WO2005003037A1

WO2005003037A1 - A method for the treatment of olive mill waste waters

Info

Publication number: WO2005003037A1
Application number: PCT/IB2004/002215
Authority: WO
Inventors: Elias Castanas; Nicolaos Andricopoulos; George Mposkou; Joseph Vercauteren
Original assignee: EMERGO (CYPRUS) Ltd
Current assignee: EMERGO (CYPRUS) Ltd
Priority date: 2003-07-08
Filing date: 2004-07-06
Publication date: 2005-01-13
Anticipated expiration: 2006-01-08
Also published as: GR20030100295A; WO2005003037B1

Abstract

A system of filters for use in the treatment of olive mill waste waters is disclosed as well as a method in which said system of filters is used. The profitable outcome of using said system of filters in the treatment of olive mill waste waters is an effluent which may be used for agricultural irrigation and the retention and recovery of highly valuable products present in the waste waters to be treated.

Description

A METHOD FOR THE TREATMENT OF OLIVE MILL WASTE WATERS

The present invention relates to a system of filters for use in the treatment of olive mill waste waters. Said system of filters is composed of a combination of sub stratums of natural products selected from the group consisting of turf, sand, and sawdust, and optionally one or more filters of resins selected from the group consisting of cationic, mixed-bed, and PVPP resins. Furthermore, the present invention relates to a method for the treatment of olive mill waste waters using said system of filters, and the uses of the effluent obtainable by said method for agricultural irrigation. Finally, the- present invention relates to retention and recovery of highly valuable products, such as antioxidant biophenols, which are present in the waste waters to be treated by use of said system of filters.

