WO2009101455A1

WO2009101455A1 - Physicochemical method of processing liquid and semisolid wastes of olive mills using ozone (o3)

Info

Publication number: WO2009101455A1
Application number: PCT/GR2009/000011
Authority: WO
Inventors: Pantelis Xynogalas
Original assignee: Pantelis Xynogalas
Priority date: 2008-02-11
Filing date: 2009-02-10
Publication date: 2009-08-20
Also published as: GR1006296B

Abstract

Physicochemical methods and oxidative process used to solve the problem of pollution of olive mills wastewater. The application of the suggested technology is based on ozone transmission through liquid waste of olive mills by combination with coagulated action of a minimal ferrous sulphate quantity. Using this method detoxification of olive mill wastes is guaranteed with simultaneous decrease of pollution load about 95%. Under acidic conditions and the organic substrate presence and a small ferrous sulphate quantity the ozone is decomposed as follows: O3 + H2O +Fe2+ → O2 + Fe3+ +OH- + OH+ The hydroxyl radicals are very effective and they attack the organic compounds RH in a minimal time and non-selectively resulting organic radicals. The obtained oxygen reacts with them and thus the organic material decomposition takes place the oxidized liquid and wastes are subjected a further ozonization and a biological process in order to be suitable for fertirrigation. The obtained chemical sludge from oxidation and neutralization reactors with the produced biological by aerobic and anaerobic processes, are syn-composted with olive leaves, olive stone and other agricultural wastes on dried up bed in order to produce a fertiliser of the best quality.

Description

Physicochemical method of processing liquid and semisolid wastes of olive mills using ozone (O₃)

As it is known the olive tree is the most significant tree like cultivation of the Mediterranean countries. There are the 98% of the olive trees of the world. Although the important role which this specific agricultural activity plays in reference to our national economy, there are significant problems deriving from the olive reaming process, because of the large amount wastes.

More specifically in Greece 1,5 million tons of olive mill wastes are produced yearly. They are derived from liquid fraction of olive sap and from water which is added during the phases of washing, kneading and from olive oil separation. The wastes have a characteristic strong odor, acidic PH, high buffer capacity and surface tension. Further more they contain a rich organic substances amount, which are classified as follows:

Decomposed substances such as, sugars and organic acids. Biodegradable polymers (proteins) Compounds, which are decomposed difficultly, like fatty substances and phenols. It has also been reported, that the phenolic content attributes to the phytotoxicity and the wastes microbial properties. In combination with the high values that have been measured for biochemical oxygen demand (BOD) and chemical oxygen demand (COD), they have very strong toxic action. The essential properties of the waste depend on the production process and the quantity of the added water. They range usually in the following values: PH = 3 - 6, BOD = 20-60g/L and COD = 90 - 170g/L.

Physicochemical methods like filtration, centrifugation evaporation, coagulation and precipitation, inverse osmosis and superfiltering used to solue the problem of pollution. Recently oxidation with oxygen under high pressure, oxidation with electrolysis and finally the Fenton oxidative process hydrogen peroxide (H₂O₂) and ferrous sulfate (FeSO4), which is a method which combines chemical oxidation with organic compounds coagulation, were used.

Later combined methods predominated in order to take Commercial products from the treatment of the wastes like compost and proteins for animal feed, thus the applied techniques to be economically feasible. Simultaneously biological process of cleaning and toxic substances decomposition used in order to produce byproducts of high added value like compost and fertilizers. The last years limited number of the two phases olive mill (ecological oil - plants) has been established and work. Using this specific technology the volume of wastes decreases as well as the amount of using water during the olive oil production. However the polluting load shows an increase on its consentration per volume unit. Also it is necessary a further pulp treatment in specific oil-plants from where oil, olive stone and a large amount of semisolid waste having a moisture content of about 70% are obtained. This method is nothing but transferring the liquid wastes problem to solid wastes. Besides it has been demonstrated, that the oil has been produced by the two phases process, has higher acidity and lower quality than the oil comes from the traditional way production. Substantially the oil plant conversion from three phases to two phases (repasso method) not only does not solve the environmental problem, but also demands the industrialization of oil tree cultivation at the expense of the olive oil quality. At the present invention it is proposed a method of processing liquid wastes from olive mills using O₃, which has been produced from specific and economical devices. As it is known the ozone when is reacting with water has the ability to detoxify it about 100%. Ozone oxidies the phenole's byproducts, the detergents, the industrial chemical wastes and the aromatic compounds, which have intense odor without living toxic wastes. The application of this prototype technology, which is described at present, is based on ozone transmission through liquid waste from olive mills by combination with coagulated action of a minimal ferrous sulfate amount. Using this method is detoxification guaranteed from olive mill wastes with simultaneous decrease of pollution load about 95%. The results of the above are: 1) Water production suitable for fertirrigation 2) The usage of the detoxified wastes to produce a fertilizer of the best quality

