Raw Olive Mill Wastewater Research Articles

Strategies for dephenolization of raw olive mill wastewater by means of Pleurotus ostreatus

The reduction of polyphenols content in olive mill wastewater (OMW) is a major issue in olive oil manufacturing. Although researchers have pointed out the potential of white-rot fungus in dephenolizing OMW, the results available in the literature mainly concern pretreated (sterilized) OMW. This paper deals with the reduction of polyphenols content in untreated OMW by means of a white-rot fungus, Pleurotus ostreatus. Dephenolization was performed both in an airlift bioreactor and in aerated flasks. The process was carried out under controlled non-sterile conditions, with different operating configurations (batch, continuous, biomass recycling) representative of potential industrial operations. Total organic carbon, polyphenols concentration, phenol oxidase activity, dissolved oxygen concentration, oxygen consumption rate, and pH were measured during every run. Tests were carried out with or without added nutrients (potato starch and potato dextrose) and laccases inducers (i.e., CuSO₄). OMW endogenous microorganisms were competing with P. ostreatus for oxygen during simultaneous fermentation. Dephenolization of raw OMW by P. ostreatus under single batch was as large as 70%. Dephenolization was still extensive even when biomass was recycled up to six times. OMW pre-aeration had to be provided under continuous operation to avoid oxygen consumption by endogenous microorganisms that might spoil the process. The role of laccases in the dephenolization process has been discussed. Dephenolization under batch conditions with biomass recycling and added nutrients proved to be the most effective configuration for OMW polyphenols reduction in industrial plants (42-68% for five cycles).

Strategies for lipids and phenolics degradation in the anaerobic treatment of olive mill wastewater

Strategies are proposed for the anaerobic treatment of lipid and phenolic-rich effluents, specifically the raw olive mill wastewater (OMW). Two reactors were operated under OMW influent concentrations from 5 to 48gCODL−1 and Hydraulic Retention Time between 10 and 5 days. An intermittent feeding was applied whenever the reactors showed a severe decay in the methane yield. This strategy improved the mineralization of oleate and palmitate, which were the main accumulated Long-Chain Fatty Acids (LCFA), and also promoted the removal of resilient phenolic compounds, reaching remarkable removal efficiencies of 60% and 81% for two parallel reactors at the end of a feed-less period. A maximum biogas production of 1.4m3m−3d−1 at an Organic Loading Rate of 4.8kgCODm−3d−1 was obtained. Patterns of individual LCFA oxidation during the OMW anaerobic digestion are presented and discussed for the first time. The supplementation of a nitrogen source boosted immediately the methane yield from 21 and 18 to 76 and 93% in both reactors. The typical problems of sludge flotation and washout during the anaerobic treatment of this oily wastewater were overcome by biomass retention, according to the Inverted Anaerobic Sludge Blanket (IASB) reactor concepts. This work demonstrates that it is possible to avoid a previous detoxification step by implementing adequate operational strategies to the anaerobic treatment of OMW.

Anaerobic digestion challenge of raw olive mill wastewater

Olive mill wastewater (OMW) was digested in its original composition (100% v/v) in an anaerobic hybrid. High concentrations (54–55kg COD m−3), acid pH (5.0) and lack of alkalinity and nitrogen are some OMW adverse characteristics. Loads of 8kg COD m−3d−1 provided 3.7–3.8m3 biogas m−3d−1 (63–64% CH4) and 81–82% COD removal. An effluent with basic pH (8.1) and high alkalinity was obtained. A good performance was also observed with weekly load shocks (2.7–4.1, 8.4–10.4kg COD m−3d−1) by introducing piggery effluent and OMW alternately. Biogas of 3.0–3.4m3m−3d−1 (63–69% CH4) was reached.Developed biomass (350days) was neither affected by raw OMW nor by organic shocks. Through the effluents complementarity concept, a stable process able of degrading the original OMW alone was obtained. Unlike what is referred, OMW is an energy resource through anaerobiosis without additional expenses to correct it or decrease its concentration/toxicity.