Background of invention The rapid expansion of the agro-industry during recent decades has led to the increased production of organic wastes. One such agro-industrial waste is olive mill wastewater (OMWW) , formed by the tissue water from the olive fruits, the water added during the process of oil extraction, soft tissues from olive pulp and oil, in the form of a very stable emulsion. Great amounts of OMWW are produced in Medi- terranean countries, where this waste imposes a great environmental hazard, if it is not treated, due to its very high organic COD loads. The elimination and/or treatment of OMWW is one of the main problems faced by processing companies involved in the extraction of^' olive oil, because they contain^' powerful .pollutants [1] . This waste is an acidic (pH<5) , malodor- ous liquid that contains potassium and phosphatic salts and organic substances such as fats, protein, sugars, organic acids, and polyp enols. Moreover, suspended matter consisting of olive pulp, mucilage, pectin, and oil in a relatively stable emulsion is also present. The amount of OMWW produced, and therefore the environmental impact, varies depending on the method of olive oil extraction used. In fact, the traditional press method produces -50% of OMWW relative to the initial weight of the olives, whereas the continuous . process produces 80-110% of OMWW due to the continuous washing of • the olive paste with .warm water before oil separation from the paste. The treatment and disposal of waste waters are critical problems, especially in the Mediterranean area, where olive cultivation is widespread and a large volume of the effluent (800000 m³/year in Italy alone) is produced and concentrated within a period of only a few months (from November to February) . For these reasons, increasing attention has been given to finding the best methods to distribute OMWW on agricultural lands and to recycle both organic matter and nutritive elements in the soil-crop system [2] or to recover products of biological interest, such as polyphenols. These phenolic compounds are either originally present in the olive fruit [3] or formed during processing of olive oil extraction. The phenolic compounds, once released or formed during processing of olives, are distributed between the water and oil phases. Another part of the phenolics is trapped in the solid phase: the "pomace". The distribution of the released amount of the phenolics between water and oil is dependent on their solubilities in these two phases. Consequently, only a fraction of the phenolics enters the oil phase. In this way, an upper limit on the kind and amount of the phenolic compounds entering the oil phase is set. In general, the concentration of the phenolics in the olive oil ranges from 50 to 1000 μg/g of oil depending on the olive variety [4] . This amount of antioxidants in the olive oil is 1-2% of the available pool of antioxidants in the olive fruit. The rest is lost with the wastewater (approximately 53%) and the pomace (approximately 45%) depending on the extraction system [5] . Some of the phenolic compounds present in the olive oil possess antioxidant activity, thus imparting higher stability to the oil. The most important of the phenols of the olive oil, in terms of having the highest protection factor [6] , that possess antioxidant activity is the 3 , 4-dihydroxyphenylethanol (3,4-DHPEA) [6-8] . The 3,4-DHPEA is present in different oleosidic forms: the 3,4-DHPEA form, the form linked to the dialdehyde form of elenolic acid (3,4- DHPEAEDA) , and as an isomer of oleuropein aglycon (3,4-DHPEAEA) [7] . All of these three forms are degradation products of oleuropein. Oleuropein is a glu- coside that contributes to the bitterness of olives. The antioxidant activity of all three forms is different, as well as their biological activity [9] . Their antioxidant activity is also dependent on the concentration of these compounds, and more specifi- cally, it is proportional to the antioxidant concentration in the oil phase [10] . During processing for the extraction of olive oil, almost 80% of all oleuropein is degraded upon crushing the olives. In the olive paste, which is a multiphasic system, the anti- oxidants partition into the different phases thermo- dynamically according to their affinities toward these phases. The proportions of antioxidants residing in the three different phases (oil, water, and solids) depend on the relative polarities of the antioxidants, presence of surfactants, temperature, and the composition and relative amounts of the phases. A number of OMWW purification methods have been employed in recent years and these can be divided into physico-chemical and biological methods. The physicochemical methods are based on OMWW treatment with flocculants and coagulant, cryogenesis, ul- trafiltration, reverse osmosis, thermal concentration and evaporation in ponds. These methods are generally very expensive and/or unable to completely solve the problem because of the need to dispose of a sludge deriving from the process [11] . Biological methods are based on production of proteins, poly-hydroxy-b- butyrates, poly-hydroxy-alcanoates and exopolysaccha- rides, anaerobic digestion and composting [12-14] . These methods have certain clear benefits due to the potential utilization of their by-products. For economic reasons, OMWW is mainly stored in evaporation ponds, which, as mentioned previously, produce sludge. Because of the high organic load and the substantial quantity of plant nutrients (N, P, K, Ca, Mg and Fe) in OMWW sludge [15] treatment by composting to obtain organic fertilizers is, in principle, very appropriate. During composting, microorganisms degrade aerobically labile organic carbon compounds, such ^■ as proteins, ^'.amino acids and^'- -pe tides to carbon- dioxide, water, ^' mineral salts and a stable organic material containing humid-like substances [16] . Several studies have been performed on the composting of OMWW. Tomati et al . [17] found that, when OMWW was composted with chopped wheat straw and urea, a rapid increase of microorganisms and bio-reactions occurred at the beginning of the process, which led to an increase of the temperature and pH and a decrease of total organic carbon. Also, during OMWW composting with different organic wastes rich in N and lignin- cellulosic wastes, Paredes et al . [12] found that to-- tal N losses by NH₃ volatilization and N₂ fixation ac-

- tivity increased during the .bio-oxidative phase, the former remaining stable and the latter falling during maturation. Moreover, a substantial quantity of N0₃ was observed by the end of the bio-oxidative phase, however maximum values were reached only after maturation [12] . Tomati et al . [18] and Paredes et al . [19] obtained composts with a high level of humifica- tion and without phytotoxic effects by composting OMWW. However, there is a lack of data on OMWW sludge composting.- The filtration methods used in previous studies imply the use of ultrafiltration or the use of cryogenic equipment. Although good results have been reported, both ultrafiltration and cryogenesis could not be used in a large scale, in an efficient way. This can be attributed to the heaviness of the equipment, as well as to the limited efficiency of the methods for the treatment of large volumes of wastes . Consequently, there persists a need for development of new methods for the purification of olive mill waste waters, which are capable of treating large volumes in a handy and inexpensive way.

