Investigation of two ultrafiltration membranes for treatment of olive oil mill wastewater

In this study, a promising treatment method is given for the olive oil mill wastewater (OMWW). Although the same steps of this method have been used in different studies before, flow scheme is novel. The membrane filtration of pretreated OMWW was investigated by using two ultrafiltration membranes in this study. Pretreatment steps were pH adjustment (pH = 2) and cartridge filter filtration, and pH adjustment (pH = 6) and cartridge filter filtration. Each step of cartridge filter filtration was batch process and effluent from the filter was recycled back to OMWW tank. Pretreated OMWW was sent to feed vessel of experimental set-up. Recovery of olive oil in the OMWW was realized collecting it from the top of pretreated OMWW. Ultrafiltration membranes used were JW and MW membranes supplied by Osmonics. The effects of main operating parameters (transmembrane pressure, feed flow rate, pH and membrane type) on the permeate flux and membrane fouling were examined. The effectiveness of the different membranes and operating conditions was evaluated using retention coefficients calculated from COD and TOC of experimental studies. The highest permeate flux (25.9 l/m² h) was obtained using MW membrane under operational conditions of Qf = 200 l/h flow rate and TMP = 4 bar, while the highest removals were obtained at Qf = 100 l/h flow rate and TMP = 1 bar. COD, TOC, SS, oil and grease concentrations of MW membrane effluent were 6400 mg/l, 2592 mg/l, 320 mg/l, and 270 mg/l, respectively.     

Hydrothermal gasification of olive mill wastewater as a biomass source in supercritical water

In this study, the hydrothermal gasification of biomass in supercritical water is investigated. The work is of peculiar value since a real biomass, olive mill wastewater (OMW), is used instead of model biomass compounds. OMW is a by-product obtained during olive oil production, which has a complex nature characterized by a high content of organic compounds and polyphenols. The high content of organics makes OMW a desirable biomass candidate as an energy source. The hydrothermal gasification experiments for OMW were conducted with five different reaction temperatures (400, 450, 500, 550 and 600 °C) and five different reaction times (30, 60, 90, 120 and 150 s), under a pressure of 25 MPa. The gaseous products are mainly composed of hydrogen, carbon dioxide, carbon monoxide and C₁-C₄ hydrocarbons, such as methane, ethane, propane and propylene. Maximum amount of the gas product obtained is 7.71 mL per mL OMW at a reaction temperature of 550 °C, with a reaction time of 30 s. The gas product composition is 9.23% for hydrogen, 34.84% for methane, 4.04% for ethane, 0.84% for propane, 0.83% for propylene, 49.34% for carbon dioxide, and 0.88% for minor components such as n-butane, i-butane, 1-butene, i-butene, t-2-butene, 1,3-butadiene and nitrogen at this reaction conditions.     

Removal of organic load and phenolic compounds from olive mill wastewater by Fenton oxidation with zero-valent iron

Pre-treatment of olive mill wastewater (OMW) by Fenton Oxidation with zero-valent iron and hydrogen peroxide was investigated to improve phenolic compounds degradation and the chemical oxygen demand (COD) removal. Experimental procedure is performed with diluted OMW with COD 19 g/L and pH 5.2. The application of zero-valent Fe/H₂O₂ procedure allows high removal efficiency of pollutants from OMW. The optimal experimental conditions were found to be continuous presence of iron metal, acidic pH (2–4) and 1 M hydrogen peroxide solution. The experimental results show that the removal of 1 g of COD need 0.06 M of H₂O₂. At pH 1, the maximum COD removal (78%) is achieved after 1 h. Therefore, with a pH value within 2 and 4 the maximum COD removal reached 92%. Phenolic compounds are identified in treated and untreated OMW by gas chromatography coupled to mass spectrometry (GC–MS). The result shows a total degradation of phenolic compounds and an increasing biodegradability of treated OMW.     

Catalytic wet air oxidation of olive oil mill effluents: 4. Treatment and detoxification of real effluents

Olive oil mill wastewater (OMW) generated by the olive oil extraction industry constitutes a major pollutant, posing severe environmental threats. It contains a high organic load and phytotoxic and antibacterial phenolic compounds which resist biological degradation. Platinum and ruthenium supported titania or zirconia were studied in the catalytic wet air oxidation (CWAO) of OMWs in a batch reactor and in a continuous trickle-bed reactor. CWAO experiments at 190 °C and 70 bar total air pressure confirmed the effective elimination of the TOC (total organic carbon) and of the phenolic content of actual diluted OMW. Simultaneously, toxicity towards Vibrio fischeri was reduced and a decrease in phytotoxicity occurred. The ruthenium catalysts were found stable over a long period of operation in a trickle-bed reactor.The biodegradability of the oxidized waste has been enhanced and this study also examined the feasibility of coupling CWAO and an anaerobic digestion treatment. The pretreatment of the OMW in the presence of a ruthenium catalyst reduced considerably the total phenolic contents of the wastewater, and produced an effluent suitable to be treated by anaerobic treatment with increased biomethane production compared to the untreated effluent.     