The application of the above proposed technology is also more economical and effective than the chemical oxidation by Fenton's reagents and furthermore maintains the traditional way of olive oil production, which qualifies to be of highest quality. The above method is described to block diagram (figure 1).

The liquid waste is transported through the perpendicular pump suitable for sludge (1) into a stainless oxidation tank (2). The ferrous sulfate solution is prepared into a small volume stainless tank (3), and it is transferred through a system of metering (4) into the oxidation tank. At the same time ozone, which is produced by appropriate generator (5), is transmitted into oxidation reactor. Organic and chemical sludge (6) are precipitated on the oxidation tank basis and carried out in order to be used as fertilizer. Finally the obtained water is carried out by physical flow into a concrete storage tank (7). The no toxic water is suitable for fertirrigation. All the above used tanks must be made of stainless steel and the pipings made of PVC. In some special cases we must use silicones.

As it has been mentioned already the waste PH ranges between the limits 4 and 6. Thus under acidic conditions, the presence of organic substrate and a small amount of ferrous sulfate, ozone is decomposed rapidly to oxygen (O₂) by simultaneous hydroxy radicals (OH^*) production.

O₃ + H₂O +Fe²⁺ → O₂ + Fe³⁺ + OH^" + OH^' (1) Unless most of radicals have no electric charge, are very effective. For example they can remove a hydrogen atom from another molecule resulting to a new radical. Alternatively a radical can be added to an alkene removing an electron from double bond C-C creating a new radical. Based on the above the hydroxy radicals attack the organic compounds RH in a minimal time and no selectively, according to the following reaction.

OH^* +RH → H₂O + R^* (2) The obtained oxygen (O₂) from reaction (1) reacts with the organic radical (R^*) and thus the breaking down of the organic materials has been succeeded.

O₂ + R^* → O₂R^* (3) The Fe³⁺ ions produced react with the hydroxyl ions (OH^") to form complexes. [Fe(H₂O)₆]³⁺ + H₂O → [Fe(H₂O)₅OH]²⁺ + H₃O⁺ (4)

[Fe(H₂O)₅OH]²⁺ + H₂O → [Fe(H₂O)₄(OH)₂]⁺ + H₃O⁺ (5)

Thus we notice that in the PH range from 4 to 6 with a series of hydrolytic reactions, complexes of Fe³⁺ and hydroxyl are formed. As the charge of the complexes is decreasing due to the increase of the number of hydroxyl ions, the repulsion between ions is reduced and their tendency to polymerize is increased. By this way some indissoluble colloidal polymers of ferric oxide hydrate are produced which precipitate finally. Hence suspended particles as well as organic molecules are entrained by the accretions and precipitate. This results to a decrease of the waste's COD number demonstrating the coagulational action of ferrous sulfate. It should be noted, that where it is necessary a small amount of hydrogen hyperoxide (H₂O₂) must be used with ozone simultaneously.