Description of the invention The present invention relates to a system of filters for use in the treatment of olive mill waste waters (OMWW) , wherein said system of filters is com- posed of a combination of sub stratums of natural products selected from a group comprising turf, sand, and sawdust, and optionally one or more filters of resins selected from the group consisting of cationic, mixed-bed, and PVPP. Such a system offers several advantages as compared to filtration systems known in the art. First of all, the system of filters is made of inexpensive physical product filters (sawdust, turf, sand) . Secondly, the system offers a considerably degree of flexibility. As the system is made up of a discrete number of filters, the number of each kind of filter in the system is easily changed. Such flexibility is required in cases of changes in the volume and/or chemical composition of the waste waters to be treated. One aspect of the present invention relates to a system of filters for use in the treatment of olive mill waste waters. By the term "olive mill waste waters" (OMWW) as used herein is meant any aqueous fluid produced during the milling and pressing of olives in any kind of olive mills, using pressing, cen- trifugation or any other type of separation methods. The system of filters may be made up by any number of filters necessary for a satisfactory purification of - a ^' specific OMWW. A person skilled in' the art will appreciate that the ^' number and the exact combination of filters will depend on the chemical and physical nature of the waste waters to be treated. According to the invention the filters is composed of a combination of sub stratums of natural products selected from the group consisting of turf, sand, and sawdust. As used herein the term "turf" is defined as the upper stratum of earth and vegetable mold, which is filled with the roots of grass and other small plants, so as to adhere and form a kind of -mat.- The term "sand"- is defined as fine particles of stone, especially- of siliceous stone,, but ■ not reduced to dust as well as comminuted stone in the form of loose grains, which are not coherent when wet. The term "sawdust" is defined as dust or small fragments of wood (or stone etc.), which for example is made by the cutting of a saw. Additionally, one or more filters of resins may be incorporated into the system of filters . By incorporation of said resins the efficacy of the system of filters is increased. Furthermore, the use of resins makes it possible to retain high additive value products, such as antioxidant biophenols, which are present in the waste waters to be treated. A subsequently recovery as the resin is regenerated is then possible. Consequently, the use of the system of filters is made more profitable. In a preferred embodiment the system of filters is made up of one turf filter, one sand filter and one sawdust filter, and optionally two filters of resins . ^•• In. another, preferred, embodiment the system of filters is made up of one turf filter, one ^' sawdust filter, and one sand filter, and optionally two filters of resins. In yet another preferred embodiment the system of filters is made up of two turf filters and one sand filter, and optionally two filters of resins. In still another preferred embodiment the system of filters is made up of two sawdust filters and one sand filter, and optionally two filters of resins . By the term "resins" as used herein is meant an ion-exchange resin made of a .high-molecular-weight polymeric material - containing several ionic-^' functional groups per molecule. In a preferred embodiment the resin is a cationic resin. As used herein the term "cationic resin" is defined as an ion-exchange resin, which has negatively charged functional groups (preferably sulfonic acid groups or carboxylic acid groups) attached, and therefore are capable of exchanging cations. An anionic resin is defined as an ion-exchange resin, which has positively charged at- tached, and therefore is capable of exchanging ani- ons . In another preferred embodiment the resin is a mixed-bed. As used herein the term "mixed-bed" is defined as a single vessel in which cationic and anionic resins are mixed together or are resins contain- ing both cationic and anionic groups. In yet another preferred embodiment the resin is PVPP. As used herein, the term "PVPP" is defined as a resin made of polyvinylpolypyrrolidone . Another aspect of the invention relates to a method for treatment of OMWW using a system of filters according to the present invention wherein said method comprises the step of: a. producing an effluent by passing the OMWW through said system of filters. In a preferred embodiment of the method, the organic filter is further burned at a temperature comprised between 1500 and 800°C, more preferred be- tween 1200 and 900°C, and even more preferred between 980 and 900°C. The produced smoke does not contain any trace of organic material (ex. dioxins) , except C0₂ and its NOx content is lower than 1%. In a further preferred embodiment the method further comprises the-, step of : b. regenerating the system of filters composed of the combination of sub stratums of natural products selected from a group comprising turf, sand, and sawdust and/or the filters of resins either simulta- neously or separately by passing on organic solvent through said part of the system of filters. In yet another preferred embodiment the method further comprises the step of: c. adding a flocculant to the effluent obtained in step a in order to eliminate colour of the effluent . The major advantages of the method according to the present invention is that it is inexpensive, it is possible to treat large volumes of waste waters, and the rate at which the waste waters are treated is very fast compared to methods known in the art . According to step b in the method of the pre- sent invention, the whole or part of the system of filters is regenerated by passing an organic solvent through the sys^'tem of filters composed of the combination of sub stratums of natural products selected from a group comprising turf, sand, and sawdust and/or the filters of resins either simultaneously or separately. It is obvious for a person skilled in the art that the choice of organic solvent will depend on the kind of substances, which are to be removed from the filters as well as the type of filter material. Examples of organic solvents include low or high weight alcohols. Methanol is the preferred organic solvent for regeneration of the resin filter, while ethanol is preferred whenever possible uses in humans are envisaged. Preferably, the resin filters are regenerated separately from the rest of the filters in order to isolate and recover the valuable antioxidant biophe- nols, which only are retained by the resin filters. All well-known methods for regenerating different kinds of resins are obvious for the skilled practitioner. Optionally, a flocculant may be added to the effluent obtained in the method of the invention in order to eliminate any colour. Many kinds of substances may attribute to the colouring of the effluent, and therefore a person skilled in the art will appreciate, that the choice of flocculant is dependent on the kind of substance or mixture of sub- stances, which are to be removed from the effluent.