Contaminants and salinity removal of olive mill wastewater using zeolite nanoparticles

Successive columns of gravel, fine sand, and mixture of acidified cotton and zeolite clinoptilolite nanoparticles (ZNP) were found efficient in olive mill waste water (OMW) treatment and desalination. The treatment decreased OMW’s salinity from 10.9 to 1.6 dSm^?1 due to K⁺ removal. Furthermore, most total phenol contents were removed. The adsorption of K⁺ (aqueous solution) onto normal zeolite particles (NSP) and ZNP indicated that the pseudo-second order kinetic model is best model for K⁺ adsorption. Langmuir model was best fit model for K⁺ adsorption equilibrium. K⁺ maximum adsorption capacities were 7.2 and 16.5 mgg^?1 for NSP and ZNP, respectively.     

Threshold flux measurement of an ultrafiltration membrane module in the treatment of two-phase olive mill wastewater

The critical and threshold flux theories represent an important advance in membrane knowledge. Comprehension of the flux behavior of ultrafiltration (UF) membranes is key to control the fouling issues during the steady operation of the plant. In this regard, differing between critical or threshold flux patterns in the treatment of wastewater effluents by UF is relevant to confirm the level of fouling expected and to verify if no fouling is predictable or if certain amount of fouling cannot be avoided. In the present study, the hydrodynamic behavior of a polymeric UF membrane was analyzed by means of both critical and threshold flux theories and diverse patterns were found depending on the feedstock pollutants concentration and particle size distribution. Results obtained from the pressure-cycling experiments point for a threshold flux pattern in the case of UF of the effluent derived from the extraction process (OMW) disregarding the applied pretreatment, whereas for 1:1 (v/v) mixture of the latter with the wastewater from the fruit washing (OWW) the membrane fits a critical flux trend, indistinctly of the performed pretreatment too, with negligible fouling below the critical conditions. These conclusions are supported by the experimental permeate flux profiles during batch-run operation experiments.     

Nitrogen stripping to remove dissolved oxygen from extra virgin olive oil

The stripping treatment of extra virgin olive oil (EVOO) by nitrogen gas to remove dissolved oxygen (DO) was tested immediately after the oil production. Dissolved oxygen was measured before and after stripping, as well as one week later along with chemical analyses with the aim to assess the effects of the stripping treatment on EVOO quality. Stripping gave a great reduction of DO, of ca 50%. Both stripped (SO) and non‐stripped (non‐SO) oil samples showed a fast DO consumption up to zero in seven days. At this time, the non‐SO samples showed significant higher peroxide value probably as a consequence of the initial higher DO concentration that gives a greater formation of free radicals. A slightly lower concentration of total phenols was recorded for SO samples. A slight but significant decrease was recorded for only (E)‐hex‐2‐enal concentration within the volatile compounds.     

Treatment of olive mill wastewater by the combination of ultrafiltration and bipolar electrochemical reactor processes

The main purpose of this study was to investigate the removal of the chemical oxygen demand (COD) from olive mill wastewater (OMW) by the combination of ultrafiltration with electrocoagulation process. Ultrafiltration process equipped with CERAVER membrane was used as pre-treatment for electrochemical process. The obtained permeate from the ultrafiltration process allowed COD removal efficiency of about 96% from OMW. Obtained permeate with an average COD of about 1.1 g dm⁻³ was treated by electrochemical reactor equipped with a reactor with bipolar iron plate electrodes. The effect of the experimental parameters such as current density, pH, surface electrode/reactor volume ratio and NaCl concentration on COD removal was assessed. The results showed that the optimum COD removal rate was obtained at a current density of 93.3 A m⁻² and pH ranging from 4.5 to 6.5. At the optimum operational parameters for the experiments, electrocoagulation process could reduce COD from 1.1 g dm⁻³ to 78 mg dm⁻³, allowing direct discharge of the treated OMW as that meets the Algerian wastewater discharge standards (<125 mg dm⁻³).     

