Multistage treatment for olive mill wastewater: Assessing legal compliance and operational costs

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 Al-2(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 (O-3). 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 O-3 process (inlet concentration = 100 mg O-3 Ndm(-3), gas flow = 0.2 Ndm(3) 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 euro m(-3). Regarding the most effective AOPs, ozonation presented an estimated cost 2.3-fold higher than PF-UVA (11.9 euro m(-3) vs. 5.2 euro m(-3)).

Automated summary

A treatment train for the remediation of raw olive mill wastewater was investigated, and a system consisting of pre-treatment, coagulation, biological oxidation, and advanced oxidation process (AOP) was proposed. The coagulation and biological oxidation stages achieved high removal efficiencies of various pollutants, while different AOPs had varying degrees of effectiveness. The operational costs for the different stages varied, with ozonation being the most expensive.