Examples of flocculants include Aluminium and other absorbent salts. In yet another aspect of the present invention the effluent obtained from above-mentioned method is used for agricultural irrigation. In this way the subsequent discharge of the treated waste waters is taken care of by recycling both organic matter and nutritive elements to the soil-crop system. Still another aspect relates to a method for retention and recovery of highly valuable products, such as antioxidant biophenols, present in the OMWW by use of the system of filters according to the in- vention, wherein said method comprises the steps of: A. retention of said highly valuable products on the filters of resins by passing the OMWW through said system of filters, B. separating the filters of resins from the other filters, C. washing of the filters of resins by passing a solvent through said filters, and D. regenerating the filters of resins by passing an organic solvent through said filters and thereby recovering said highly valuable product. As mentioned above, the possibility of recovering highly valuable products makes the use of the invention more attractive and profitable. Methods of retention of chemical products on filters and the subsequent recovery by regenerating the filters are well known in the art, and therefore above-mentioned method is easily performed by a skilled person. Further characteristics and advantages of the invention are given in the following examples and the attached Figures. Figure 1 presents the purification of OMWW obtained by the method according to the present invention. The white bars indicate the purification rate in terms of the concentration of phenols, whereas the black bars indicate the acidity. Figure 2 presents a flow-chart of the method described for the production of an aqueous effluent, for use in agriculture. Numbers show the percentage of phenolics found in every stage of the purification method. Heavy arrows show the principal treatment (turf-turf-sand) . Light arrows present the alternative method of purification (turf-sand-turf) . At each stage, turf can be replaced by sawdust. Figure 3 depicts the procedure used for the second filter, leading to the isolation of biophe- nols. Numbers indicate the percentage of remaining biophenols, as compared to non-treated OMWW. The first stage filter is the one presented in Figure 2. Figure 4 depicts a possible construct of the proposed filter. The first stage filter (circles) consists of sawdust, turf, and sand, in different order, as described in the text and in Figure 2. The second stage filter consists of mixed bed, cationic or PVPP resins. At each stage, an electrochemical conductivity sensor controls the condition of each filter. A pump at the beginning of the filter series controls the flow.

