The present investigation raised determine efficiency in removing pollutants from the effluent of a septic tank using a biological filtration system, the system was composed of two units of secondary treatment, a submerged filter and a trickling filter, both with identical characteristics of 1.53 m in height and 0.20 m in diameter. lt was used as packing material, polypropylene rings of % -inch and 2.5 cm in length, placed in both treatment units, forming a height of 1.3 m in the ftlters. For the operation of the submerged filter, and trickling filter system in series, two treatments was performed, with and without artificial injection of air generated by two small air pumps, one for each treatment unit. It was determined that the best removal efficiencies were submerged filter to the 80 days since the start of operation when injected artificial air, concentrations of 16 mg/1 of BOD, 51 ...