Detoxification of olive mill wastewaters by zinc–aluminium layered double hydroxides

Disposal of olive mill waste waters (OMWW) represents a serious problem due to its elevated toxicity and pollution risk for environmental and aquatic bodies, which is mainly related to its polyphenol content. The use of layered double hydroxides (LDHs) or anionic clays for OMWW detoxification may represent an effective remediation process. In the current study, OMWW was treated with cold methanol to obtain a dark humic acid-like precipitate made of high molecular weight organic compounds named polymerin and a supernatant made of low molecular weight organics named OMWW-S. After precipitation with methanol, phenol content decreased from 2.14 g L −1 to 0.80 and 1.20 g L −1, in polymerin and OMWW-S, respectively. The chemical oxygen demand of OMWW-S decreased by about 30% with respect to raw OMWW, from 62.2 to 40.2 g L −1. A phenolic concentrate, named OMWW-E was also obtained by ethyl acetate extraction of OMWW-S at pH 2.0. LDHs of zinc and aluminium (LDH) were obtained at room temperature and after calcination at 450 °C (LDH-450). An organo-mineral complex of LDH with polymerin (LDH-Pol) was also synthesised. Phenols from OMWW-E were sorbed preferentially on three matrices according to the following order: LDH-450 > LDH > LDH-Pol, with percent sorption of up to 73% for LDH-450. Repeated cycles of sorption of OMWW-S onto LDH-450 decreased phenol concentration by about 90%. Use of remediated water in a phytotoxicity bioassay revealed scant inhibition of germination and coleoptile elongation rate in tomato seeds and seedlings. Thus, OMWW-S after sorption onto LDH-450 could represent a low cost source of irrigation water for arid soil of the Mediterranean region.

Effect of acclimatization factors on reproducibility of biogas production in anaerobic cultures from electrochemically pre-treated or filtered olive mill wastewater

Olive mill wastewater (OMW) is an agro industrial waste with a high organic load produced mainly in the Mediterranean region. Its inherent toxicity to anaerobic microorganisms is attributed to its high content in COD and phenols. Many treatments have been proposed for the remediation of this waste both physicochemical and biological but there is not one that is applicable in all cases. In this work, olive mill wastewater was treated anaerobically at different growth conditions. The waste introduced in the cultures was either filtered or electrochemically pretreated OMW. Two sets of experiments were conducted to evaluate the effect of temperature, HS-Co-M, fatty acids and OMW pretreatment on biogas production efficiency. The thermophilic growth exhibited extended lag phase compared to the mesophilic growth. Biogas production was strongly dependent on growth supplements. Both HS-Co-M and fatty acids enhanced biogas production in the presence of filtered and electrolyzed OMW. In a second set of experiments, the effect of a mixture of fatty acids was investigated in combination with pretreated or raw OMW.

Assessment of Organic Carbon Removal by Particle Size Distribution Analysis

Particle size distribution (PSD)-based fractionation, an alternative methodology in wastewater characterization, was employed to gather detailed information on the organic matter content of a raw olive mill wastewater (OMW) and to investigate the changes brought about in this characteristic after application of certain chemical treatment alternatives, namely, lime precipitation–coagulation, Fenton oxidation, and electrocoagulation. PSD-based analysis of the untreated OMW demonstrated that more than two-thirds of its organic carbon content, measured as chemical oxygen demand (COD) (69%), total organic carbon (TOC) (74%), as well as antioxidant activity (AOA) (74%) caused by the polyphenolic carbon fraction, was at the soluble range (<2 nm). Treatability experiments, with maximum overall removal efficiencies below 50% even under optimized conditions, indicated that none of the applied chemical pretreatment methods was sufficiently effective in removing the organics from the investigated OMW. Nonetheless, PSD-based fractionation of the pretreated samples provided an insight about the treatment alternatives and the size fractions where they performed better. Electrocoagulation was capable of removing particulate and colloidal matter and provided a relatively higher overall performance with 23, 20, and 34% decreases in COD, TOC, and polyphenol contents of the OMW, respectively. Fenton process, on the other hand, showed a lower overall performance in terms of COD and TOC removal (17 and 15%, respectively), yet it was significantly effective on the soluble fraction, and thus more successful in removing the polyphenols mostly originating from the soluble range, with an overall efficiency of 42%. Based on these observations, PSD analysis was suggested as a useful tool to perform detailed wastewater characterization, as well as to differentiate between specific impacts of different pretreatment processes and help choose between alternatives, especially when a particular pollutant is targeted.

Characterization of the harmful effect of olive mill wastewater on spearmint

In this study, changes in viability, biomass production, essential oil yield and essential oil composition of Mentha spicata L. (spearmint) exposed to olive mill wastewater (OMW) were investigated. Spearmint cuttings were sensitive to OMW and, after 6 h of incubation in raw or diluted OMW, their viability was null. The short contact of raw OMW with mint cuttings caused an irreversible damage in rhizogenesis and shoots development. Roots were more sensitive to phytotoxicity than shoots. In a field essay, spearmint showed a good capability to recover when OMW was spread at 8 l m −2 at the vegetative phase of growth (45 days after plantation). At this dose, a slight increase of mostly of the mint essential oil constituents was obtained. When the dose applied was 16 l m −2, phytotoxicity was manifested by a high reduction of biomass and essential oil yield. The essential oil composition was also affected and a disappearance of many of mint essential oil constituents was observed with an increase of 59% for carvone, the major compound of spearmint essential oil. As far as we know, this is the first report on the effect of field application of OMW on an aromatic plant essential oil yield and composition.