Examples

Materials and chemicals The OMWW employed in the experiments was waste water from 3 phase centrifugal olive oil mill (OW) . To the construction of the filters the following materials were used: commercial sawdust for pets, iron gauge, cheesecloth, canvas sheets and sheets of as- bestos cotton, standard filter paper, sartorius filters of fibreglass lOμm and cellulose acetate Iμm, plough se_.eds of cardamom, soil and turf mix for home gardening, and as resins: Amberlite XAD 16 or XAD 4 5 (Rohm & Haas a.s 63117) or any compatible mixed bed or cationic resin, and polyvinylpolypyrrolidone PVPP (Sigma P-6755) . Furthermore, the following chemicals were used: caffeic acid (Fluka 60018) , gallic acid (Sigma G-

10 7384), methanol MeOH (Merck p. a.), isopropanol IPA (SDS p. a.), and ethyl acetate EtOAc (SDS p. a.). When performing the experiments the following instruments were used: Buchner funnel, with vacuum conical flask and electric vacuum pump, Sartorius

15 vacuum filtration system with electric vacuum pump, Laboratory centrifugal, Electric roller table, Electric shaking table, and Double beam UV-Vis spectro- photometer .

20 Example 1. Description of the filters Treatment of OMWW in view of their purification The main objective of this part of the invention was the direct purification of OMWW, in view of the direct use of the effluent, for agricultural pur- 25 poses. In this respect, OMWW were treated with a number of substances, in order to eliminate the major part of biophenols. The treatments and results are presented in the following table. We present the combination of two filtrations over turf, combined with

30 an additional sand filtration, in order to improve the pH of the final effluent (Turf-Turf-Sand TTS, and Turf-Sand-Turf TST) . At each procedure, turf can be replaced by sawdust, with similar results. The results are shown in table 1.

Table 1.

*Toxicity was assayed by cardamom seed growing, as compared to seeds cultured in the presence of water

As shown, although the addition of sand, as a second filter improves the - purification, .the final pH of the effluent is lower. Nevertheless, the above procedure (TST turf-sand-turf) does not present a greater toxicity for cardamom seed growing, as compared to the procedure TTS. Similar results, with comparable yields have been obtained by the replace- ment of turf by sawdust. In this respect, the above- mentioned filter could be replaced by one containing Turf-Sawdust-Sand in any combination. Figure 1 presents the different combinations of sand, turf and sawdust, together with the pH variations obtained. As presented, in the above procedure, the addition of a third component (sawdust) does not induce a better yield either in phenolics or in pH. For the above purpose, the purification of OMWW can be achieved as presented in the flow diagram presented in Figure 2. Example 2. Treatment of OMWW in view of the purification of biophenols Treatment of the wastewater with sawdμst and resins The sawdust was sieved through iron gauge and so separated to thin sawdust (SD) and saw chippings (SC) . 800mL of OMWW was mixed with 20g SC (20/1 mixing ratio) in 1L beaker and manually stirred with spatula for 15min. The mix was then sieved through the holes of a Buchner funnel under vacuum and filtered under vacuum through cheesecloth on a Buchner funnel. The first filtrate Fa was mixed with SD, in 20/1 mixing ratio, and stirred manually with spatula for 15 min. The mixture was filtered under vacuum through ^' asbestos cotton. The process- was repeated once more with second filtrate Fb . The filtrate Fc was filtered under vacuum through canvas sheets and then mixed with XAD 16, in 10/1 mixing ratio and stir mixed on a magnetic stirrer 15 min. The mixture was filtered under vacuum through asbestos cotton. The process was repeated with the forth filtrate Fd for 3 more times.

Table 2. Scheme for treatment of the waste water with saw- dust and resins .

Tests of phytotoxicity 50mL of treated OW were poured into lOg of soil and turf mix in a glass beaker. After 2 days the excess water was poured off and 30 seeds of cardamom were ploughed, half deep into the wet soil. The bea- ker was covered with a bigger beaker and kept indoors next to a window. After 2 days the number of seeds with sprouts was counted. A reference culture was prepared with 50mL tap water instead of OW. The final effluent resulted in a 70% germination of the seeds, and can be used for agricultural purposes.