Final purification of synthetic olive oil mill wastewater treated by chemical oxidation using ion exchange: Study of operating parameters

In this research work, ion exchange (IE) is presented as a suitable option for purification of olive oil mill wastewater (OMW) previously treated by means of a secondary treatment (OMWST). This pretreatment consisted in Fenton-like oxidation process, followed by coagulation–flocculation and filtration through olive stones. The parametric requirements for drinking water production or at least for public waterways discharge were achieved using a combination of two IE columns working in series at bench scale. The IE resins used in this study were Dowex Marathon C and Amberlite IRA-67. The effect of contact time, operating temperature and flow rate on simultaneous removal of sodium, total iron, chloride and phenols (the major pollutant species in OMWST) were investigated. Removal percentages of sodium, chloride and total iron increased with incrementing the contact time. Equilibrium was obtained in about 30 min for all ions and ion concentrations values determined were lower than the maximum levels for drinking water standards. On the other hand, adsorption efficiencies of sodium, total iron and chloride ions were found to be not considerably affected by the operating temperature. The highest phenols removal percentage (around 100%) was obtained in the first minutes for 298 K and 10 L/h.     

A compact process for the treatment of olive mill wastewater by combining OF and UV/H2O2 techniques

Olive oil production results in important quantities of wastewater containing large amounts of total solids and organic carbon as well as low oil concentrations. This paper describes the treatment of olive mill wastewater (OMW) by combining an ultrafiltration (UF) technique and an advanced oxidation process (AOP) using UV/H₂O₂. It further demonstrates the technical feasibility of this compact and stable process to remove a large part of total solids and organic carbon. Indeed, OF reduces the pollutants contained in the OMW with an apparent rejection coefficient R_COD in the range of 94%. The UV/H₂O₂ oxidation process may be easily used, in combination with UF, to finish the treatment of the permeate. The results obtained in batch and continuous mode showed that this technique offered a treated solution which complies with legal requirements. A final concentration of 17 mg_TOC dm⁻³ was obtained, which corresponds to a final COD of 52 mg dm⁻³, while the legal requirement is 125. Furthermore, the final effluent is fully decolorized.     

Threshold performance of a spiral-wound reverse osmosis membrane in the treatment of olive mill effluents from two-phase and three-phase extraction processes

A reverse osmosis (RO) treatment stage was examined for the complete depuration of the different effluents exiting the olive mill factories (OMW) working with diverse extraction procedures, that is, the two-phase and the three-phase extraction processes, respectively. In the present work, the modelization of batch RO purification of OMW by means of the relevant equations of the threshold flux theory for fouling control and plant dimension is addressed. Results show that higher threshold flux values (20.2–22.1% increase) and major feed recovery rates (80.2–85.0%) as well as very significant reduction of the long-term fouling index (27.3–52.7%) were achieved by using as pretreatment steps the following series of processes: pH-T flocculation, UV/TiO₂ photocatalysis, UF and NF in series. This leads to both lower energy and capital costs, in particular a reduction of the required membrane area in case of batch membrane processes equal to 22.3–44.8%. Accurate prediction of the rejection behavior was attained by the used leaky solution-diffusion model in all cases, with reflection coefficients (σ_COD) ranging from 0.86 to 1.0. The purified effluent streams are finally compatible with irrigation water quality standards (COD values below 1000 mg L⁻¹).     

Screening of Fe–BEA catalysts for wet hydrogen peroxide oxidation of crude olive mill wastewater under mild conditions

A series of Fe–BEA catalysts, differing in the amount of iron have been characterized by XRD, BET surface area, UV–vis spectroscopy and chemical analysis. The zeolite samples have been tested as heterogeneous catalysts for the wet hydrogen peroxide oxidation of crude olive mill wastewaters (OMW) under very mild conditions (at 28 °C and atmospheric pressure). All experiments were performed on a laboratory scale set-up.BSE-1/3 catalyst with a moderate Fe content (Fe/Al = 1.19) showed the best results in terms of catalytic activity and loss of active species into the aqueous solutions. The stability of Fe species has been shown to be strongly dependent on the Fe environment into the zeolite framework.Over the selected catalyst, application of catalytic procedure on diluted OMW solution permitted high removal efficiencies of pollutants. The process produces a removal capacity of 28% of total organic carbon (TOC), 40% of total phenols, 30% of chemical oxygen demand (COD) and 59% of colour, just after 12 h. 5-Day biochemical oxygen demand (BOD₅), and toxicity towards the bioluminescent bacteria Vibrio fischeri were selected to follow the performance of this process in terms of reducing the ecotoxicity of OMW. Results showed an increase in the biodegradability of the treated sample and a decrease of the microtoxicity from 100% to 70% load towards V. fischeri.Occurrence of small catalyst deactivation by carbonaeous during the oxidation reaction was observed through scanning electron microscopy (SEM) and elemental analysis.     