This reacts with Fe²⁺ ions and move hydroxy radicals (OH) are produced, indispensable during the whole oxidation process. Fe²⁺ + H₂O₂ → Fe³⁺ + OH^" + OH^* (6)

The ozone and ferrous sulfate quantities are used at the present procedure depend on volume and polluted load of oil-plant liquid wastes. According to another embodiment, besides the initial which is general, the present invention is described as follows (figure 2):

A tank made of stainless material (2) is used for liquid waste oxidation, which is transferred through suitable pump (1), where is a stirring system (3) and the appropriate system (4) for the atmospheric air supplying into the tank. The air assists the stirring, providing an extra oxygen amount. Ozone generator (5) is supplied by a manufacture industry or could be manufactured locally. The ozone flow will be ranged between 50g/h and 2.5 kg/h. accordingly to waste COD. Thus O₂ and OH will mainly be obtained and other oxidative such as O₂, H₂O₂, active oxygen. Dosimetric pump (6) will supply the system with FeS04 solution, which is prepared into a small tank (7) with a suitable stirring system. It is desirable, that the quantity of Fe²⁺ be as small as possible, so Fe²⁺ ions don't bind a large number of OH. This ranges from 3 kg to 7 kg/m³ of liquid waste. This should be remained into this reactor almost an hour. The waste is coming out through the appropriate pump (9) and since it is filtered though bagfilter (10) or cartridge or sand filter leads to another stainless tank (11), where it is stirred by a stirring system (12) with Ca(OH)₂ or NaOH according to follow reaction:

Ca(OH)₂ +FeSO4.7H2O → CaSO₄ + Fe(OH)₂ +7H₂O (7)

There after it takes place the oxidation reaction, because of the dissolved oxygen:

4Fe(OH)₂ +O₂ + 2H₂O «→ 4Fe(OH)₃J (8)

Further addition of a calcium hydroxide small quantity gives:

Fe₂(SO₄)₃ + 3Ca(OH)₂ «→ 3CaSO₄ +2Fe(OH)₃J, (9) The total obtained insoluble precipitate Fe(OH)₃ entrains the suspended colloidal particles. At the same time extra ozone is piped in order to achieve a more decrease of waste polluting load. As it is known, under acid conditions, the Ca(OH)₂ or NaOH or KOH addition extents the ozone life time and consequently its efficacy time. Also, the above addition decreases the carbonate and the acidic carbonate ions, which deactivate a large amount of radical OH^*.

Then the liquid is carried out the neutralization tank with suitable pump (13) and it is filtered through active carbon filter (14). After that it undergoes aerobic or anaerobic treatment (15) for nitration The final obtained water goes into a concrete storage tank (16) and it is processed with ozone it has an almost zero polluting load. Thus, it is suitable for many usages, which relate to agricultural economy and not only. The chemical sludge (17) are pumped by the appropriate pump (18) from oxidation and neutralization tanks and with biological are syncomposted with olive leaves, olive stone and other agricultural wastes on a drier bed (19). At the same time they should be soaked by the ozonized liquid waste, then the final product should be a fertilizer of very high quality. It is detectable that with ozone use the physicochemical process becomes more effective in reference with Fenton system. That loses its oxidative action since PH decreases. Also for a signifying increasing of liquid waste COD, the H₂O₂ and FeSO₄ quantities must be decreased.

However this is unprofitable but also ineffective, since H₂O₂ is unstable and deactivates a large number of OH^". Thus large quantities of ions of solute iron remain in the wastes thus it should be become inimical to the environment. As it is known ozone is transformed to oxygen, so its most effective action in reference with hyperoxide is showed at the follow reaction

Fe²⁺+ O₂ → Fe³⁺+ 0_2→ (10)

Where O_2→ is the hyperoxide radical, which has strong oxidative action. Finally, must be taken into account the oxidation time, which increases when temperature decreases by proportional way. The proposed method could be applied into the two phases olive mills, since in this case liquid wastes are obtained. Specifically, during the moist husk resolution, the wastewater requires further physicochemical treatment and biorectification.

The described invention about the liquid and semisolid wastes of oil plants when it is applied, ensues the following advantages:

1. The waste (ratio COD/BOD) toxicity decreases because of the solute oxygen large quantity. Thus, the further aerobic or anaerobic digestion should be more effective. The obtained water after ozonization becomes the highest quality of fertirrigation. 2. Because of ozone dissociates to water the wastes aren't extra charged according to toxicity, since the demanded FeSO₄ quantities are less than in reference with Fenton process. 3. It achieves the maximum decrease of COD, of the fatty organic compounds, of phenolic compounds, of the dyes and of the turbidity. 4. The present method because of its simplicity is useful and economical.

