COD removal in biological aerated filter system

This paper presents the study on the COD removal efficiency of the domestic wastewater by the up-flow two-stage Biological Aerated Filter (BAF). Two kinds of materials including ceramic and activated carbon were used to fill the first and the second filter, respectively. The performance of COD removal in the different periods was compared when evaluated in a series of laboratory tests designed to change filter velocity and aeration. The reactor set up successfully at the velocity range from 1 m/h to 2 m/h by natural forming bio-film, and maintains the most stabile removal efficiency at the velocity of 3 m/h similar to 5 m/h. At the same time, some pronounced phenomena were reflected during the tests. The total average removal ratio of COD approaches 90% on condition of the 3 m/h velocity and 25 L/h aeration. With the increasing of velocity and aeration, 4m/h and 37.5 L/h, the COD removal ratio still kept up to 88.2%. When the velocity equaled to the constant 5 m/h and the aeration rose from 37.5 L/h to 50 L/h, the ratio declined to some extents, because the disturbance caused by the powerful up-flow water and air current enlarged voids in the filter layer. The air-liquid back-washing was conducted in order to remove the older excess biomass and the rejected suspension.