Deep Nitrogen Removal Technology Using Organic Matter In Soybean Processing Wastewater As Electron Donor

At present,in the process of urban domestic sewage treatment,the concentration control of total nitrogen（TN）in tailwater has been paid more and more attention.In order to reduce the total nitrogen concentration in tailwater,many urban sewage treatment uses three-stage nitrogen removal process.By adding organic carbon source as electron donor,NO₃^--N in the tail water can be reduced to reduce the total nitrogen concentration.The commonly used additional carbon sources mainly include methanol and sodium acetate.Additional carbon sources often lead to higher wastewater treatment costs.Therefore,cheaper organic carbon sources are sought as electron donors to reduce TN concentration in tailwater.Among them,soybean processing wastewater is a potential organic carbon source.Soybean processing wastewater is a kind of high concentration organic wastewater,and contains rich resources,such as protein,amino acids,lipids and sugars.If the traditional method is used for processing,it wastes potential resources,increases the cost of purchasing carbon sources,and consumes power.If the soybean product processing wastewater is used as an electronic donor,it not only reduces the cost of wastewater treatment,but also realizes the resource utilization of soybean product processing wastewater,but also makes the wastewater effectively treated and reduces the pollution to the environment.In this study,the self-made soybean milk simulated soybean product processing wastewater was used as the electron donor for denitrification of NO₃^--N with an initial concentration of 30 mg N/L,and the TN concentration was reduced to less than 5 mg N/L through two stages of denitrification and nitrification alternately.It was found that the NH₄⁺-N released in the wastewater from soybean processing mainly comes from the amino acids in it.The amino acids were then used as electron donors for denitrification,which also alternated between secondary denitrification and nitration,resulting in a total nitrogen concentration of less than 5 mg N/L.Finally,Rhodococcus ruber was used to accelerate the denitrification of soybean processing wastewater as electron donor through bioaugmentation.The specific research process and results include:（1）Using soybean milk to simulate soybean product processing wastewater as electron donor,TN concentration can be reduced to below the effluent standard of 5mg N/L through the alternation of two-stage denitrification（AN）+nitrification（OX）.The effects of soluble COD and solid COD on denitrification in soybean processing wastewater were discussed,and their effects on denitrification rate were compared.The results showed that the rate of soluble COD was faster than that of solid COD.When both are used as electron donors,the denitrification rate is faster.In AN,Dechloromonas and Brooklawnia utilize only soluble COD,while Paludibacter and Christehsenellaceaue can hydrolyze solid COD and use it as an electron donor to drive denitrification.（2）Nitrogen in amino acids is the main source of nitrogen in soybean processing wastewater.Subsequently,glutamic acid,isoleucine and methionine were selected as electron donors for denitrification respectively,and the denitrification was driven in the anoxic phase of the two-stage denitrification（AN-1）+nitrification（OX-1）process,which could control the released NH₄⁺-N concentration at a low level.The results show that amino acids possess sufficient internal electrons for the reduction of nitrogen and more than 60%of internal electrons for the reduction of exogenous nitrate.It can be seen that amino acids can also be used as electron donors for denitrification.Therefore,when soybean product processing wastewater is used as a carbon source for denitrification,there is no need to worry about TN exceeding the standard.In this process,high-throughput sequencing analysis of denitrifying sludge showed that denitrifying bacteria were mainly enriched in AN-1 and nitrifying bacteria were mainly enriched in OX-1.The decarboxylation of amino acids occurred in the nitrification stage,Denitratisoma played a role in the reduction of NO₃^--N,and Nakamurella played an important role in the biodegradation of amino acids.（3）Soybean processing wastewater contains many resources and can be used as an electron donor for denitrification.In order to accelerate the denitrification of soybean processing wastewater as electron donor,Rhodococcus ruber was used for bioenhancement to accelerate the denitrification process.Compared with ordinary acclimated denitrification sludge,the addition of R.ruber can increase the removal rate of NO₃^--N by 20%.The related principle is that R.ruber can quickly release electron donors from the substrate,thus speeding up the denitrification rate.When soybean processing wastewater was used as electron donor,the NO₃^--N,TN and DOC removal rates of bioenhanced denitrification using R.ruber were superior to those of acclimated sludge using soybean milk to simulate soybean processing wastewater.Genome sequencing analysis showed that R.ruber contains the complete pathway enzymes for the metabolism of galactose,glycogen,vitamin B₆ and isoleucine.R.ruber can also metabolize amino acids completely under the action of various enzymes.The intermediate products in the metabolic process can be used as electron donors,thus increasing the denitrification rate.