Olive washing wastewater treatment by coagulation/flocculation/decantation and UV-A LEDs/Fenton

Olive washing wastewater (OWW) is generated before the olive oil extraction process, in a preliminary step which consists of washing the olives with potable water. The main characteristics of OWW are slightly-acidic pH, dark-brown colour, high turbidity and the presence of recalcitrant phenolic compounds, recognized for their phytotoxicity consequences. Approximately 1 m³ of OWW is generated per processed ton of olives, therefore it is necessary a suitable treatment for a safe disposal in the environment.

The aim of this work was to optimize the experimental conditions of (1) coagulation-flocculation-decantation process and (2) UV-A LEDs/Fenton process. Subsequently was evaluated the use of remaining ferrous ions in (3) CFD/UV-A LEDs/Fenton and (4) UV-A LEDs/Fenton/CFD for OWW treatment.

CFD process, operating at natural pH=4.1, T=25 ᵒC, [Fe²⁺]=3.60 mM, fast mix: 150 rpm/3 min and slow mix: 20 rpm/20 min and 6h of sedimentation, removed 87.9% of turbidity and 49.6% of TSS. UV-A LEDs/Fenton process achieved removals of 80.5% of DOC and 93.7% of COD, at natural pH conditions, T=25 ᵒC, [Fe²⁺]=3.60 mM and [H₂O₂]=116.4 mM, after 120 minutes of reaction. The use of coagulant/flocculant remaining of the CFD process like catalyst in oxidative process reached a total removal of 91.0% of DOC, 97.5% of COD, 95.7% of turbidity and 89.8% of TSS. In conversely way, was achieved a global removal of 80.8% of DOC, 94.1% of COD, 98.4% of turbidity and 91.0% of TSS. As a main conclusion, the combined CFD process followed by UV-A LEDs/Fenton can be selected has a promising approach to OWW treatment.