This study combines a two-phase biological treatment system of activated sludge/contact aeration process by adding biological-contact filters into the rear sector of the activated sludge aeration tank of the slaughterhouse wastewater treatment plant. This system keeps the advantages of complete mixing of substrates and microorganisms and flexible operation of the activated sludge process, and increased biological phase, less sludge, process stability and good settleability of,sludge of the contact aeration process. This system could avoid the defects of sludge bulking, increased sludge production and difficult operation of the activated sludge process,and system clogging and rigid operation of the contact aeration process. Because suspended microoranisms are flowing into the contact aeration system, which then degrade or suspend within the biological contact filters after being adsorbed by the-fixed biological film, on which partial bio-solids will act as seeding microorganisms. Suspended microorganisms and the dropped biological film will settled in the secondary settling tank, then reflux into the activated sludge aeration tank. The partial dropped biological film will decompose. in the activated sludge aeration tank to achieve the function of decreasing sludge. Large specific gravity and good settling ability of biofilm sludge will provide better effluent quality; It has been proven through a practical experiment at a slaughterhouse wastewater treatment plant in Taiwan, that the activated sludge process effluent COD value of 150-200 md/L and SS value of 80-100 mg/L were decreased to around 40mg/L and 22 mg/L, respectively, after changing its system to the two-phase biological treatment system of activated sludge/contact aeration process.
