Performance And Mechanism Of Strengthening Nigrogen Removal By Up-flow Microaerobic-oxic Process

The national12thFive-Year Plan on urban sewage treatment and recyclinginfrastructure construction clearly stated that we should further increase the capacity ofwastewater treatment plants （WWTPs）, speed up the sewage treatment plant upgradingand reconstruction, and improve the function of nitrogen and phosphorus removal. As aconsequence, nitrogen and phosphorus removal is still the challenge to be urgently solvedin the WWTPs. The innovation of new process and techonogies for strengthening nitrogenand phosphorus removal is becoming the focus of research.A novel process, up-flow microaerobic-oxic （M/O） process, for strengtheningbiological nitrogen removal on a laboratory scale was proposed which is consisted of anup-flow microearobic column reactor and an oxic reactor to treat the real domesticwastewater. The up-flow microaerobic reactor is the key unit and integrated theadvantages of micro-aerobic environment and upflow condition. Micro-aerobiccircumstantce is benefit to microorganism diversity which is helpful to many nitrogenremoval pathways such as simultaneous nitrification and denitrification （SND）, shortcutNitrification-denitrification. Upflow condition could form the dissolved oxygen （DO）concentration and mixture liquor suspended solid （MLSS） gradients which contribute toresistance of loading shock. As a result, this new process created necessary conditions forstrengthening biological nitrogen removal.In this thesis, the performance of M/O process under different sludge age, hydraulicretention time （HRT） and Internal return ratio （r） was investigated with demesticwastewater. The optimal operating condition was obtained that sludge age was25d, HRTwas12h, and interal return ratio was200%. Under these conditions, the average removalefficiencies of chemical oxygen demand (COD_Cr), ammonium nitrogen （NH4+-N）and totalnitrogen （TN-N） were88.3,66.5, and91.8%with effluent concentrations of COD_Cr,TN-N and NH4+-N of22.8,2.7and16.9mg/L, respectively. The process ran stably and theactivated sludge performed well even when the influent loading varied greatly.Comparision of performance and mechanims between M/O and A/O processes in terms of pollutant removal and the stabllity of reactor was conducted by controlling thesame operation conditions.The result showed that the M/O process was higher15.5%thanA/O process in terms of average removal efficiency of total nitrogen. This phenomenonexisted in up-flow microearobic column reactor and oxic reactor. M/O process has theadvantages of more stable performance and better resistance to the load shock than theconventional A/O process.Investigated the characteristics of microearobic column reactor, we found that therewas sludge concentration gradients along the column reactor height, the MLSS is10g/Lat bottom of microearobic column. Micro-earobic column could change the constituent ofCOD_Cr, improve F/M of influent, and promote using efficiency of carbon. The distributionof sludge particles diameter was measured, the particle diameter ranged in0μm to500μm,mean diameter was about230μm at the same time. So there was dissolved oxygen （DO）gradients within activated sludge flocs, it was good for occurring many novel biologicalreactions of nitrogen removal in this circumstances.