Study On Nitrogen Removal Efficiency And Mechanism Of Three Kinds Of Crop Straw Fillers In Treating Low C/N Domestic Sewage

In recent years,due to the influence of living habits and incomplete rainwater and sewage diversion,domestic sewage in China generally shows the characteristics of low carbon to nitrogen ratio,and the lack of carbon source leads to incomplete denitrification,thus affecting the nitrogen removal effect.The existing sewage denitrification process needs to invest a lot of additional carbon sources,which has some disadvantages,such as high operating cost,poor denitrification effect,and easy secondary pollution of effluent.Therefore,how to find an efficient,energy-saving and low-cost denitrification process has become a key problem to be solved urgently for low C/N domestic sewage.In this study,domestic sewage with low C/N was taken as the target water body,and the biological aerated filter reactor was simulated to explore the denitrification performance and superior efficiency of ramie stalk,sorghum stalk and cotton stalk as three new crop straw fillers compared with polypropylene suspended fillers and traditional zeolite fillers.At the same time,the overall growth status,community structure and related dominant flora of microorganisms in each filler were analyzed,and the denitrification mechanism of different fillers was analyzed from the micro level,in order to continuously develop crop straws with low price and superior performance.The main conclusions of this paper are as follows:（1）By comparing the contents of C and N elements in three kinds of crop straw fillers with the static carbon release test,it is found that ramie stalk has the highest content of C element and the lowest content of N element,which has the greatest carbon release potential.In the static carbon release test of each filler,the carbon release law of the three crop straw fillers is basically the same,and the carbon release rate is in the order of K_{sorghum stalk}>K_{ramie stalk}>K_{cotton stalk}.The carbon release amount and carbon release duration of sorghum stalk are significantly higher than those of ramie stalk and cotton stalk,and its carbon release performance is stable,so it is a good solid slow-release carbon source filler.（2）Under the condition of low C/N,the sorghum stalk biological aerated filter reactor has the best nitrogen removal efficiency,with the average purification rate of nitrate nitrogen as high as 93.897%,the average concentration of nitrate nitrogen in effluent only 1.442mg/L,the average purification rate of TN 76.224%and the average concentration of effluent 13.645 mg/L;Ramie stalks and cotton stalks have higher ammonia nitrogen purification efficiency,with average purification rates of 98.946%and 97.833%respectively.Except for the suspended packing group,nitrite nitrogen did not accumulate in the other four groups of reactors,and nitrate nitrogen was the main component of effluent,so the nitrogen removal efficiency of sorghum stalk biological aerated filter reactor was the best.SEM results also confirmed that compared with zeolite and suspended filler,the lignocellulose structure on the surface of crop straw filler was easily destroyed by microorganisms.By breaking the functional groups and chemical bonds of lignin,hemicellulose,cellulose and other difficult-to-degrade macromolecules in it,the decomposition of crop straw was realized,and the pores on the surface of the filler were increased,which was more conducive to the attachment and growth of microorganisms.Therefore,compared with zeolite and suspended filler,the biofilm of crop straw filler grew more evenly and compactly,and was more suitable as an electron donor for denitrification.（3）In order to further reveal the denitrification mechanism of crop straw filler,microbial community structure in five groups of filler reactors was analyzed by microbial sequencing technology.The results showed that the microbial abundance in the crop straw packed reactor was significantly higher than that in zeolite and suspended packed reactor,and the microbial community diversity was richer,and the proportion of Proteobacteria was higher.Among them,the proportion of Proteobacteria in the sorghum stalk reactor was the highest,accounting for 58.202%.In addition,because of its unique internal structure and function,different fillers have great differences in enriched microbial communities.The dominant genus in sample A is Bacillus,the dominant genus in sample B is SC-I-84,the dominant genus in sample C is Denitratisoma,the dominant genus in sample D is A4b,and the dominant genus in sample E is Nitrospira.Compared with inorganic fillers,The dominant bacteria related to nitrogen removal in the reactor account for a higher proportion,and the biological nitrogen removal efficiency is also better.However,because the dominant bacteria in different reactors are different,the enriched microbial community is quite different,so the purification effect of various types of nitrogen is different.