Treatment of olive mill wastewaters using infiltration/percolation system: effect on microbial communities in the soil filter

Infiltration/percolation is a low-technology process that has low energy and maintenance requirements and could be used to completely oxidize and decontaminate primary or secondary wastewaters. The objective of this work is to determine the performance of a soil filter implemented in Ait Ourir (Marrakech region - Morocco) for the treatment of olive mill wastewater (OMW). The experimental pilot consists of three basins of 12 m x 8 m each (length x width) built using reinforced concrete. A storage basin followed by a soil filter filled with 60 cm height of soil and 90 cm of gravel at the bottom. The 3rd basin was used to collect the treated OMW. The alimentation of the filter was continuous from the storage basin starting on November 15th until the end of January. The OMW was very acidic with a pH of 4.3, an electrical conductivity of 19.33 mS/cm, a total phenolic content of 2.78 g/L, and a total organic carbon of 3.12 g/L. The percolation of the OMW through the soil filter with gravel causes a reduction of 68% of suspended solids, 52% of fat contents, 69% of the total organic carbon, and 55% of the phenolic content. An analysis of microbial communities of soil filter was undertaken in comparison to control soil. The obtained results show the potentiality of an infiltration/percolation system (soil filter) to treat OMW before its use as fertilizer. Further investigations are needed to assess the toxicity of the treated effluents and their suitability for irrigation since some of their physico-chemical characteristics did not meet the Moroccan standards for wastewater reuse in irrigation.