Anaerobic digestion of olive mill wastewater in a periodic anaerobic baffled reactor (PABR) followed by further effluent purification via membrane separation technologies

AbstractBACKGROUND: The combined treatment of olive mill wastewater (OMWW) by applying the anaerobic digestion process and further treatment in a system consisting of filters and membranes is presented. The anaerobic digestion of the OMWW took place in a high rate system, the periodic anaerobic baffled reactor (PABR). Application of the membrane system aimed at purifying the anaerobic effluent.RESULTS: An increase in the organic loading rate was achieved by increasing the influent chemical oxygen demand (COD) and alternatively by decreasing the hydraulic retention time (HRT). The first option caused process failure, since the volatile fatty acids accumulation resulted in negligible biogas production. In contrast, the second change (decrease in HRT) led to stable operation that permitted the reduction of the HRT to 3.75 d and increase of the organic loading rate to 8.9 g tCOD L−1 d−1 with satisfactory total COD removal (72%). Higher total COD removal (up to 80%) was observed at lower organic loading rates (&lt;3.5 g tCOD L−1 d−1). Further purification in the membrane units resulted in a final permeate of less than 0.1 g tCOD L−1. The membrane systems proved to be more efficient on the anaerobic effluent than on the raw OMWW (the final permeate in that case contained 1g tCOD L−1).CONCLUSIONS: The anaerobic digestion of OMWW in a PABR was stable even at high organic loading rates. Filtering and membrane fractionation of the PABR effluent resulted in a final permeate stream of high quality, suitable for irrigation and/or reuse in the proposed operating scheme for diluting the OMWW prior to anaerobic digestion. Copyright © 2009 Society of Chemical Industry

Effect of clay pretreatment on photofermentative hydrogen production from olive mill wastewater

The aim of this paper was to gain further insight into the effect of the clay pretreatment process on photofermentative hydrogen production. This two-stage process involved a clay pretreatment step followed by photofermentation which was performed under anaerobic conditions with the illumination by Tungsten lamps. Rhodobacter sphaeroides O.U.001 was used for photofermentation. Higher amounts of color (65%), total phenol (81%) and chemical oxygen demand (31%) removal efficiencies were achieved after clay pretreatment process. During photofermentative hydrogen production with the effluent of clay pretreatment process, the main organic compounds resulting higher hydrogen production rates were found to be acetic, lactic, propionic, and butyric acids. Compared to photofermentation using raw olive mill wastewater (16LH2/LOMW), the amount of photofermentative hydrogen production was doubled by using the effluent of the clay pretreatment process (31.5LH2/LOMW). The reasons for the improvement of hydrogen production by clay treatment can be attributed to the high removal of the hardly biodegradable compounds such as phenols; minor removal of organic acids, sugars and amino acids that are known to enhance photofermentative hydrogen production; and the color depletion of raw OMW which might cause a shadowing effect on the photosynthetic bacteria.

Production of Triacetylhydroxytyrosol from Olive Mill Waste Waters for Use as Stabilized Bioantioxidant

A hydroxytyrosol triacetyl derivative was very efficiently produced as a highly pure stabilized antioxidant compound by a short treatment of olive mill waste water (OMWW) organic extracts, rich in hydroxytyrosol, with an acetylating mixture composed of HClO4-SiO2 and Ac2O (Chakborti and Gulhane reaction), in mild and safe conditions. A successive single step of middle pressure liquid chromatography (MPLC) purification of the reaction product was performed, with an overall yield of 35.6%. (This process, including both the Chakborti and Gulhane reaction and the MPLC purification, is protected by an international patent under PCT/IT2005/000781.) The o-diphenol triacetyl derivative was also produced by direct reaction of hydroxytyrosol, previously purified by MPLC, with HClO4-SiO2 and Ac2O, with an overall yield of 29.5%. A further procedure for the production of the hydroxytyrosol triacetyl derivative was consistent with the direct treatment of raw OMWW with the acetylating agent and a single step of MPLC purification, with an overall yield of 27.6%. The purified natural triacetylhydroxytyrosol confirmed the same strong protective effects against the oxidative stress in human cells as the corresponding synthetic compound, likely because of the biochemical activation of the acetyl derivative into the active parent hydroxytyrosol by esterases. We therefore propose the utilization of OMWW for recovering hydroxytyrosol as a natural antioxidant in a chemically stabilized form, with a good yield, which can be potentially used as a nontoxic functional component in nutritional, pharmaceutical, and cosmetic preparations.

