**2. Materials and methods**

by Portugal, France, Cyprus, Croatia, Turkey, Syria, and Tunisia. New producers are Argen‐

Olives are processed through two methods: pressing (discontinuous process) and centrifuging (continuous process, two/three phase centrifugation). The main inconvenience of these methods is the production of a polluting by-product that is a dark effluent known as olive mill

The environmental impact of olive oil production is strong due to the use of large quantities of

are by-products generally considered undesirable but inevitable for every olive processing.

As defined in reference [3], OMW is "a stable emulsion constituted by vegetation waters of the olives, water from the processing, olive pulp and oil." It is characterized by a particular color (intensive violet-dark brown up to black color), odor (strong specific olive oil smell), high degree of organic pollution (expressed as biological and chemical oxygen demand (BOD and COD) values), acidic pH, high electrical conductivity, high content of polyphenols, high buffer

OMWs are generally composed of water (83%–96%) and organic fraction (3.5%–15%) com‐ posed of 1%–8% carbohydrates, 0.5%–2.4% nitrogen compounds, 0.5%–1.5% organic acids, 0.02%–1% of fatty acids such as propionic, butyric, etc., and 1%–1.5% of phenolic compounds consisting of a hydroxyl group (-OH) bound directly to an aromatic hydrocarbon group and

Concerning phenols, they comprise low molecular weight compounds and polyphenols. Low molecular weight compounds are represented by caffeic, cinnamic, 2,6-dihydroxybenzoic, *p*hydroxybenzoic, syringic, 3,4,5-trimethoxybenzoic, vanillic, and veratric acids; they have phytotoxic effects and antibacterial activity. Polymeric phenols (lignins, tannins, etc.) cause the typical brownish-black color of OMW and are the most recalcitrant fraction of this effluent.

The quantitative and qualitative composition of OMWs are variable due to climatic conditions, variety, ripeness of olives, and extraction processes; generally, they are produced in high

As OMWs are rich in nutrients they could be used to remediate arid or semi-arid regions but their phytotoxicy affect plant growth [5]. OMWs have the highest polluting rate within the food industry due to the fact that they are recalcitrant to traditional biodegradative methods. The reduction of COD and BOD values represent an important goal for many industries but the high content in phenols complicate waste management; they exert an antimicrobial activity

For these reasons phenols are considered as undesirable compounds; thus, physical, chemical,

Waste remediation has been traditionally performed through some expensive methods (incineration, pyrolysis, landfill, etc.). In recent years, the increasing trends towards green economy and friendly approaches for the environment are the background to design alterna‐

quantities in a short time, thus their disposal represents an important problem.

towards wastewater microflora thus biodegradation is slowed [6].

or biological treatments are used to reduce their pollutant load.

–1.5 m3

of OMWs [1]. They

water and the production of OMW: 1,000 kg of olives produce 0.5 m3

tina, Australia, and South Africa.

capacity, and high content of solid matter.

wastewater (OMW) [2].

86 Wastewater Treatment Engineering

pectins [4].
