Study On The Performance Of Multi-media Filtration Technology For Tertiary Treatment Of Secondary Effluent From Urban Sewage Treatment Plant

The secondary effluent comes from the urban sewage treatment plant which contains soluble refractory organics,nitrogen,phosphorus and other soluble inorganic compounds;they all have bad effects on the natural surface water.In order to maintain the ecological balance and enhance the retrieval and utilization of weastwater,many municipal sewage treatment plants are facing upgrading,especially in Beijing,the effluent from the sewage treatment plant needs to meet the IV standard（GB3838-2002）of the surface water.At present,the conventional physiochemical tertiary treatment has high operation costs,but the removal ability of soluble organic matter and inorganic nitrogen and phosphorus in weastwater is not good.Therefore,it is of great significance to explore the economic and efficient tertiary treatment to improve the ecological environment and save water resources.Take the IV standard of surface water as target,this paper constructe a multi-media filtration-ion exchange system for tertiary treatment of secondary effluent,and examine the performance of this system.This study selects the zeolite and activated carbon as filter materials of the multi-media filter.The static experiment shows that,the adsorption processes of zeolite and activated carbon followed Freundlich adsorption isotherm,and the adsorption kinetics conforms to the quasi two order kinetic equation.The dynamic experimental result shows that the multi-media filtration has good removal effect on ammonium nitrogen（NH₄⁺-N）、chemical oxygen demand（COD）and turbidity,the effluent concentration of NH₄⁺-N and COD can meet the IV standard（GB3838-2002）of the surface water,the turbidity can meet the requirements of the water landscape.However,the total nitrogen and total phosphorus of the filter effluent can not meet the standard,need for advanced treatment.The filter layer’s configuration greatly influences the efficiency of the tertiary treatment of the secondary effluent.According to the water quality of the secondary effluent,when the filtration rate was 5 m·h^-1and both of the zeolite layer and the active carbon layer are 45 cm thick,the filtration cycle can reach34 h.The average removal rates of COD,NH₄⁺-N,total nitrogen（TN）and turbidity in the cycle are 36.3%、90.9%、71.6%and 61.7%respectively,and the water head loss of the whole filter layer is only 1.65 cm·h^-1.The mud content of the filter material at the bottom 15 cm of the filter layer is about 1.17%,which is several times of the conventional quartz sand,indicating that the filter materials has a strong ability to absorb suspended matter.The filter material was cleaned by means of gas-water backwashing.The strength of gas flushing is 15 L·m^-2·s^-1,the air backwashing time is 2 min;the water backwashing strength is 10 L·m^-2·s^-1,the washing time is 5 min.After the washing,the amount of the suspended matter intercept by unit mass filter material reduces to about0.1%.Compared with ordinary quartz sand filter material,less water is used for backwashing.The adsorbed saturated zeolite and activated carbon are firstly regenerated with NaCl and NaOH mixed solution for 2 hours,and then regenerated with methanol solution for 3 hours.The regeneration rate of the regenerated zeolite is greater than 90%,and the regeneration rate of activated carbon is greater than 70%.Comprehensive investigation the ability of ion exchange resin to remove nitrogen and phosphorus,the ability to resist the interference of other anion and the effect of multiple regeneration of the resin,we chose D201 as the filling resin for ion exchange equipment.The optimum water production rate was 50 BV·h^-1,and the water production volume of the ion exchange device could reach 500 BV.In the resin regeneration experiment,the resin was dynamically regenerated with 5%NaCl and 1%NaOH mixed solution.By investigating the concentration of TP and nitrate nitrogen（NO₃^--N）in the effluent of the regenerated process,the amount of regeneration solution should be 15 BV,and the corresponding regeneration time should be 1h.Taking a filtration cycle for example,the tertiary treatment efficiency of the multimedium filtration and ion exchange system for secondary effluent was investigated.The results showed that in a filtration cycle the ion-exchange unit was produce 1700 BV reclaimed water,and the average removal rates of COD,NH₄⁺-N,TN and TP were 45%,92%,95%and 83%respectively.The effluent can meet the IV water quality standard of surface water.Turbidity can meet the requirements of landscape water reuse.Through economic analysis,it is proved that the process has certain feasibility,and it can provide relevant data support for the upgrading of urban sewage treatment plants.