Olive mill wastewater treatment: an experimental study

Olive oil production, one of the main agro-industries in Mediterranean countries, generates significant amounts of olive mill wastewaters (OMWs), which represent a serious environmental problem, because of their high organic load, the acidic pH and the presence of recalcitrant and toxic substances such as phenolic and lipidic compounds (up to several grams per litre). In Italy, traditional disposal on the soil is the most common way to discharge OMWs. This work is aimed at investigating the efficiency and feasibility of AOPs and biological processes for OMW treatment. Trials have been carried out on wastewaters taken from one of the largest three-phase mills of Italy, located in Quarrata (Tuscany), as well as on synthetic solutions. Ozone and Fenton's reagents applied both on OMWs and on phenolic synthetic solutions guaranteed polyphenol removal efficiency up to 95%. Aerobic biological treatment was performed in a batch reactor filled with raw OMWs (pH = 4.5, T = 30 degrees C) without biomass inoculum. A biomass rich of fungi, developed after about 30 days, was able to biodegrade phenolic compounds reaching a removal efficiency of 70%. Pretreatment of OMWs by means of oxidation increased their biological treatability.

Detoxification of olive mill wastewater by electrocoagulation and sedimentation processes

Olive mill wastewater (OMW) is characterised by its high suspended solids content (SS), high turbidity (NTU), chemical oxygen demand (COD) concentration up to 100 g l −1 and toxic phenolic compounds concentration up to 10 g l −1. This study examined the effect of a physico-electrochemical method to detoxify olive mill wastewater prior an anaerobic biotreatment process. The proposed pre-treatment process consisted in a preliminary electrocoagulation step in which most phenolic compounds were polymerised, followed by a sedimentation step. The BOD 5/COD ratio of the electrocoagulated OMW increased from 0.33, initial value, to 0.58. Furthermore, the sedimentation step yielded the removal of 76.2%, 75% and 71% of phenolic compounds, turbidity and suspended solid, respectively, after 3 days of plain settling. The combination of electrocoagulation and sedimentation allowed a COD reduction and decoloration of about 43% and 90%, respectively. This pre-treatment decreases the inhibition of Vibrio fisheri luminescence by 66.4%. Continuous anaerobic biomethanization experiments conducted in parallel with raw OMW and electrocoagulated OMW before and after sedimentation at a loading rate of 6 g COD l −1 day −1, proved that the final pre-treated OMW was bioconverted into methane at high yield while raw OMW was very toxic to anaerobic microorganisms.

Olive mill wastewater remediation by means of Pleurotus ostreatus

Results of a research program on raw olive-mill wastewater (OMW) bioremediation are presented. Bioremediation experiments have been carried out both in an airlift bioreactor and in aerated flasks, using Pleurotus ostreatus. The process was investigated under controlled non-sterile operating conditions, representative of industrial operation. Growth of P. ostreatus as well as polyphenols conversion were assessed. OMW bioconversion was characterized in terms of total organic carbon, polyphenols concentration, phenol oxidase activity, extent of decolourization and pH as a function of time. Results demonstrate that: P. ostreatus effectively grows on raw OMW; polyphenols abatement is controlled by the availability of nutrients and can be as large as 95%; bioconversion of non-sterilized OMW does not result into appreciable decolourization of the liquid medium. The use of an internal loop airlift bioreactor as a candidate for the full-scale implementation of an OMW aerobic bioremediation process is demonstrated.

Biomass Selection for Optimal Anaerobic Treatment of Olive Mill Wastewater

This research was conducted to identify the most efficient biomass out of five different types of biomass sources for anaerobic treatment of Olive Mill Wastewater (OMW). This study was first focused on examining the selected biomass in anaerobic batch systems with sodium acetate solutions (control study). Then, the different types of biomass were tested with raw OMW (water-diluted) and with pretreated OMW by coagulation-flocculation using Poly Aluminum Chloride (PACl) combined with hydrated lime (Ca(OH)2). Two types of biomass from wastewater treatment systems of a citrus juice producing company "PriGat" and from a citric acid manufacturing factory "Gadot", were found to be the most efficient sources of microorganisms to anaerobically treat both sodium acetate solution and OMW. Both types of biomass were examined under different concentration ranges (1-40 g l-1) of OMW in order to detect the maximal COD tolerance for the microorganisms. The results show that 70-85% of COD removal was reached using Gadot biomass after 8-10 days when the initial concentration of OMW was up to 5 g l-1, while a similar removal efficiency was achieved using OMW of initial COD concentration of 10 g l-1 in 2-4 days of contact time with the PriGat biomass. The physico-chemical pretreatment of OMW was found to enhance the anaerobic activity for the treatment of OMW with initial concentration of 20 g l-1 using PriGat biomass. This finding is attributed to reducing the concentrations of polyphenols and other toxicants originally present in OMW upon the applied pretreatment process.

