Contaminant removal performace of three different contact mediums (broken stones, plastic submerged rings, and kureharon lock) in a contact oxidation reactor of a soil absorption system was investigated in the laboratory. The objective of the experiments was to determine a practical contact medium for the reactor from the standpoint of technical and economical efficiency. Replacement of commercial microbial additives incorporating on-site compost in the soil absorption layer over the upper surface of the oxidation reactor was also evaluated as an alternative in an effort to reduce the initial investment. The results of experiment shod the BOD_5, CODcr, and SS removal efficiency of kureharon lock medium were slighly higher by 2-7% than submerged rings or broken stones, with a lower organic loading rate of 0.20 BOD_5/㎥/day. However, with a higher organic loading rate of 0.80 BOD_5/㎥/day, the lock medium performed much better by removing 15-20% more than the other two media. Nutrient (T-N, T-P) removal efficiency followed a similar pattern. With all ranges of organic loading rates, the lock medium showed a higher performance in nutrient removal by 15-25%. However, the plastic submerged ring medium did not show any improvement over broken stone medium. This result may be related to the specific area of the mediums, which provides space for microbes to live and mutiply. The kureharon lock medium is a more technically efficient contact medium for removal of organic matter and nutrient, but application volume of the medium must be optimized because it is expensive. The on-site compost did not reveal any deficiency over the commercial microbial additives in physical and biological properties of the soil absorption system. The on-site compost was higher in water holding capacity, but lows in FAS(Free Air Space) than commercial additives and microbial density of the two composts was more or less the same. The onsite compost can be a good alternative to replace the commercial products, reducing initial investment without reducing effectiveness.