Retention and recovery of phenolics from different resins 1 L of OMWW was filtered under vacuum through cheesecloth on a Buchner funnel. The filtrate was filtered under vacuum with a Sartorius funnel through filters of fibreglass filters lOμm and then filters of cellulose acetate lμm. The final filtrate was mixed with XAD16 resin at different mixing ratios (see the following tables) in roll tubes with screw caps. The tubes were mixed vigorously in vortex and then roll mixed on an electric roller table for 18hrs. The tubes were centrifuged at 3000 rpm for 10 minutes. The supernatant was removed with Pasteur pipettes for analysis of total polyphenols. The pre- cipitate was mixed with MeOH at variable mixing ratios. The content of the tubes was mixed vigorously in vortex and then roll mixed on an electric roller table for 18hrs. The tubes were centrifuged at 3000 rpm for 10 minutes. The supernatant was removed with Pasteur pipettes for analysis of total polyphenols. Solvent residues were evaporated from the tubes with the precipitated resin under nitrogen stream. The tubes with the resin were reused with new amounts of filtrated OMWW and the process was repeated as above. Table 3. Retention and recovery of total biophenols, after repeated absorption by XAD16

In view of the above results, a flow chart of OMWW purification with a combination of filters is presented in Figure 3. In this method, the final effluent can be directly used for agricultural purposes, and the polyphenols can be extracted from the resins. A possible construction for the production of a filter in use in olive mills is presented in Figure 4. At a later, stage, in needed, a flocculation method can be applied, in order to eliminate the light yellow colour, and produce a more transparent product . A number of commercially available floccu- lants have been assayed with equally good results.

References 1. Saviozzi A, Riffaldi R, Levi-Minzi R, Scag- nozzi A, G: Decomposition of vegetation-water sludge in soil. Bioresour. Technol . 1993, 44:223-228. 2. Sciancalepore V, De Stefano G, Piacquadio P, Sciancalepore R: Compostaggio in ambiente protetto del residuo della lavorazione delle olive con impi- anti ad estrazione bifasica. Ing. Ambientale 1995, 24:627-631. 3. (7), Pannelli G, Servili M, Baldioli M, Montedoro G: Changes in the phenolic and pectic substances in olive fruit and oil as a function of ripening, cultivar and extraction technology. OLEA 1991, 21:64. 4. (8), Montedoro G, Servili M, Baldioli M, Miniati E: Simple and hydrolyzable phenolic compounds in virgin olive oil. 1. Their extraction, separation and quantitative and semiquantitative evaluation by HPLC. J. Agric. Food Che . 1992, 40:1571-1576. 5. (9), Union E: Improvement of olive oil quality by biotechnological means; Final Technical Report, Project AIR3-CT93-1355. In: Book Improvement of olive oil quali ty by biotechnological means; Final Technical Report,- Project , AIR3 -CT93 -1355 (Editor ed. eds.) . City; 2000. 6. (10), Papadopoulos G, Boskou D: Antioxidant effect of natural phenols on olive oil. J^". Am. Chem . Soc . 1991, 68:669-671. 7. (12), Montedoro G, Servili M, Baldioli M, Miniati E, Macchioni A: Simple and hydrolyzable compounds in virgin olive oil. 3. Spectroscopic characterizations of the secoiridoid derivatives. J. Agric . Food Chem. 1993, 41:2228-2234. 8. (11), Kochhar S, Rossel J: In: Food Antioxi - dants Edited by Hudson B. pp. 19-53. London: Elsevier Applied Science; 1990: 19-53. 9. Tuck KL, Hayball PJ: Major phenolic compounds in olive oil: metabolism and health effects. J^" Nutr Biochem 2002, 13:636-644. 10. (14), Ranalli A, Angerosa F: Integral cen- trifuges for olive oil extraction. The quality characteristics of products. J^". Am. Oil Chem. Soc . 1996, 73:417-422. 11. Martinez Nieto L, Garrido Hoyos S: El. alpechin. Un problema medioambiental en vias de solucion (I). Quibal 1994, 41:755-765. 12. Paredes C, Roig A, Bernal M, Sanchez- Monedero M, Cegarra J: Evolution of organic matter and nitrogen during co-composting of olive mill wastewater with solid organic wastes. Biol . Fert . Soils 2000, 32:222-227. 13. Ramos-Cormenzana A, Monteoliva-Sanchez M, Lopez M: Bioremedation of alpechin. Int . Biodeter. Biodegr. 1995, 35:249-268. 14. Vlyssides A, Bouranis D, Loizidou M, Karvouni G: Study of a demonstration plant for the co-composting of olive-oilprocessing wastewater and solid residue. Bioresource Technol . 1996, 56:187-193. 15. Paredes C, Cegarra J, Roig A, Sanchez- Monedero M, Bernal M: Characterization of olive mill wastewater (alpechin) and its sludge for agricultural purposes. Bioresource Technol . 1999, 67:111-115. 16. Senesi N: Composted materials as organic fertilizers. Sci . Total Environ . 1989, 81/82:521-542. 17. Tomati U, Galli E, Pasetti L, Volterra E: Bioremediation of olive-mill wastewaters by composting. Waste Manage . Res . 1995, 13:509-518. 18. Tomati U, Galli E, Pasetti L, Volterra E: Olive-mill wastewater bioremediation: Evolution of a composting process and agronomic value of the end product. In: The Science of Composting Edited by Papi T. pp. 637-647. Glasgow: Blackie Academic and Professional; 1996: 637-647. 19. Paredes C, Bernal M, Roig A, Cegarra J: Effects of olive mill wastewater addition in composting of agroindustrial and urban wastes. Biodegradation 2001, 12:225-234.

