Treatment efficiency and economic feasibility of biological oxidation, membrane filtration and separation processes, and advanced oxidation for the purification and valorization of olive mill wastewater

Abstract

Olive mill wastewater (OMW) is a major waste stream resulting from numerous operations that occur during the production stages of olive oil. The resulting effluent contains various organic and inorganic contaminants and its environmental impact can be notable. The present work aims at investigating the efficiency of (i) jet-loop reactor with ultrafiltration (UF) membrane system (Jacto.MBR), (ii) solar photo-Fenton oxidation after coagulation/flocculation pre-treatment and (iii) integrated membrane filtration processes (i.e. UF/nanofiltration (NF)) used for the treatment of OMW. According to the results, the efficiency of the biological treatment was high, equal to 90% COD and 80% total phenolic compounds (TPh) removal. A COD removal higher than 94% was achieved by applying the solar photo-Fenton oxidation process as post-treatment of coagulation/flocculation of OMW, while the phenolic fraction was completely eliminated. The combined UF/NF process resulted in very high conductivity and COD removal, up to 90% and 95%, respectively, while TPh were concentrated in the NF concentrate stream (i.e. 93% concentration). Quite important is the fact that the NF concentrate, a valuable and polyphenol rich stream, can be further valorized in various industries (e.g. food, pharmaceutical, etc.). The above treatment processes were found also to be able to reduce the initial OMW phytotoxicity at greenhouse experiments; with the effluent stream of solar photo-Fenton process to be the least phytotoxic compared to the other treated effluents. A SWOT (Strength, Weakness, Opportunities, Threats) analysis was performed, in order to determine both the strengths of each technology, as well as the possible obstacles that need to overcome for achieving the desired levels of treatment. Finally, an economic evaluation of the tested technologies was performed in an effort to measure the applicability and viability of these systems at real scale; highlighting that the cost cannot be regarded as a 'cut off criterion', since the most cost-effective option in not always the optimum one.

Titanium Dioxide Nanoparticle Photocatalysed Degradation of Ibuprofen and Naproxen in Water: Competing Hydroxyl Radical Attack and Oxidative Decarboxylation by Semiconductor Holes

“…Typically AOPs for treatment of organic compounds involve the use of a radiation source in conjunction with inorganic semiconductors such as TiO 2 , in some cases in combination with O 3 , and/or H 2 O 2 , in a process frequently described as heterogeneous photocatalysis. The methodology is approaching economic viability . Both artificial light and sunlight can be used for irradiation, and TiO 2 photocatalysis leads to efficient degradation of pollutants, allowing for complete mineralization in some cases .…”

Chemical Coagulation/Flocculation Processes for Removal of Phenolic Compounds from Olive Mill Wastewater: A Comprehensive Review

“…AOPs have been extensively studied for the OMW treatment through ozonation, photo-Fenton oxidation, TiO 2 photocatalysis, electrochemical oxidation and wet air oxidation. Their efficiency was found to be significatif (Gernjak et al, 2004;Canizares et al, 2007;2009;Chatzisymeon et al, 2009;Mert et al, 2010;Belaid et al, 2013;Michael et al, 2014;Ioannou-Ttofa et al, 2017;Davididou et al, 2018). Although, AOPs manage a great COD reduction, but their operating costs are considerably high.…”

“…Membrane processes, such as MF, UF, NF and RO, have been proposed to obtain effluent streams from OMW of acceptable quality for safe discharge in the environment, tree or land irrigation, or even for recycling and reuse in the olive mill facilities (Cassano et al, 2011;Ochando-Pulido et al, 2014;Zagklis et al, 2015;Sanches et al, 2016;Kontos et al, 2016;2018;Ioannou-Ttofa et al, 2017). Most of these studies indicated that membranes processes exhibit high selectivity values required to achieve high water quality standards.…”

“…They are more cost-effective than other conventional processes, require less area and can replace several unit treatment processes by a single one. However, the implementation of membrane technologies in OMW treatment suffer from various drawbacks, such as the membrane fouling, the energy cost and the membrane replacement (Miguel and Pulido, 2016;Ioannou-Ttofa et al, 2017). In addition, the concentrate generated contains high levels of refractory organic pollutants and inorganic salts which needs further treatment before its disposal in the environment, Advanced Oxidation Processes (AOPs) are based on the creation of very reactive species, such as hydroxyl radicals (HO .…”

Continuous flow adsorption of phenolic compounds from olive mill wastewater with resin XAD16N: life cycle assessment, cost–benefit analysis and process optimization

“…There are five main novel elements of this study: The LCA of the PC adsorption process: this aspect has been included so far in a very limited number of studies on PC recovery from different matrixes by solvent extraction and subcritical water extraction, but never on PC recovery by adsorption. The CBA of the PC adsorption process: a few studies have reported the economic evaluation of processes of PC recovery by reverse osmosis, combined ultrafiltration/nanofiltration, supercritical fluid extraction and thermal treatment combined to centrifugation, but none have done so for adsorption. The development of an LCA and CBA of the PC recovery process based on the design of a full‐scale plant: this includes all the equipment required to produce a PC‐rich product, in addition to the adsorption/desorption column (OMW filtration unit, rotary dryer with gas boiler for ethanol evaporation, condenser for ethanol recovery, cooling tower, tanks and pumps); previous studies on the process LCA and CBA did not include an evaluation of the cost and environmental impact associated with the purchase, operation and decommissioning of the auxilliary equipment required to produce a marketable antioxidant product. The model‐based study of the effect of fluid velocity on the performances of the PC adsorption process. The assessment of the process performances during consecutive adsorption/desorption cycles: this aspect has been partially investigated for a continuous flow process only in one previous study which evaluated – over five consecutive cycles – the composition of the desorbed product, but not the adsorption yield or the resin operating efficiency. …”