Numerous biological, physical and chemical parameters are involved in retention and removal of chemical pollutant and bacteria in wastewater treatment systems. Biofilm presence was often cited for its influence in these mechanisms. Sandy soil is the most used packing material in wastewater treatment study and little information is available for the other soil. The objectives of this study were to compare purification efficiency of packing materials (soil) and to allow a better understanding in purification mechanisms in one-site wastewater treatment. Our work focused on water pollution removal and biofilm development. For this purpose, four experimental reactors were packed with sand and silt suitable for on-site wastewater treatment plant. They were dosed with septic effluent at loads of 5 and 12 cm/j for sand and 2 and 5 cm/j for silt. The purification performances and biofilm development were monitored on 245 for sand filters and 65 days for silt filters. Dissolve oxygen concentration from the treated effluents showed better values for the low loads and for the silt reactors. Also, organic pollutant remove by oxidation (COD and DOC) were better eliminated in the following reactors: Silt (2 cm/j) > Silt (5 cm/j) > Sand (5 cm/j) > Sand (12 cm/j). Adsorption was the mechanism of ammonium removal in silt although nitrification took part in sand. Biofilm development was observed in the first 2.5 cm and 10 cm in the sand reactors loaded at 5 and 12 cm/j respectively.

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