A treatment train for the remediation of a raw olive mill wastewater (OMW) was investigated, aiming to comply
with the emission limit values (ELVs) for direct discharge into water bodies. The following stages were proposed:
(i) pre-treatment (filtration and sedimentation), (ii) coagulation, (iii) biological oxidation, and (iv) advanced
oxidation process (AOP). Under the best-operating conditions for coagulation (0.8 g L- 1 of Al2(SO4)3, pH = 4.5),
high removal of total suspended solids (TSS) (97%), turbidity (98%), and phenols (57%) was achieved, along
with a decrease in the inhibition of the biological activity. A subsequent biological oxidation stage provided a
high removal of organic matter (chemical oxygen demand (COD) removal of 73%). For the third stage, three
AOPs were applied and compared – photo-Fenton with UVA radiation (PF-UVA), anodic oxidation (AO), and
ozonation (O3). After 3 h of treatment, the PF-UVA process (pH = 2.8, [H2O2] = 400–500 mg L- 1, [Total dissolved
iron]0 = 100 mg L- 1) allowed to meet the ELV for COD, but the other parameters exceeded the threshold,
while O3 process (inlet concentration = 100 mg O3 Ndm- 3, gas flow = 0.2 Ndm3 min- 1) allowed to comply with
phenols, TSS, and sulfate limits. The AO process (current density up to 200 mA cm- 2) was the least efficient AOP
for all studied parameters. The operational costs for the coagulation and biological oxidation stages were estimated
at 1.20 € m- 3. Regarding the most effective AOPs, ozonation presented an estimated cost 2.3-fold higher
than PF-UVA (11.9 € m- 3 vs. 5.2 € m- 3).
This work was financially supported by (i) LA/P/0045/2020 (ALiCE), UIDB/50020/2020 and UIDP/50020/2020 (LSRE-LCM), funded by national funds through FCT/MCTES (PIDDAC), and (ii) Project NORTE-01-0247-FEDER-072124, Bagaço+Valor - Tecnologia Limpa para a Valorização dos Subprodutos do Bagaço na Indústria Extratora de Azeite, funded by the European Regional Development Fund (ERDF). Srikanth Vuppala acknowledges the Joint Research Projects for the International Mobility of the XXXI and XXXII cycle PhD students for the project: CHEMBIOCAT, La Sapienza University of Rome. Larissa O. Paulista and Daniela F.S. Morais acknowledge their Ph.D. scholarships supported by FCT (SFRH/BD/137639/2018 and SFRH/BD/146476/2019, respectively).
Francisca C. Moreira and Vítor J.P. Vilar acknowledge the FCT Individual Call to Scientific Employment Stimulus 2017 (CEECIND/02196/2017 and CEECIND/01317/2017, respectively).
