pore area and porosity.In addition,the walnut shell has a certain degree of adsorption performance with-OH and other functional groups on the surface.The static adsorption of ammonia nitrogen in the walnut shells is a spontaneous endothermic process with single-layer and multi-layer adsorption mainly based on physical adsorption.The dynamic adsorption process is in accordance with the Thomas adsorption kinetics model.The adsorption equation is y=-0.0063x+2.1488,R²=0.9769.?3?The four filler BAFs have different lengths of the film formation.With COD removal efficiency stable at 80%,the W-BAF membrane preparation takes about 20 days,while the C-BAF requires about 15 days,and the combined filler BAF needs about 17 days.However,measured by the ammonia nitrogen removal efficiency of 60%,the W-BAF incubation time is less than the other three types of BAF,which takes 15 days,the C-BAF takes about 18 days,and the combined filler BAF takes about 12 days.During the stable operation stage of BAF,HRT had few effects on COD removal from walnut shells and its combination BAF.HRT=12h,8h and 6h,the COD in effluent of all four kinds of filters was less than 20 mg/L,and the removal efficiency were all between80⁹0%.HRT has a greater impact on the removal of ammonia nitrogen,and the removal efficiency of ammonia nitrogen generally decreased with the decrease of HRT.The strong denitrification in the combined fillers filter makes the removal efficiency of TN higher than that of a single filler filter.The C-BAF has a poor removal effeciency on TN.?4?Four kinds of filler BAF have rich biomass along the influent side and less biomass at the water outlet side.The biological activity is high below the40cm height of the filter,close to the outlet,the biological activity is reduced.The removal of COD?ammonia nitrogen and total nitrogen mainly occurs in the lower part of the filter,and the removal effect is generally weak along the flow direction and far from the water inlet end.The nitrogen conversion characteristics of the four types of filler BAF are different,and the denitrification characteristic is also different.Ammonia-nitrogen concentration in the W-BAF is decreased linearly along the water flow direction,and nitrate nitrogen production was low,nitrite was accumulated.What's more,DO content was low,and TN removal efficiency was higher,which can be judged that short-cut nitrification and denitrification occurred.The nitrite nitrogen accumulation in C-BAF is nearly zero.The removal of ammonia nitrogen in the lower region of the filter tank is dominated by nitrification-denitrification,while the upper region is dominated by nitrification.The accumulation of nitrite nitrogen in CW-BAF is relatively small.The carbon source released from the walnut shells increases the activity of denitrifying bacteria.The ammonia nitrogen is converted to nitrate nitrogen.Therefore,the removal of ammonia nitrogen mainly depends on carbon release,nitrification and denitrification.The characteristic of nitrogen removal by ZW-BAF is mainly due to the ion exchange adsorption of zeolites and the coupling of carbon release,nitrification and denitrification of walnut shells.The Biolog-ECO method shows that the biofilm microorganisms in the four filler BAFs have higher utilization rates of sugars and derivatives carbon sources and lower utilization rates of amine and alcohol carbon sources.W-BAF fillers had the highest number of microbially available carbon sources along the biofilms,followed by ZW-BAF and CW-BAF,and C-BAF was the least.The overall homogeneity of the filler material affects the uniformity of the microbial attachment distribution.The combination of different types of fillers is more conducive to the diversification of microbial species in biofilms than the single fillers,which can complement the insufficiency and to a certain extent can maintain the stability of the BAF system and improve the efficiency.Utilizing walnut shells to remove nitrogen from waste water and treating them with waste,the abandoned nitrogen-rich walnut shells can be further used in land recycling or composting,which not only provide new ideas and the new?green?approach for the removal of nitrogen from tannery wastewater to promote the sustainable development of the tanning industry,and it will also have positive significance for agricultural and forestry wastes to give full play to their potential value and expand their application in the field of environmental protection.