| As an efficient wastewater treatment technology, Biological Aerobic Filter hasbeen applied widly in wastewater treatment and reusing area in recent years.Focused on the existing defects of BAF, a new kind of functional media,Na-pretreated zeolite, was developed. And on the basis of preparation of this newfunctional media, the serries experimental study and mechanism analysis, whichincluded the treatment efficiency and mechanism of Na-pretreated zeolite BAF,nitrification characteristics, denitrification characteristics of two stage Na-pretreatedzeolite BAFs under aeration and limited aeration operating mode, phosphorusremoval characteristics of Na-pretreated zeolite BAF with chemicals dosing on siteand of two stage Na-pretreated zeolite BAFs under alternating aeration operatingmode, treatment efficiencies of chemical enhanced two stage Na-pretreated zeoliteBAFs treating domestic sewage and optimal control strategy of back-washing inNa-pretreated zeolite BAF were carried out in this paper.The characterization of Na-pretreated zeolite media which have been preparedby roasting followed with soaking in NaCl solution was of good properties ofammonia adsorbing and ion exchanging. And the treatment efficiencies of BAFswith natural clinoptilolite, ceramist and Na-pretreated zeolite media wereinvestigated respectively. The results indicated that Na-pretreated zeolite BAF hadhigher treatment efficiencies of SS, COD and ammonia than the other two BAFs intreating simulated domestic wastewater and the effluent quality was more stable.To illustrate mechanisms of pollutants removal in Na-pretreated zeolite BAF,The filtration equation based on coupled function of physicochemical andbiochemical process was constructed by using the methods of microelement analysisand mathematics modeling. And the parameters of filtration equation were fittedexperimentally and revised. So the synergetic purification mechanism ofphysicochemical and biochemical process in Na-pretreated zeolite BAF wasrevealed quantitatively. Structure of biofilm and distribution of microorganismpopulation in Na-pretreated zeolite BAF was analyzed experimentally. And thebiological analysis results corresponded with the general rules revealed by abovefiltration equation too.Nitrification properties of start-up and steady running period in Na-pretreatedzeolite BAF were investigated respectively. The results of parallel studies indicatedthat biofilm colonization rate of Na-pretreated zeolite BAF was much faster andnitrification efficiency was better than ceramist BAF. And the effluent quality ofNa-pretreated zeolite BAF was more stable and the ability of resisting shock loading of this reactor was much stonger too.Nitrous nitrification were also observedobviously in Na-pretreated zeolite BAF. When influence factors such as influent pHvalue, Do and filtration rate was controlled to6.5to7,1.0to1.5mg/L and5m/hrespectively, the nitrite accumulation rate of Na-pretreated zeolite BAF can keep at65%to75%stably. The nitrite accumulation rate could also reach50%or more byadding sodium hypochlorite intermittently.The experimental results of denitrification efficiency in Na-pretreated zeoliteBAF showed that the average removal rate of TN in single stage Na-pretreatedzeolite BAF was only about35%. Denitrification efficiency could be improved to60%by adopting a two stage Na-pretreated zeolite BAFs which included a carbonremoval BAF reactor and a nitrogen removal BAF reactor with anoxic zone wasbrought forward. When hydraulic retention time(HRT) of the two stageNa-pretreated zeolite BAFs system was greater than one hour, the influence of HRTon the TN removal of the two stage system was insignificant.The optimal gas-waterratio for the two stage Na-pretreated zeolite BAFs in this study was5:1.The phosphorus removal characteristics of Na-pretreated zeolite BAF wasinvestigated too. The results indicated that average removal rate of TP in singlestage Na-pretreated zeolite BAF was only about20%.The Na-pretreated zeolite BAFwith ferric and aluminum salt dosing on site was of good phosphorus removalefficiency，which can improve the removal rate of TP with77%. The enhancedperformanc of ferric salt dosage on phosphorus removal was better than aluminumsalt dosage. When the chemical dosing ratio was less than1.5(phosphorus:chemicalflocculants), the dosage of chemical flocculants on site had slight influences on theremoval efficiency of SS and COD, nitrification efficiency, head loss and runningperiod of Na-pretreated zeolite BAF.Through setting two stage Na-pretreated zeoliteBAF reactors with aerating alternately, perfect phosphorus removal effect could beobtained. The optimal alternate aerating time was12hours in this study. Under thisoptimal alternate aerating time, the average phosphorus removal rate of two stageNa-pretreated zeolite BAFs was83.9%and the average concentration of TP ineffluent was1.04mg/L.A novel combined process which includes an aerating filter with chemicalflocculants dosing on site and a limited-aerating filter with an anoxic zone settingwas put forward in this paper and its’ treatment efficiency to domestic sewage wasconfirmed to be very good. When filtration rate was1.5m/h, gas-waster ratio of thefirst stage BAF was5:1and of the second stage BAF was3:1, FeCl3dosing ratiowas1.5and water temperature was23~28℃, the meaning removal efficiency of SS,COD, NH3, TN and TP of the combined process were94.1%,94.2%,94.9%,62.1%and92.9%respectively. The effluent quality meet the requirement of nationalstandard of non-drinking domestic using water(GB/T18920-2002). To ensure the backwashing effect and maintain the stable removal efficiency ofNa-pretreated zeolite BAF, the optimal controlling strategy and backwashingprocess of Na-pretreated zeolite BAF was suggest as follows: Firstly, gasbackwashing only for3min with gas wash rate of10L/(m~2·s). Secondly, gas andwater backwashing together for3min with both wash rate of10L/(m~2·s). Finally,water backwashing only for9min with water wash rate of10L/(m~2·s). |
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