The effect of olive mill wastewater on seed germination after various pretreatment techniques

Olive mill wastewater (OMW) management has been a major issue of environmental concern for olive oil producing countries. OMW can be a serious nuisance, when disposed of untreated, due to its significantly high organic load, its phytotoxic properties and its relatively low biodegradability. Field and plant irrigation with raw or pretreated OMW is an easy and relatively inexpensive method to treat and dispose of OMW. Typical pretreatment techniques could be comprised of phase separation through a settling basin, dilution with water, aeration to promote biological degradation and pH neutralization. A full factorial experimental design approach was used here to study the main effects and interactions of the above four pretreatment techniques on the germination of tomato and chicory seeds. Results of the study showed that the most statistically significant technique affecting OMW phytotoxicity is water dilution. The next most significant technique was aeration. In particular, phytotoxicity decreased with increased OMW dilution with water, when OMW was aerated and without pH adjustment. pH neutralization resulted in increased phytotoxicity. Settling did not significantly decrease the phytotoxicity of settled OMW and is therefore not considered necessary in an OMW management system in which plant irrigation is the goal. The interaction of aeration and pH was, marginally, the most significant two-way interaction for tomato seeds, while no interactions were significant when chicory seeds were used.

Reduction of the phenolic components in olive-mill wastewater by an enzymatic treatment and its impact on durum wheat ( Triticum durum Desf.) germinability

Olive-mill wastewater (OMW), an effluent of olive oil extraction process, is annually produced in huge amounts in olive growing areas. An interesting option for its disposal is the spreading on agricultural land, provided that phytotoxic effects are neutralized. The objective of the present investigation was to evaluate the potential of an enzyme-based treatment in removing OMW phytotoxicity. To this aim, germinability experiments on durum wheat ( Triticum durum Desf. cv. Duilio) were conducted in the presence of different dilutions of raw or enzyme-treated OMW. OMW treatment with laccase resulted in a 65% and 86% reduction in total phenols and ortho-diphenols respectively, due their polymerization as revealed by size-exclusion chromatography. Raw OMW exerted a significant concentration-dependent inhibition on the germinability of durum wheat seeds which was evident up to a dilution rate of 1:8. When the effluent was treated with a fungal laccase, germinability was increased by 57% at a 1:8 dilution and by 94% at a 1:2 dilution, as compared to the same dilutions using untreated OMW. The treatment with laccase also decreased the mean germination time by about 1 day as compared to untreated controls. These results show that germinability inhibition due to OMW can be reduced effectively using fungal laccase, suggesting that phenols are the main determinants of its phytotoxicity.

Edible mushrooms from olive oil mill wastes

The biological remediation of olive oil mill wastes has been attempted several times in the past through the use of different types of microbes. Among them, a relatively large array of fungi were studied for neutralizing the heavy pollutant effects and/or for converting these wastes into new value-added products. The present investigation was aiming at examining whether olive oil mill wastes could be exploited for the cultivation of mushrooms of the genus Pleurotus. At a preliminary stage, two Pleurotus species, i.e. P. eryngii and P. pulmonarius, were tested for their ability to colonize an olive press-cake (OPC) substrate supplemented with various dilutions of raw olive mill wastewater (OWW). Some important cultural characters related to mushroom production (earliness, yield, biological efficiencies and quality of basidiomata) were estimated. The outcome revealed different cultural responses for each Pleurotus species examined; the P. pulmonarius strain showed better earliness values and P. eryngii, although it was a slow growing fungus, produced basidiomata in high yields and of a very good quality. On the other hand, the OPC substrate supplemented with low concentrations of OWW (12.5% v/w) behaved satisfactorily as regards the fungal colonization rates and mushroom yield, but when the addition of higher rates of raw, untreated OWW (75–100% v/w) was attempted then the Pleurotus strains were completely unable to grow. The optimal concentration of OWW for Pleurotus mycelial growth was assessed through measurements of the biomass produced in liquid nutrient media and was found to lie within the 25–50% range, depending on the Pleurotus species and on the properties of the substrates examined. Furthermore, the phytotoxic effects that the spent liquid medium possessed were examined in comparison with the phytotoxicity of the raw liquid waste. The prospects of exploiting olive oil mills wastes for mushroom cultivation is discussed.