Claims

P A T E N T C L A I M S 1. A system of filters for use in the treatment of olive mill waste waters (OMWW) , wherein said system of filters is composed of a combination of sub stratums of natural products selected from the group consisting of turf, sand, and sawdust, and optionally one or more filters of resins selected from the group consisting of cationic, mixed-bed, and PVPP resins. 2. A system of filters according to claim 1, wherein said system of filters comprises one turf filter, one sand filter and one sawdust filter. 3. A system of filters according to claim 1, wherein said system of filters comprises one turf filter, one sawdust filter, and one sand filter. 4. A system of filters according to claim 1, wherein said system of filters comprises two turf filters and one sand filter. 5. A system of filters according to claim 1, wherein said system of filters comprises two sawdust filters and one sand filter. 6. A system of filters according to any of the claims 2 to 5, wherein said system of filters additionally comprises two filters of resins. 7. A method for the treatment of OMWW using a system of filters according to any of the claims 1 to

6, wherein said method comprises the step of: a. producing an effluent by passing the OMWW through said system of filters. 8. A method according to claim 7, wherein said method further comprises the step of: b. regenerating the system of filters composed of the combination of sub stratums of natural products selected from a group comprising turf, sand, and sawdust and/or the filters of resins either simultaneously or consecutively by passing an organic solvent .through- said parts of .the system of filters. 9. A method according to claim 7 or 8 , wherein said method further comprises the step of: c. adding a flocculant to the effluent obtained in step a in order to eliminate colour of the effluent . 10. Use of the effluent obtainable by the method for treatment of OMWW according to any of the claims 7 to 9 for agricultural irrigation. 11. Method for retention and recovery of highly valuable products, such as antioxidant biophenols, present in the OMWW by use of the system of filters according to any of ^• t-he claims..1 to 6, wherein said method comprises the step^'s of: ' A. retention of said highly valuable products on the filters of resins by passing the OMWW through said system of filters, B. separating the filters of resins from the other filters, C. washing of the filters of resins by passing a solvent through said filters, and D. regenerating the filters of resins by pass- ing an organic solvent through said filters and thereby recovering said highly valuable product.