Electrochemical treatment of olive mill wastewaters: Removal of phenolic compounds and decolourization

Olive mill wastewaters (OMW) characterized by their dark brown colour and their very high content of phenolic compounds constitute an environmental concern, particularly in Mediterranean countries where the production of olive oil is important. In this investigation, OMW were electrolyzed at platinized expanded titanium electrodes in a modified Grignard reactor divided into two cylindrical compartments separated by a cation-exchange membrane. Results show better than 90% decolourization and nearly 85% removal of phenols, as established by gas chromatography/mass spectrometry, at high current intensity. This process can easily be monitored by cyclic voltammetry at a boron-doped diamond electrode. A significant reduction of chemical oxygen demand and total organic carbon was observed. The electrodes are not passivated and the ohmic potential drop is very low. Electrochemical oxidation in a modified Grignard reactor is a promising process for the destruction of phenolic compounds present in OMW.     

Treatment of wastewaters from the olive mill industry by sonication

BACKGROUND: In this study, the effects of additives (manganese (III) oxide (Mn₃O₄), Cu⁺², Fe⁰ and potassium iodate (KIO₃)) and radical scavengers (sodium carbonate (Na₂CO₃), perfluorohexane (C₆F₁₄) and t‐buthyl alcohol (C₄H₁₀O)) on the dephenolization, decolorization, dearomatization and detoxification of olive mill wastewater (OMW) by sonication were investigated because wastewaters from this industry are not removed effectively. RESULTS: The maximum COD, color, total phenol and total aromatic amines (TAAs) removal efficiencies were 63, 82, 78 and 71%, respectively, at 60 °C with sonication only. The TAAs and phenol yields were increased to 96 and 97% with 6 mg L^?1 KIO₃ and 3 mg L^?1 Fe⁰ while color removal reached 97% with 6 mg L^?1 C₆F_14. The total annual cost with sonication only was 665 € m^?3 year^?1 while the cost slightly increased (666€ m³ year^?1) with C₆F₁₄. The maximum acute toxicity removals were 97‐98% in Daphnia magna and Vibrio fischeri The Microtox acute toxicity test was more sensitive than the Daphnia magna to the OMW samples. CONCLUSION: COD, color, total phenol, TAAs and toxicity in an OMW were removed efficiently and cost‐effectively by sonication. © 2012 Society of Chemical Industry     

Anaerobic digestion of Aegean olive mill effluents with and without pretreatment

BACKGROUND: Olive oil production is an important economical activity in the Aegean region of Turkey. However, the effluents of the olive oil producing mills with their high organic loads and toxic compounds are causing serious environmental problems. The anaerobic biological treatment of olive mill wastewater (OMWW) using the treatment plants of the regional industries could be a method of choice and within the scope of this study floccular and granular sludges were investigated in batch mode for their success in the treatment of OMWW while producing biogas. The major limitation of this treatment is the inhibition of methanogenic bacteria by the phenolic compounds in OMWW. Thus an integrated solution was suggested in which a pre‐treatment step (dephenolization) was also introduced before biological step. RESULTS: The effluents of 27 olive mills out of 47 were found to have total phenolics (TP) less than 3 g L^?1 and could be treated anaerobically after simple dilution. The biogas production for the untreated OMWW was higher for floccular sludge than for the granular sludge (68.5 mL and 45.7 mL respectively). Combined pre‐treatment experiments, first coagulation with polyaluminum chloride, followed by flocculation with cationic polyelectrolyte and finally Fenton's oxidation, could remove 80% of TP and 95% of the total suspended solids. CONCLUSION: OMWW having TP values less than 3 g L^?1 can be treated anaerobically using floccular sludge after simple dilution and biogas can be produced. For OMWW samples having higher TP values pre‐treatment is necessary and the pre‐treatment given in this study may be used effectively. Copyright © 2010 Society of Chemical Industry     

Electrochemical treatment of olive mill wastewater

Background Olive mill wastewater (OMW) constitutes a very strong agro‐industrial wastewater posing severe environmental threats in olive oil producing countries. The main objective of this study was to treat olive mill wastewater by electrochemical oxidation. The variables studied included the type and concentration of electrolyte solutions, voltage and time applied. Results: The electrolyte type and concentration significantly affected the degradation efficiency of the electrochemical oxidation. Optimal conditions for NaCl concentration were 3% (w/v) and 16 V. At these conditions chemical oxygen demand (COD) removal reached 70.8% after 8 h of electrochemical treatment, while color and turbidity were completely removed after short periods of treatment. However, bio‐assays indicated that the ecotoxicity of the treated wastewater remained unchanged, possibly due to the formation of chlorinated by‐products. Na₂SO₄ did not demonstrate sufficient efficiency. The simultaneous use of FeCl₃ and NaCl contributed to electro‐coagulation of OMW. After settlement, two separate phases were formed: the supernatant phase and the settled solids. Under optimal conditions (2% Na₂SO₄ + 1% FeCl₃; 24 V), the removal efficiency of COD reached 85.5% at the supernatant phase. Conclusion: NaCl was an effective electrolyte for OMW treatment. The electro‐coagulation process was also a successful process, but as in the case of NaCl the remaining acute toxicity of treated OMW was high. Copyright © 2007 Society of Chemical Industry     

