In this study, a novel strategy for olive mill wastewater (OMW) treatment, which combines an
evaporation–condensation step followed by the biological treatment of the condensate, was evaluated.
Different solutions were evaluated as biological step, through a experimental tests, by operating for three
weeks: two bench scale sequencing batch reactor (SBR), with and without media for attached growth,
and two pilot scale constructed wetlands, a vertical (VF) and a horizontal (HF) submerged
flow beds.
When treating an influent OMW with a COD concentration in the range from 130 to 150 g L1, the
evaporation/condensation process allowed to achieve up to 98.7% of COD removal (2.4 g COD L1 in
average in the condensate); moreover, the condensate showed a large biodegradable fraction, allowing
the further treatment of the residual COD by simple biological reactors like SBRs or constructed wetlands
(CWs). The CWs, either in HF or VF configuration, showed more stable and barely higher performances in
comparison with the SBR, especially during the
first week of operation and allowed to obtain an effluent
with a pH close to neutrality without alkalinity dosing. The overall COD removal was about 99.8% and less
than two weeks were needed for the start-up of the biological system, which is of pivotal importance
given the olive mill process cycle. The evaporation process also generated a concentrate containing a high
concentration of valuable chemicals, including polyphenols.