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This study aimed to assess the efficiency of multilayer biofiltration systems for the removal of organic matter and nutrients from raw, diluted, and pretreated olive mill wastewater (OMW) by coagulation -flocculation using lime. The experimental setup consisted of four PVC columns. The first column, serving as the control column, was filled with sand only and fed with raw OMW. The remaining columns were packed with multilayer biofilters composed of 70 % sand, 20 % oyster shells, and 10 % sawdust. Each of these columns was fed with raw, diluted with domestic wastewater (1:1), and pretreated OMW. Percolation through the columns resulted in an increase in both electrical conductivity and pH values. A high removal of total COD was observed in the column fed with diluted OMW (62.75 %). Regarding dissolved COD, high removal was achieved in the control column (67.84 %), as well as in the columns fed with raw OMW (51.34 %), diluted OMW (78.61 %), and pretreated OMW (51.08 %). Phenolic compound removal also reached high percentages in the column fed with diluted OMW (64.82 %). Concerning nutrient removal efficiency, substantial removal of orthophosphate (PO₄ 3− ), total phosphorus (TP), and ammonium (NH₄ + ) was achieved in the control column (58.83 % – 62.28 % – 35.12 %), the raw OMW column (47.97 % – 50.96 % – 40.07 %), and the diluted OMW column (59.44 % – 59.74 % – 49.67 %), respectively. Based on these findings, the use of sand and sand mixed with substrates, combined with diluted OMW, appears to be an effective approach for the removal of total COD (62.75 %), dissolved COD (78.61 %), phenolic compounds (64.82 %), orthophosphate (PO₄ 3− ) (59.44 %), total phosphorus (TP) (59.74 %) and ammonium (NH₄ + ) (49.67 %) from OMW. Based on this preliminary study, the treated OMW may be considered for agricultural reuse, particularly in restricted irrigation applications, as long as the residual salinity and organic load do not pose risks to soil quality or plant growth.
Asdiou et al. (Thu,) studied this question.