Treatment of olive mill and municipal wastewater mixture by pilot scale vertical flow constructed wetland

The aim of the present study is to examine the feasibility of a pilot scale constructed wetland (PS-VFCW) in which pozzolan is adopted as new filling media to enhance the treatment efficiency of a mixture of olive mill wastewater (OMWW) and municipal wastewater (MWW). Special attention was devoted to the removal of specific toxic phenolic compounds. The PS-VFCW consisted on a polyvinyl chloride tank (height: 0.60 m, diameter: 0.56 m, and surface area: 0.24 m(2)). The pilot plant was planted with Phragmites australis and filled from the bottom with 10 cm of gravel, 10 cm of pozzolan, and 30 cm of sand. The applied hydraulic loading rate (HLR) was 60 L/m(2)/d with a mean influent concentration of 6,100; 131; 9.45; 10.19; 232; 2.04; and 12.40 mg/L for chemical oxygen demand (COD), polyphenols, orthophosphates (PO43-), total phosphorus (P), sulfate (SO42-), nitrite (NO2-), and ammonium (NH4+), respectively. The PS-VFCW was monitored for a period of 1 y. Obtained results show that the PS-VFCW achieved high removal rates: 91%, 89%, 94%, 94%, 58%, 92%, and 95%, respectively for COD, polyphenols, PO43-, P, SO42-, NO2-, and NH4+. High pressure liquid chromatography (HPLC) analysis of phenolic fractions in studied effluents highlights the removal of a variety of these compounds, especially toxic one's such as tyrosol and hydroxytyrosol after treatment by the PS-VFCW. Moreover, analysis on the CW filling medium demonstrates the absence of phenolic compounds which is probably due to their biodegradation by microorganisms or adsorption by pozzolan.