Screening of white rot fungi for the treatment of olive mill waste-waters

Several white rot fungi were evaluated for their ability to decolorize olive mill waste-waters (OMW). Among these, Phanerochaete chrysosporium showed the highest potential for the biological depollution of OMW. Approximately 65% of the color and 73% of the chemical oxygen demand (COD) were removed by P. chrysosporium strain HD. Phlebia radiata, Dichomitus squalens, Polyporus frondosus and Coriolus versicolor could also decolorize the OMW but to a lesser extent. The different abilities of these white rot fungi to decolorize OMW correlated with their rates of depolymerization of high molecular weight aromatics and the degradation of the low molecular weight aromatic compounds. Fourteen strains of P. chrysosporium were compared on the basis of their lignin peroxidase (LiP) production, OMW decolorization and residual material dry weight. High lignin peroxidase producer strains, such as strains HD and BKM-F-1767, showed the highest rates of OMW decolorization, P. chrysosporium strains 79–36 and FP 104297 (low LiP producer strains) did not exhibit any decolorization activity.     

Sustainability analysis and benchmarking of olive mill wastewater treatment methods

A large number of publications are available in the literature regarding olive mill wastewater treatment methods. However, none of the proposed methods can be considered as a best available method in terms of its effectiveness, and its environmental and economic impact. Using a literature survey, data were collected and evaluated in order for a sustainability and benchmarking analysis to be developed. Physicochemical, biological and advanced oxidation methods were evaluated and judged in terms of their effectiveness, environmental impact and cost. Effectiveness of each method was estimated in terms of COD and phenolic compounds reduction, environmental impact in terms of CO₂ production, while for the economic impact the operational costs were taken into account. Finally, a procedure is suggested for selection of the most appropriate method based on user preferences (in terms of effectiveness, environmental impact and cost). The present analysis showed that the most effective processes in terms of organics reduction are membrane filtration, electrolysis, supercritical water oxidation and photo‐Fenton. Lower environmental impact was found with anaerobic digestion, coagulation and lime processes, while the lowest cost category involves biocomposting and membrane filtration, thanks to the exploitation of byproducts (biocompost and phenolic compounds, respectively). © 2013 Society of Chemical Industry     

Toxic effect of coloured olive compounds on the anaerobic digestion of olive oil mill effluent in UASB-like reactors

Anaerobic sludge digestion of olive oil mill effluent (OOME) in Upflow Anaerobic Sludge Blanket (UASB) reactors was shown to be unstable as a result of both chemical and biological parameters. The study was complicated by the fact that Chemical Oxygen Demand (COD) was removed by growth and maintenance of active biomass and by adsorption in and on the sludge. Coloured compounds caused an inhibition effect on the anaerobic digestion of the wastewater. This inhibition, shown at low COD concentrations of diluted OOME, was due to accumulation of recalcitrant coloured compounds in the sludge, inducing irreversible inhibition of bacterial growth. Partial decolourization of OOME through resin (Duolite XAD 761) treatment reduced the toxic effect.     

Treatment of olive mill washing water by ultrafiltration

Olive oil production requires important quantities of washing water containing low oil concentrations, but classical processes used to recover or to eliminate this oil are ineffective. This study presents a membrane technique to treat olive oil mill washing water using different commercial ultrafiltration membranes: one organic (PCI) and two ceramic (Ceraver) membranes. The influence of the hydrodynamic parameters (transmembrane pressure and flow rate) and the cut‐off membranes on the efficiency of the ultrafiltration process was evaluated, and it was shown the organic PCI membrane could reduce pollution due to organic matter by decreasing the value of the Chemical oxygen demand by about 90%. Moreover, the nature of the ultrafine pore membrane appeared to be an important parameter which may strongly increase or decrease the capacity of the membrane. The membrane cut‐off did not have a strong influence on the performance of the process but if the membrane pores were too large the stability of the dynamically formed membrane decreased at transmembrane pressures greater than 0.2 MPa.     

