An olive mill's existing evaporation pond was separated into five cells and
transformed into a free water surface constructed wetland. The constructed
wetland was used as a post-treatment stage for olive mill wastewater (OMW).
Wastewater was previously treated by an aerobic trickling filter. The
influent concentrations in the constructed wetland were 27400 mg.L-1, 4800
mg.L-1, 105 mg.L-1 and 770 mg.L-1 for COD, phenols, ortho-phosphate and TKN,
respectively. Despite the rather high influent concentrations, the
performance of the constructed wetland was very good since after the 60-day
start-up operation period it achieved removal rates of about 94%, 95%, 95%
and 98% for COD, phenols, ortho-phosphate and TKN, respectively. The major
pollutant removal processes can be attributed to both biological processes
occurring in the wetland and photo-oxidation. Laboratory-scale experiments
with OMW from fifth cell of the wetland revealed that the net contribution of
photo-oxidation after 112 hours of simulated solar radiation at 765 W/m2
(i.e. about 38 days of sunlight irradiation) was 18% and 31% removal for COD
and phenols, respectively. In the constructed wetland, the total removal
reached 81% and 86% for COD and phenols, respectively, for the same time
period (38 days).