Evolution of several soil properties following amendment with olive mill wastewater

Occurrences of olive mill wastewater (OMW) amendment on several chemical and biochemical properties of soil were investigated. Compared to the control, soils amended with untreated and treated OMW (by an integrated process based on aerobic fungal pre-treatment using Phanerochaete chrysosporium DSMZ 6909 followed by anaerobic treatment) showed high levels of organic and mineral matters. Soil amended with untreated OMW presented low levels of total and inorganic nitrogen (0.38 and 0.08 mg g^?1 dry soil). Treated OMW contained little content of pollutants (COD = 4 g l^?1; phenolic compounds = 0.6 g l^?1); so, organic matter brought by these residues was rapidly mineralized in the soil. The number of heterotrophic bacteria was increased (from 54 × 10⁵ CFU g^?1 dry soil in control soil to 123 × 10⁵ CFU g^?1 dry soil) in response to the OMW amendment, mainly after C/N ratio correction. Untreated OMW application improved the soil carbon content (2.18 times higher), while the specific respiration remained very low. However, the treated OMW application positively affected the soil-specific respiration that increased from 6.1 in control soil to 9.75 in soil amended with treated OMW. This phenomenon was accompanied by an enhancement of nitrifiers number, urease and ammonium oxidases activities.