Furthermore: a) The ozone generator either is purchased once or it is manufactured and installed locally. Thus is used and for other procedures apart from wastewater treatment from olive mills, which are related to agricultural economy generally, like it happens in advanced European countries and U.S.A. b) The organic substance produced after its syn-composting with olive stone, leaves and other woody byproducts forms a fertilizer of very high quality useful for every oil- plant and in any case commercialized.

Below is given an example of practice of the suggested method and is does not limit the present invention in regard to anything. Two tons (2 m³ or 2000 kg) of wastes is placed with continuous stirring in a stainless container of 5 m³ capacity. The waste's composition is: COD = 160 g/L, BOD₅ = 35 g/L, SS = 90 g/L, total phenolic compounds = 15 g/L and PH = 4.2. To this container 15 kg of solid FeSO₄ VH₂O as solution of 30% w/v are added, which has prepared into of 70 L tank with a stirring system. This addition takes place by a docimetric pump with a flow rate of 50 L/h.

Ozone generator of the OZONIA manufacturer with maximum flow rate 1.24 kg/h has been already started up. Thereafter 2 L of a 50% solution Of H₂O₂ is added, while correspondingly air is transmitted at a rate of 16 m³/h.The air like ozone aims at the mixture's stirring. This remains in the oxidation reactor about 1 hour and after diluting 1 : 1 with purified water is filtered through a bag filter.

The filtration result is transferred to the suitable tank with stirring system, where is neutralized with calcium hydroxide (Ca(OH)₂) (PH = 8.2) and at the same time is ozonated. Then it is filtered through a carbon active filter. The filtrate obtained has the following characteristics:

COD = 1.2 g/L, BOD₅ = 0.95 g/L,

SS = 0.4 g/L and total phenolic compounds = 0.07 g/L.

This filtrate has been processed with an aerobic or anaerobic digestion and more ozonization should be of almost zero polluting load. The mass of chemical and organic sludge obtained from whole above procedure is the 1/3 of the initial wastewater mass approximately and it is disposed for composting.

Claims

1) Method of processing the liquid and semisolid wastes of olive mills using ozone (O₃) and reducers.

2) Method of processing the liquid and semisolid wastes of olive mills by combination of ozone, hydrogen peroxide, air and ferrous sulfate into a suitable stirring reactor.

O₃ + H₂O + F³⁺ → O₂ +Fe³⁺ + OH^" + OH'

Fe²⁺ + H₂O₂ → Fe³⁺ +OH^' + OH^*

3) Method of processing the liquid wastes of olive mills according to claim 1 characterized in that the ozone generator either is supplied from industrial manufacture or it is manufactured and installed locally.

4) Method of processing the liquid wastes of olive mills characterized in that the wastewater is filtered and since it would be subjected to neutralizing with an alkaline solution, it is separated to sludge and liquid filtrate. 5) Method of processing the liquid wastes of olive mills according to claim 2 characterized in that per m³ of liquid wastes, from 0.3 kg to 15 kg of ferrous cations, from 50 kg/h to 25 kg/h ozone supplying and from 0.2 kg to 15 kg H₂O₂ (50%) are added.

6) Method of processing the liquid wastes of olive mills, according to claim 1 , 2, 3, 4 characterized in that the filtration should be taken place through bag filter, cartridge, sandfilter, active carbon or through filtration bed formed from olive stone.

7) Method of processing the liquid wastes of olive mills according to any preceding claim, characterized in that the liquid filtrate is subjected to further ozonization into neutralizing tank.

8) Method of processing the liquid wastes of olive mills according to any preceding claim, characterized in that the final filtrate should be subjected aerobic or anaerobic digestion and further ozonization.

9) Method of processing of the liquid wastes of olive mills according to any preceding claim, characterized in that the obtained chemical sludge from oxidation and neutralization reactors with biological those are syn- composted with olive leaves, olive stone and other agricultural wastes on dried up bed. At the same time these are soaked by the ozonized liquid waste and further more nutritive substances are added in order to fertilizer production 10) Method of processing of the liquid wastes of olive mills according to any preceding claim characterized in that this should be applied to anybody sporadic oil plants and as well as into cooperative farms of wastewater treatment of oil- plants with simultaneous or not fertilizer's production.