Polyacrylamide-induced coagulation process removing suspended solids from palm oil mill effluent

Palm oil mill effluent (POME) is a colloidal suspension with 2–4% suspended solids. About 50% of the suspended solids are cellulosic compounds, which are not degraded in the typical biological treatment systems. Chemical (polymer-induced coagulation) and physical (settling) pretreatment methods were examined to remove the suspended solids in this study. A novel physicochemical treatment with high water recovery and sludge compressibility including three cationic polyacrylamides (C-PAM; as coagulant) and three anionic polyacrylamides (A-PAM; as flocculant) with different molecular weights and charge densities was used. The coagulants used were biodegradable. The combination of a C-PAM (Chemfloc1515C) with medium molecular weight and charge density and an A-PAM (Chemfloc 430A) with high molecular weight and charge density at doses of 300 and 50 mg/dm³ showed the best total suspended solids (TSS) and chemical oxygen demand (COD) removal (96.4 and 70.9%, respectively). The optimal condition was found at pH 5, rapid mixing at 150 rpm for 1 min, and slow mixing at 40 rpm for 30 s. As a conclusion, the physiochemical pretreatment using biodegradable coagulants was a promising alternative to effectively separate TSS (96.4%) with high water recovery (76%).     

A full‐scale system for aerobic biological treatment of olive mill wastewater

Olive mill wastewater (OMW) is a major environmental problem in the Mediterranean basin. Although many methods for OMW treatment have been developed, only a few have been adopted in pilot‐ or full‐scale applications. A full‐scale system for aerobic biological treatment of OMW was developed. The system consists of a trickling filter and a recirculation tank. Continuous recirculation of the wastewater was used to provide oxygen concentrations from 0.7 to 1.2 mg L^?1. Low ambient temperatures did not affect system performance since the raw wastewater was warm enough. Nutrient addition was not necessary as raw wastewater contained sufficient nitrogen and phosphorous concentrations. Indigenous olive pulp bacteria proved to be resistant to full‐scale conditions. Feed chemical oxygen demand and phenolic concentrations were about 43 000 and 9500 mg L^?1, respectively. The system reduced more than half of the organic load under continuous operation and a hydraulic retention time of 24 h. The efficiency of this method could be improved by combining it with another technology to further reduce the organic load. The absence of mechanical aeration and the very low hydraulic retention time denotes that the proposed system could be viable and attractive. Copyright © 2011 Society of Chemical Industry     

Microbial and toxic evaluation of raw and treated olive oil mill wastewaters

BACKGROUND: Olive oil mill wastewaters (OMW) from a three‐phase system were treated in a laboratory‐scale continuous stirred tank reactor (CSTR) for hydrogen production. Microbiological and physicochemical characterizations of raw and anaerobically treated olive oil mill effluents were performed. Toxicity assessment was also conducted in order to determine the impact of residual waters on the aquatic environment. RESULTS: Pseudomonas aeruginosa that has the ability to utilize phenolic compounds was isolated in raw OMW, along with several gram‐negative bacteria (Serratia odorifera, Enterobacter cloacae and Aeromonas hydrophila). The dominant species in the untreated effluent appears to be Enterobacter cloacae, whereas in the treated effluent it is Citrobacter braakii. Phenols, pH, NO^?₂, total dissolved solids (TDS) and conductivity were the main parameters related to the observed toxicity. CONCLUSION: A significant differentiation in the microbiological flora was detected between treated and untreated effluents whereas the microbial communities were correlated to the toxicity test results, pointing to the need for further research regarding identification of the microbial flora. This can improve the treatment processes to optimize management of OMW for environmentally safe discharge. Copyright © 2010 Society of Chemical Industry     

还原橄榄T的间接电还原法

本工作采用循环伏安法和正交电解实验法研究了还原橄榄T在Fe-TEA媒质中的电化学行为。Fe(III)-TEA络合物在碱性环境下表现出良好的电化学活性,能够还原橄榄T而不会引起过度还原。此外,通过L9(34)正交实验分析了电流密度、温度、媒质浓度和NaOH浓度四因素对电流效率的影响。结果表明在本实验所设条件范围内,最高电流效率可达59.03%,对电流效率影响最大的因素为电流密度。     

