WO2005082176A1

WO2005082176A1 - Method and apparatus for washing and disenfecting root crop

Info

Publication number: WO2005082176A1
Application number: PCT/FI2005/000109
Authority: WO
Inventors: Eero PISILÄ; Heikki Ahonen
Original assignee: Pohjoisen Kantaperuna Oy
Priority date: 2004-02-23
Filing date: 2005-02-22
Publication date: 2005-09-09
Also published as: FI20040279A; FI20040279A0

Abstract

A method and an apparatus for washing and disinfecting root crop. According to the method, the root crop is washed with an aqueous washing liquid, which, according to the present invention, is prepared by electrolysis of chloride salt to produce hypochlorite and possibly chlorates, immediately before the washing liquid is used. Solid impurities are separated from the used washing liquid and the purified washing liquid is recovered and recirculated to produce hypochlorite and chlorate. With the help of the present invention, the creation of environment-loading waste can be avoided. The soil can be recovered and, after washing, used for growing potatoes, and the salt solution is returned to the closed washing system and continuously recirculated in the system.

Description

Method and apparatus for washing and disinfecting root crop

The present invention relates to a method for washing and disinfecting root crop, according to the preamble of claim 1.

In a method such as this, the root crop is washed with an aqueous solution containing chemicals.

The present invention also relates to an apparatus for washing and disinfecting the root crop, according to the preamble of claim 11.

Nowadays, potatoes and other root crop are washed by request of both customers and stores because that makes the root crop cleaner for customers to handle. In addition, it is even more important to wash and disinfect seed potatoes that are to be sold because that avoids the spread of plant diseases to customers' and one's own potato growing areas.

Potatoes and seeds have been protected against mould diseases, among others, in the way described in US patent publication 6,482,770. According to that publication, saponides, which are toxic glycosides derived from herb extracts, are used for this purpose. These glycosides have been employed by, for example, the native people of South America for catching fish by poisoning them.

US patent 5,962,510 describes how, for instance, by mixing a carboxy-methyl cellulose solution and table salt in natamycin, fungal diseases of potatoes can be prevented.

US patent 5,169,866 describes how micro-organisms in seed potatoes can be controlled by using bromine compounds, especially 2,2-dibromo-3-nitrilopropionamide. The potatoes are sprayed with the said compound in a closed storage room.

The Bulletin of Environmental Contamination and Toxicology (1976) 16(4), 38391 describes how the water used for washing seed potatoes is treated with the mercury compound (MeOCH₂CH₂HgCl) before it is emptied into the drain. Nowadays, for environmental reasons a procedure such as this would not be permitted.

The publication Pestcydy (Warsaw, 1980, 1-2, 64-9 describes how seed potatoes were treated with chloroamphenicol (CA-number 56-75-7) and beno yl (CA-number 17804-35-2) and that the procedure was effective against all fungal diseases. The problem was, however, the use of those seed potatoes, which were removed during sorting and which were very poisonous to pigs, for example.

US patent 5,698,200 demonstrates how extract of malted grain can be used to treat, among other things, potatoes, and to control bacteria such as the Pseudomonas, Ervinia, Agroi, Xanthomonas and Calvi bacteria. It has been known for a long time that when plants germinate, antibiotics comparable to those in mycocelial filaments are formed, and that these antibiotics are poisonous to bacteria but not to fungi. Unfortunately, antibiotic extracts of malted grain are expensive and are limited as preservatives.

According to US patent 4,795,705, genetic manipulation gives potatoes protection against plant diseases.

A Chinese study (Journal of Agricultural University of Hebei, Apr. 2001) describes how "late carbon-fungus" in seed potatoes can be avoided by, for example, washing the potatoes carefully and harvesting the seed potatoes earlier than usual, as well as by planting the seed potatoes deeper than 15cm in the ground.

An Internet article (www.gecities.com/CapeCanaveral/Lab9965/seed-sterilization) presents a method of sterilisation of the seeds of orchids, in which the seeds are washed with water containing a surface-active agent called Triton X-100, (octyl phenol ethoxylate). After washing, they are submerged in 70-95% ethanol and finally treated for 20 minutes with a 20% sodium hypochlorite, which contains 0.1% of the surface-active agent Triton X-100.

The washing and sterilising of seeds, described above, does not present the same problems as occur with potatoes and other root crop, which have a sensitive and thin skin.

