Infiltration–percolation is an extensive treatment technique aimed at eliminating organic matter, oxidizing nitrogen, and removing pathogens. The main purpose of this work is to evaluate the impact of fractionation of hydraulic load on oxidation performances of unsaturated sand filters. Experimental results showed that oxidation of organic matter and ammonium nitrogen has mainly occurred in the upper layers of the filter bed. They also showed that treatment efficiency increased with the increase of the thickness of the filtering mass and the fractionation of applied hydraulic load. The experiments pointed out the influence of the fractionation of daily load on oxidation capacity of the intermittent sand filter. Results showed that increasing the fractionation improves the purification capacity of the treatment process. The simulations showed that biomass growth is very sensitive to the fractionation of hydraulic load, and that the increase of the number of feeding–drainage cycles per day leads to accumulate purifying biomass in the upper layers of unsaturated filters.