| In order to increase the contaminant removal ability of wastewater treatment plants,many researches focus on the improvement of the removal ability of biochemical treatment unit while only few researches aim at the sand removal unit in the pretreatment process.However,with the popularization and application of oxidation ditch,A2/O and other sewage treatment technologies which usually cancel of surpass the primary sedimentary tank for the insurance of sufficient carbon resources for nitrogen and phosphate removal,the sand basin becomes the only sand removal unit in the entire sewage treatment process.The residual fine sand after the sand basin has brought serious influences to the normal operation of sewage treatment plants.Therefore,the improvement of sand removal ability of sand basin in oxidation ditch and other sewage treatment processes without primary sediment tank is of great significance to the stable operation of sewage treatment plants.Since the 1990's,with the introduction of foreign technologies,vortex-type grit chamber has become the most common grit chamber in sewage treatment plants in China.However,after a lot of field investigations,we found that problems like low removal efficiency,high content of fine sand in the overflow water of grit-water separator commonly exist in the operating vortex-type grit chamber.The present study targeted on the ge treatment plant in Chongqing and investigations were focused on operational processes of the grid sedimentation,grid lift and grit-water separation of the vortex-type grit removal system.Diagnosis were made after field investigations,and technical improvement measures were raised focused on each operational processes.A new type of grit-water separator was designed based on the catch of organic matters and the improved removal of fine grit.Main researches and their results in the present study were shown below:(1)By field investigation,testing and analysis,this study found out the following problems: the separating area of the tested vortex-type grit chamber had insufficient rotation condition and bad sand precipitation effect;the air lift device had low capacity of grit carrying and high air volume in the mixture,and grit-water separator had low grit production,while the overflow water had plenty of fine grit.(2)The technical renovation measures for the vortex-type grit chamber mainly include: set an opening cone plate at the separating area and add a jet pipe using recycled water;change the original sand tube from DN110 to DN140,which is increased from 2.4:1 to 2.9:1;install an air exhausting device at the beginning of the separator and step feed is adopted,move the overflow weir from the back to the side of the tank,set a V-baffle in front of the inlet pipe and a U-deflector between the axial spiral and tank.(3)By reconstruction,the removal efficiencies of grit,COD and SS were raised to 2.2 and 2.48 times of the original,respectively.In term of the particle size,the removal efficiencies of particles >200?m and 100-200?m were respectively raised to 1.37 and 2.92 times of the original,and the removal efficiency of particles <100?m was nearly zero.(4)An integrated XPSF grit-water separator was designed and developed to enhance the removal of fine grit and improve the organic matters(COD)in effluent.The trial in a sewage plant in Chongqing made stage progress,where COD and SS in the effluent were 332 and 167 mg/L respectively,and the grit removal efficiency was raised to 550kg/d.Compared to LSSF grit-water separator,reducing COD intercept,SS and increase grit content were promoted 2,1.2 and 2 times,and especially the removal efficiency of particles 100-200?m was promoted 4 times. |
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