Comparison of Polypropylene and Zeolite Medium Combined in Biological Aerated Filter Treating Domestic Sewage

Treatment efficiency and microorganisms´ property of polypropylene and zeolite medium coupled in biological aerated filter(BAF) were investigated in this paper. The reactors were operated in parallel with upflow mode using domestic sewage as influent up to BOD5 volumetric loading of 3 kg BOD₅·m^-3d^-1, NH₃-N surface loading of 0.5 g NH₃-N·m^-2d^-1, and air/liquid ratio of 10:1 in room temperature. The results suggested that the differences of COD removal were not obvious for these two carriers, and the removal efficiency was up to 85%. In addition, the nitrogen removal ability was limited for both, the removal efficiency of NH₃-N and TN by polypropylene BAF was 77% and 36% respectively. On the contrary, nitrification was improved by 11% contributing to ion exchange capacity of zeolite, and the total nitrogen removal capacity was equal to 55% for the inner anoxic environment. The results of biomass and biofilm activity change were similar in these two mediums. Biomass tended to decrease gradually along water flow, and that the biofilm activity change appeared obvious characteristics of reversed ¿V¿ shape. The activity enrichment was obtained at the point of organic famine transferring to feast regime. Overall, zeolite was superior to polypropylene in biological aerated filter process, and the special structure was beneficial to nitrogen degradation.