Metallic Oxide Media Biological Aerated Filter For Domestic Wastewater

Biological Aerated Filter is an attractive wastewater treatment process with theadvantages of small occupation space, high efficiency and easy operation. It has been a hottopic in the wastewater treatment field. As the carrier of filtration and biofilm of BiologicalAerated Filter, filter media has an important influence on its operation efficiency. It will bewith great theoretical value to take deeply research on the filter media with specificperformances for the widespread use of BAF.The steel slag metallic oxide media and blast furnace slag metallic oxide media, whichhad been prepared before and could release OH-and Ca2+, were used as the filter medias forBAF. The growth of biofilm and phosphorus removal efficiency of Biological Aerated Filterwith Steel slag-based composite media (SBAF) and Biological Aerated Filter with Blastfurnace slag-based composite media (BBAF) under the condition of dynamic filtration. Thereaction products after backwash were analysed by XRD and SEM-EDS, and the mechanismof phosphate removal of the two BAFs were obtained. The effects of the physical andchemical characteristics of two medias on the removal of COD and NH3-N had beeninvestigated. The influences of organic loading, gas-water ratio and hydraulic loading on theefficiency of two BAFs were studied respectively. And the efficiencies of two BAFs fordomestic wastewater were also studied.The results showed it had been taken15days and22days for SBAF and BBAF byinoculated startup method, and the COD and NH3-N removal rates were above90%. As theresults of OH-released from the medias, the pH were high at the early stage, and it took23days and25days for SBAF and BBAF by natural startup method, during which theefficiencies of remove COD and NH3-N were bad.These two filter medias could release alkalinity and calcium ion, which caused thephosphate removal rate reaching above90%at the start-up stage. The release efficiencydecreased along with the increasing operation time, however, the phosphate removal ratecould be stable at40%and35%, of which were higher than traditional single-stage BAF.The quantity and the active of microorganism on the surface of filter media after the bio-membrane matured were studied, the results of which showed that the number of steelslag metallic oxide media and blast furnace slag metallic oxide media were3.43×109per mg.and1.04×109per mg respectively. The microscopic examination of microorganisms showedthat the biofacies in two BAFs were obviously and the species were diverse. Thecharacteristics of two metallic oxide medias could not inhibit the increase of microorganisms.The results showed that the removal efficiencies of COD, NH3-N and phosphate of twoBAFs were good during steady operation stage, which could be reached at88.36%、95.7%、40.7%and81.68%、89.35%、31.2%respectively, the effluent NO3--N of two BAFs were26.16mg/L and21.84mg/L, and the effluent NO2--N of two BAFs were1.76mg/L and1.62mg/L respectively.The results of the influencing factors about two BAFs showed that the COD and NH3-Nremoval rates of SBAF could be steady along with increasing organic loading of influentwastewater, which increased first and then decreased in BBAF. The COD and NH3-N removalrate of SBAF rose first and then fell with increasing of hydraulic loading, which weredecreased in BBAF. The COD and NH3-N removal rate of two BAFS increased first and thendecreased along with the increase of gas water ratio.In this experimental condition, the phosphate removal of two BAFs was not beeninfluenced by organic loading and hydraulic loading, but influenced significantly by gas waterratio. The phosphate removal rate increased of two BAFs increased from34.32%、27.73%to47.47%and35.21%respectively, when the gas water ratio increasing from1to5.The optimal operating parameters of two BAFs could be obtained, which focused theCOD, NH3-N and phosphate removal of simulated wastewater as the premise, that werehydraulic loading0.15m3/(m2h), gas water ratio3:1and organic loading2.1kgCOD/(m3d). Ithad been investigated for the treatment of actual domestic wastewater with two BAFs underthe above-mentioned conditions, the results of which showed the removal efficiencies of COD,NH3-N of two BAFs were good, but lower than for simulated wastewater. The COD andNH3-N removal efficiency could be improved by improving the Back washing intensity andtime, and the backwash cycle could be increased from5days to7days. It was a feasiblemethod to using these two metallic oxide medias into the treatment of domestic wastewater, and the efficiencies of phosphate removal were higher than traditional filtering media BAF.