Preparation of activated carbon from olive mill solid residue

A process was developed for producing high quality activated carbon from Algerian mill waste. The solid olive mill residue was carbonized at 800 °C and physically activated with CO₂, air or steam. An optimum activation temperature of about 850 °C was determined for all the activation agents used. Steam appeared to be the most efficient activator as compared with air and CO₂. An optimal activation time of about 2 h was then determined with steam as the optimum activation agent. The porous structure of the activated carbon was characterized by nitrogen adsorption at −196 °C, and in all cases the surface areas, calculated by DR and BET methods, confirmed the production of a material with good microstructural characteristics and specific surfaces exceeding 1500 m² g⁻¹ for the carbon prepared by steam activation. Phenol adsorption isotherms gave the adsorption properties and the adsorption capacity of about 11.24 mg of phenol per gram of the activated carbon produced. The kinetics of the phenol adsorption onto the porous material was evaluated by means of two models: the external resistance model and the linear model. The second model appeared to constitute a more appropriate fit for the experimental data. © 2000 Society of Chemical Industry     

Use of Aspergillus niger to improve filtration of olive mill waste-waters

The high levels of dry matter (70–200 g dm^?3) and total suspended solids (TSS) of up to 50 g dm^?3 which are present in olive mill waste-waters (OMW) render these very difficult to filter. During filtration of the OMW viscous solution, a cake is formed by the TSS which decreases the kinetics of the process. Addition of pellets of the fungus Aspergillus niger modifies the cake porosity and thus improves the OMW filtration process. Improvement to the filtration is directly related to the quantity of A, niger added and is attributable to the fermentation of OMW by A. niger since the TSS are trapped by the fungal pellets. The degradation of pectin by A. niger pectinases may also be partly responsible for the increase in the filtration capacity.     

Decolorization of olive oil mill effluent by physical and chemical treatment prior to anaerobic digestion

Chemical and physical treatment of olive oil mill effluent (OOME) was performed using iron and lime as complexing agents, Duolite XAD 761 resin as phenolic adsorbent and hydrogen peroxide as oxidant. We have shown that 10 g dm⁻³ of ammonium iron(III) sulphate·12H₂O, or calcium dihydroxide were sufficient to precipitate more than 50% of the initial COD and remove 50% of the initial colour within a short contacting time. The aromatic adsorbent resin retained more than 50% of the colouring compounds (chromophores) corresponding to removal of more than 60% of the initial COD after treating three bed volumes of crude OOME. The efficiency depended on the volume treated. Hydrogen peroxide removed the substituents of the aromatic rings which resulted in a decrease in length of the colouring compounds in OOME. However, they were not completely degraded, leading to shorter wavelength absorption. This chemical treatment was efficient in colour removal but only 19% COD removal was possible. In all cases, simple aromatics were reduced, as determined by GPC analysis. The chemical and physical decolorization of OOME was efficient in reducing the toxic effect of recalcitrant compounds. The resultant OOME by each of these alternative treatments was readily degradable through anaerobic digestion. © 1998 Society of Chemical Industry     

The use of olive mill wastewater by wild type Yarrowia lipolytica strains: medium supplementation and surfactant presence effect

BACKGROUND: The aim of this work was to study the ability of two different wild type strains of the yeast Yarrowia lipolytica to grow on olive mill wastewater (OMW) and their potential to produce high‐value products such as lipases. Factors that affect cellular growth and OMW degradation were studied, such as nitrogen supplementation, cells concentration and surfactant addition. RESULTS: Both strains, W29 and IMUFRJ 50682, were able to grow in OMW with 19 g L^?1 of COD and approximately 800 mg L^?1 of total phenols concentration. The strain W29 presented the highest potential for extracellular lipase production in OMW medium. Lipase productivity was improved by the medium supplementation with ammonium sulphate up to 6 g L^?1, leading to 80% of COD degradation and 70% of total phenols reduction. The surfactant Tween 80 enhanced cell growth and COD degradation, but had a negative effect on lipase activity. CONCLUSIONS Y. lipolytica has a great potential for OMW valorisation by its use as culture medium for biomass and enzymes production. The operating conditions that favoured lipase production differ from the conditions that improve COD reduction. Copyright © 2008 Society of Chemical Industry     

Treatment of bleaching Kraft mill effluents and polychlorinated phenolic compounds with ozonation

The effect of the simultaneous use of ozone, UVA or visible light, and small quantities of Fe(II)/Fe(III) ions in solution on the degradation rate of the organic content of a bleaching Kraft mill effluent was investigated. The same treatment was applied to synthetic samples of polychlorinated phenolic compounds, because these are one of the main groups of compounds found in real bleaching Kraft mill effluents. In order to improve the treatment efficiency and to lower the cost of the process several other strategies were investigated. It was found that a previous irradiation of the wastewater or the synthetic sample in the absence of ozone significantly improves the rate of removal of organic pollutants during the subsequent ozonation step. © 2002 Society of Chemical Industry