Treatment of modern olive mill effluent by infiltration-percolation on a sand filter
Industrial olive oil production is of fundamental economic importance for many countries from the Mediterranean Sea. However, during olive oil production, large amounts of polluted waters, known as olive mill wastewaters (OMW), are generated. Discharge of this effluent into receiving waters without treatment leads to serious environmental problems in these countries. Many studies have been undertaken to find efficient treatment systems and several techniques have been tested, but there have been few studies investigating sand filters for this type of effluent. The purpose of this work was to test the suitability of sand filters to treat olive mill wastewater, specifically by a 50% dilution of OMW with domestic wastewater. Results show that the initial OMW had an acidic pH (4.93) due to the presence of substances such as phenolic acids and fatty acids. The electrical conductivity was very low (9.6 mS•cm‐1) compared to that reported from urban effluents in Marrakech (Morocco). This OMW contained high amounts of phenolic substances (1.42 g•L‐1), total Chemical Oxygen Demand (28 g COD•L‐1) and dissolved Chemical Oxygen Demand (18 g COD•L‐1). During the first week, the treatment of the raw OMW with a sand filter allowed an increase of pH (from 4.93 to 7) and electrical conductivity (from 10.2 to 15.4 mS•cm‐1), and a reduction of the following parameters: total COD (36%), dissolved COD (33%), phenol contents (53%), total Kjeldahl nitrogen NTK (67%) and ammonium (75%). In a sand column, percolation of diluted OMW with domestic wastewater allowed an increase of pH (8.03) and significantly improved the removal efficiency of total COD (76%), dissolved COD (92%), phenols (90%), NTK (50%) and ammonium (87%).