Stabilization of refined olive oil by enrichment with chlorophyll pigments extracted from Chemlali olive leaves

This paper presents the first investigation on the effect of enrichment refined olive oil by chlorophyll pigment extracted from Chemlali olive leaves during storage (6 months). The changes that occurred in the quality indices, fatty acids, sterol, and phenolic content were investigated during the storage of refined olive oil under RT (20°C) and accelerated conditions (50°C) in the dark. Additionally, the pigments (chlorophyll and carotene) changes during 6 months of oil storage were evaluated. At the end of the storage, more than 90% of chlorophyll pigments decomposed in all samples, while, carotene pigment loss was lower showing up to 60 and 85% loss for oil stored at 20 and 50°C, respectively, at the end of storage. The reduction of total phenolic compounds exhibited similar degradation profiles, being reduced by 5% and up to 60% for the enriched refined olive oil stored at 20 and 50°C in 6 months, respectively. In the fatty acid composition, an increase in oleic acid and a decrease in linoleic and linolenic acids were less significant in enriched than non‐enriched refined olive oil. On the other hand, sterol composition was less affected by storage in enriched oil samples. However, the sterol concentration of the oil samples showed an increase in β‐sitosterol, 24‐methylene cholesterol, stigmasterol, and a decrease in cholesterol, Δ5, 24‐stigmastadienol percentage at the end of storage. Based on the Rancimat method, the oils with added leaf pigment extract had the lowest peroxide value and the highest stability. After 6 months of storage, the oxidative resistance of refined olive oil fell to 0.2 and to zero for enriched refined olive oil stored at 20 and 50°C, respectively.     

Effect of aerobic pretreatment on anaerobic digestion of olive mill wastewater (OMWW): An ecoefficient treatment

Anaerobic digestion experiments of olive mill wastewater (OMWW) without pretreatment were carried out and signs of inhibition in the biological process were observed after a time equal to 1.5 times the Hydraulic Residence Time (HRT) due to the presence of a high inhibitors concentration in OMWW. Based on these findings, OMWW was subjected to an aerobic pretreatment in order to reduce the concentration of phenolic compounds and decrease Total Chemical Oxygen Demand (TCOD), achieving a reduction of 78% and 90% of the initial polyphenols concentration and 18% and 21% TCOD reduction when the substrate was aerated for 5 and 7 days respectively.Finally, anaerobic digestion experiments using OMWW aerated for 5 and 7 days as substrate were conducted to determine the influence of aeration time on methane yields and TCOD reduction. The results yield 5 days as the aeration time that achieves best results, given that this stabilizes the anaerobic process, can reduce the TCOD by 65% and generates almost 0.39 m³ methane/kg removed TCOD.Anaerobic digestion of OMWW will be economically feasible if the waste is pretreated by aerobic digestion, since the period of return of investment obtained under these conditions does not exceed 6 years.     

Co-combustion of coal and olive oil industry residues in fluidised bed

Recently new environmental regulations of fossil fuels have further increased interest in the use of waste and biomass for energy generation. Co-combustion is generally viewed as the most cost-effective approach to biomass and wastes utilisation by the electric utility industry.The aim of this paper is to assess the feasibility of co-firing coal and a very specific biomass waste from the olive oil industry: foot cake, in a fluidised bed. This waste is quite difficult material to be used in combustion process, due to its high moisture content and alkaline content in ashes.Two different Spanish coals were selected for this study: a lignite and an anthracite. The combustion tests were carried out in the CIEMAT bubbling fluidised bed pilot plant. In order to study the effect of different parameters on the emissions and combustion efficiency, the tests were done using different operating conditions: furnace temperature, share of foot cake in the mixtures and coal type.The pilot plant tests show that the combustion of foot cake/lignite or anthracite mixtures in bubbling fluidised bed is one way to utilise this biomass residue in energy generation. The presence of foot cake in the mixtures has not any significant effect on the combustion efficiency. SO₂ and NO_x emissions decrease when the amount of foot cake in the mixtures increases, while N₂O emission increases.     

Improving olive oil quality with double protection: Destoning and malaxation in nitrogen atmosphere

Effect of destoning and malaxation in nitrogen atmosphere on oxidative stability, fatty acid and sterol composition of extra virgin olive oil (EVOO) were investigated in industrial scale. Olives of ‘Edremit yaglik’ cultivar were processed with a two phase centrifugal system with or without stones, in nitrogen or air atmosphere. Results have shown that either N₂ flush or destoning did not make any contribution to the sterol and fatty acid composition. Malaxation in nitrogen atmosphere extended induction time, raised phenolic, tocopherol contents and antioxidant potential of oils. Destoning also increased oxidative stability but lowered carotenoid and chlorophyll contents of oils. Among all treatments, the combined effect of destoning and malaxation in nitrogen atmosphere achieved the production of EVOO with the highest quality.