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Olive oil mill wastewater (OMW) is generally recognized as an environmentally troublesome by-product of the olive oil industry as its disposal without any treatment is known to cause serious environmental problems. However, this effluent has a high fertilizing power and constitutes, with urban wastewater, an important low-cost source. Biological treatment of OMW, with a process combining an aerobic reactor, 'Jet-Loop', and waste stabilization ponds, was investigated for possible agricultural reuse. The focus of the present study was to evaluate the contribution and the complementarity of the two systems in the total OMW treatment. Bio-treatment was performed using a 100-litre Jet-Loop reactor working volume achieving a chemical oxygen demand (COD) and phenolic compounds maximum removal rate of 72% and 68%, respectively, at a hydraulic retention time of 10 days. Co-treatment of OMW and domestic wastewater in waste stabilization ponds, with a hydraulic retention time of 22 days, reached a global removal rate of 66% for COD while no trace of phenolic compounds was detected on this level during the entire treatment period. Dynamics of faecal coliforms in stabilization ponds showed a total removal rate of 99.9% (3 logarithmic units (Log.U)). Preliminary results of agronomic tests on the ray-grass have evaluated the fertilizing effect of the final effluent resulting from the co-treatment.

Olive Oil Waste Water (OOWW) is acidic water known for its antibacterial and phytotoxic effects. In Morocco, these effluents are generally drained into the surrounding environment without any treatment or are collected and retained in large evaporation basins, which can constitute a source of potential pollution of groundwater. The analysis of water from 14 wells, in an agricultural zone, where there are four storage basins of OOWW coming from various types of oil mills, showed that their physicochemical and biological quality is largely influenced by the presence of these basins. Indeed, high values of COD (400 mg O2 L(-1)), polyphenols (180 mg l(-1)) and electrical conductivity (1.89 mS cm-') were recorded in P5 water. This well is located only 5 m from a storage basin of OOWW coming from the H4 oil mill which rejects OOWW charged with organic matter (more than 290 g of O2 L(-1) of COD, on average). However, the settlement of a basin, dug close to a modern oil mill (H3), which produces large OOWW volumes but is loaded with low organic pollutant concentration (100 g of O2L(-1) of COD), reduced notably the effect of the OOWW infiltration on groundwater. This resulted in the improvement of the groundwater physicochemical quality near this basin (P7 and P8); the organic matter contents expressed by COD vary from 26.7 mg l(-1) to 30 mg l(-1) and the polyphenol contents are on average between 41 mg l(-1) and 47.6 mg l(-1). The analysis of the total well water fauna showed a great taxonomic richness with variations in time and space. The biodiversity decreases in groundwater polluted by the oil mill waste and the underground fauna disappears completely if the degree of contamination of groundwater is high.