Treatment of secondary wastewater effluents by infiltration percolation

Infiltration percolation is a rustic and extensive purifying technique which is capable of completely oxidizing and decontaminating wastewater. Secondary effluents, intermittently applied over 100 m2 infiltration basin, percolated through unsaturated coarse sand. Each application sequence delivered a volume of 0.27 m3/m2 of sand bed. Analyses of the filtered water sampled at 50, 100 and 150 cm bed depths showed that oxidation performance of the pilot basin was highly dependent on both the bed depth and the water temperatures. Results showed that high water temperature improves oxidation efficiency. In summer season, more than 90% COD was removed and more than 94% N–NH4 oxidized. Water quality analyses demonstrated that oxidation activity was mainly located in upper sand layers. Disappointing removal of total coliforms, faecal coliforms and streptococci was attributed to high pore water velocities due to infiltration heterogeneity and the high water height applied during each feeding sequence. It was demonstrated that the microorganism removal increases with the depth of filtering medium and the water temperature.