Study On The Nitrogen Removal Performance Of Short-cut Nitrification And Denitrification Coupled With Sludge Fermentation Process For Landfill Leachate Treatment

Landfill is the main way of municipal solid waste disposal in China,which leads to a large amount of leachate to be treated urgently.However,the characteristics of landfill leachate,such as high ammonia nitrogen content,low C/N ratio and high alkalinity,lead to the problems of high aeration energy consumption,high carbon source dosage and high treatment cost.Short-cut nitrification and denitrification technology is a very promising biological nitrogen removal technology.Because it can shorten the reaction process,control the nitrification in the stage of nitrotation and save part of carbon source.At the same time,it can reduce the aeration density and ultimately improve the reaction rate and total nitrogen removal with low energy consumption and high efficiency.However,in the treatment of aged landfill leachate,there are still some urgent problems to be solved,such as high concentration of free ammonia（FA）inhibiting nitrification process and insufficient carbon source for denitrification.Based on this,a short-cut nitrification and denitrification system for aged landfill leachate was constructed,and the rapid start-up of the system was realized by controlling the dissolved oxygen（DO）conditions.The effect of nitrogen removal of the system was optimized by step-feeding strategy,which reduced the inhibition effect of FA on ammonia oxidizing bacteria（AOB）,increased the nitrification rate,increased the abundance of AOB and total nitrogen load of the system.Then,free nitrite acid（FNA）,the product of short-cut nitrification,was used to enhance the hydrolysis of waste activated sludge to provide carbon source for denitrification process,so as to reduce the cost and improve the effect of nitrogen removal.Finally,the nitrogen removal effect of short-cut nitrification process coupled with sludge fermentation and denitrification technology was studied,and the optimal sludge addition ratio and reflux ratio were determined.The main results are as follows:（1）When the DO concentration was controlled below 1.0 mg·L^-1,the short-cut nitrification and denitrification system was successfully started,and the accumulation rate of nitrite nitrogen（NAR）was about 80%.The activity of nitrite nitrogen oxidizing bacteria（NOB）was inhibited under low DO condition,and the nitrous oxidation rate（NOR）was only0.78 mg·（L·h）^-1.Through the analysis of the water quality indexes along the system,it was found that the high alkalinity and ammonia nitrogen concentration of the aged landfill leachate led to high FA concentration in the O1 and O2 pools of the aerobic unit.The high FA concentration not only inhibited the NOB,but also inhibited the AOB activity,which reduced the nitrotation rate of the system.（2）The step-feeding operation reduced the substrate and FA concentration of the aerobic short-cut nitrification unit.Therefore,it reduced the inhibition of FA on AOB,increased the system nitrification rate and increased the total nitrogen volume load（NLR）of the system by23.53%.At the same time,the relative abundance of Nitrosomonas belonging to the genus of AOB in the aerobic unit O1,O2,O3 and O4 pools of the aerobic unit increased by 12.37%,68.57%,57.14%and 59.30%,respectively.External carbon source was used to optimize the denitrification effect.The results showed that when C/N=6 and the nitrification liquid reflux ratio was 300%,the total nitrogen removal rate（NRE）of the system reached 90.55%.（3）FNA pretreatment can promote sludge cracking and hydrolysis fermentation,increase carbon source production and improve denitrification capacity of the system.The results showed that FNA pretreatment increased the dissolution of organic matter.Under the condition of FNA=2.11 mg·L^-1 and treatment time of 12 h,the total organic carbon（TOC）content of sludge supernatant reached the highest of 1988 mg·L^-1,which was 91.36%higher than that without FNA treatment.With the increase of FNA concentration,soluble polysaccharide and protein content increased significantly.The soluble protein and polysaccharide content reached 375.31 mg·L^-1 and 73.10 mg·L^-1,respectively under the condition of FNA=2.11 mg·L^-1.FNA treatment changed the cell structure of sludge microorganism from compact type to loose type and resulted in cell hydrolysis.Meantime,FNA treatment reduced the size of sludge and increased cell decay rate,which was beneficial to sludge fermentation.In addition,FNA pretreatment can improve the utilization rate of internal carbon source and denitrification efficiency in the denitrification process with sludge fermentation.（4）The system of short-cut nitrification coupled with sludge fermentation process achieved efficient removal of pollutants from leachate.The combination of short-cut nitrification and denitrification with waste activated sludge hydrosis unit improved the utilization rate of internal carbon source and denitrification effect.Under the condition that the optimal sludge ratio（residual sludge dosage:water inflow）was 2:10,the NRE of the system is increased from 48.07%（no sludge pretreatment unit）to 78.48%.The optimal ratio of nitrification liquid reflux was 300%,and the NRE of the system was 88.27%under this condition.