Research On The Start-up And Treatment Performance Of Biological Aerated Filters With Different Carriers

Two biological aerated filters with ceramsite and porcelain carriers were used to treat domestic wastewater in this experiment. A contrastive study was made on the start-up, film formation and major factors which influenced the performance of the two BAFs. The factors included media height, air to liquid ratio, hydraulic retention time, influent organic concentration and so on. The main conclusions were drawed as below:1.The time needed for the start-up and film formation of the two BAFs were different, for BAF with ceramsite carrier, 10 days were needed, but for BAF with porcelain carrier, 30 days were needed.2.The removal of CODcr did not keep in pace with that of NH₄⁺-N in the process of film formation. In this experiment, the CODcr removal and nitrification efficiency of BAF with ceramsite carrier were higher than BAF with porcelain carrier, and less time was needed to get a stable CODcr removal.3.The result of optical bio-microscope observation showed that ecosystem with many kinds of different microbes and distinct biological phase distribution was formed in the two BAFs.4.When temperature was 24.0～32.9℃, CODcr concentration in influent was 90.6～419.0mg/L, NH₄⁺-N concentration was 7.85～36.51mg/L, the gas to liquid ratio was 3:1 and HRT was 12h, in both BAFs, remarkable SS removal was achieved in the media height of 40cm,the optimum media height for the removal of COD and NH₄⁺-N were 60cm and 60～100cm respectively. TP removal was mainly achieved in the media height of 40～80cm and 40cm in BAF with ceramsite and porcelain carriers respectively. The biological phosphorus removal of the two BAFs were not good. In whole, BAF with ceramsite carrier had better removal of SS, CODcr and NH₄⁺-N than BAF with porcelain carrier.5.When temperature was 24.0～32.9℃, HRT was 12h, CODcr concentration in influent was about 300mg/L, the influence of gas to liquid ratio on the performance of the two BAFs was studied in the experiment. The results showed that, when gas to liquid ratio were 1:1,3:1 and 5:1 respectively, increase of gas to liquid ratio caused better removal of CODcr and NH₄⁺-N in the two BAFs. In order to get a good removal of NH₄⁺-N, the gas to liquid ratio should be about 1:1 for BAF with ceramsite carrier and 3:1 for BAF with porcelain carrier.The effect of simultaneous nitrification-denitrification in the two BAFs was not good, increase of gas to liquid ratio caused worse removal of TN. We should adopt pre-denitrification BAF process or two-stage BAF process to get better removal of TN.6.When temperature was 11.5～32.9℃,gas to liquid ratio was 3:1,CODcr concentration in influent was 90.6～419.0mg/L,NH₄⁺-N concentration was 7.85～47.51mg/L, SS concentration was 80～270mg/L, HRT was 12h,10h,8h,5h and 3h respectively, the relation between CODcr removal rate and hydraulic retention time was not linear, there was a optimum HRT, which was 10h for the two BAFs in this experiment. Reduction of HRT caused reduction of NH₄⁺-N and SS removal rate in the two BAFs, variation of SS removal rate was not obvious. In whole, the removal performance of pollutants of BAF with ceramsite carrier was better than BAF with porcelain carrier.7.When temperature was 11.5～32.9℃,HRT was 12h, gas to liquid ratio was 3:1, we adjusted the influent organic concentration to about 100mg/L,200mg/L,300mg/L and 400mg/L respectively through dilution or adding dextrose to study the influence of influent organic concentration on the performance to the two BAFs. The results showed that, increase of influent organic concentration caused increase of CODcr removal, but almost no variation of NH₄⁺-N removal in the two BAFs, which indicated that both BAFs had strong resistance to impact of organic load and stable NH₄⁺-N removal.8.With consideration of the influencing factors,high effective and low-consumptive requirements in project applications,optimal operational parameters for two BAFs were:HRT was 12h,air to liquid ratio was 3:1,media height was 1m.9.Comparison of project cost was made between the two carriers, price of ceramsite was higher,but when referring to the cost of running and maintenance,higher interspace rate of ceramsite carrier caused difficult backwashing.Spherical porcelain carrier was easy to backwash and needed less amount of liquid and air,which caused less cost in running and maintenance.