The Thai Farmers Research Center Company Ltd published an article in 1996, which reveals that potassium chlorate, when used together with other fertilizers, speeds up growth and stimulate fast ripening of the harvest. However, the article states that the use of chlorates is dangerous because they might explode, especially when used together with ammonium nitrate or urea fertilizers.

In The Netherlands, potatoes are washed and sterilised (Novu Mashines) using water treated with ozone. Ozone can be characterised as a "quick-oxidant", which oxidizes organic material in precisely those places where the molecules touch each other, and subsequently the ozone disintegrates without leaving any secondary sterilisation. The British Potato Council states that the concentration of the ozone, which is used to treat potatoes, should be at least lOmg/litre, whereby the equilibrium concentration in air would be 2.2mg/m³. This already presents a safety hazard to people working in those conditions.

In research on the ozonization of drinking water, it has been found that the organic material broken down by the ozone provides even more biologically suitable nutrition for microbes than before (Albidress & al, Ozone Science & Engineering 17:283-295). Although ozone is effective in protecting against viruses and protozoans such as the Giardia and the

Crypto sporodium species, when inhaled it is very poisonous to human beings and its solubility in water is not adequate. Moreover, the production of ozone from air always produces nitrogen oxides and requires quite a lot of electric energy (approximately 45- 50kWh/kg O₃).

Evidently, the disinfecting of seed potatoes is difficult because it is difficult to treat the waste and the gases in an environmentally friendly manner, the washing waters are toxic and toxic substances remain in the washed soil, which is not permitted at least in organic cultivation. Many known solutions, wherein foodstuff is sterilised, do not assort to e.g. treatment of seed potatoes (or corresponding planted tubers and bulbs) because they would never again germinate after the treatment. The purpose of the present invention is to eliminate the disadvantages associated with known technology, and to generate a novel solution for the washing and disinfecting root crop, in particular potatoes.

The present invention is based on the idea that the root crop is washed using an effective and non-toxic method in which water, containing hypochlorite and chlorates produced by electrolysis, is used, after which the potatoes are dried in a current of air. The soil, which has settled out of the washing water and has been recovered in the washing, is filtered and reused. According to the invention, the washing chemicals are prepared in conjunction with the washing process, immediately before they are used.

The present invention also generates equipment that uses an aqueous washing liquid for washing root crop. Equipment like this contains a washing site, which is equipped with a spraying device for washing the root crop, which are to be treated, and with a water-collecting device for collecting the washing liquid. In addition, the equipment contains an electrolytic cell, in which hypochlorite is prepared from a corresponding salt solution, as well as the utensils for leading the washing fluid from the electrolytic cell to the spraying device and, correspondingly, the utensils for leading the used washing liquid from the water-collecting device to the electrolytic cell.

More specifically, the method according to the present invention is characterized by what is stated in the characterizing part of claim 1.

The apparatus according to the present invention in turn is characterized by what is stated in the characterizing part of claim 11.

Considerable advantages can be achieved with the present invention. By using a solution according to the invention, hazards and problems associated with toxic substances, which exist in known technology, can be avoided. Moreover, according to the invention it is possible to regulate the sterilisation effect by changing the amount of the chemicals. An obvious advantage of the present invention is that the invention can generate sterile soil suitable for planting seed potatoes. Nor does the washing method generate any waste, which would load the environment, since the soil is settled, filtered and, after having been washed in the filter, used as sterile soil for growing potatoes. The salt solution is brought back into the closed washing system and continuously recycled there.

In the following, the present invention will be examined in more detail with the help of the attached drawings.

Figure 1 is a basic drawing of the apparatus according to the present invention, explaining how to wash and disinfect root crop, especially potatoes.

Figure 2 describes a detail of a conveyor belt according to the present invention, Figure 2a as a side-view, Figure 2b as a top-view and Figure 2c as a cross section.

The following numbers are used in the figures:

1 spraying device

2 drying unit

3 body

4 settling container

5 container for washing fluid

6 electrolysis unit

7 valve

8 valve

9 sludge removal

10 valve

1 1 valve

12 pump

13 hydrogen exhaust pipe

14 valve

15 roller track In the following, the present invention will be examined in more detail, using the washing of potatoes as an example. It should be pointed out that the invention also is suitable for treatment of other root crop, such as carrots, beetroots, sugar beets and turnips, as well as onions (both eatable onions and flower bulbs) and seeds, as described at the end the special part of the explanation. Preferably, the invention is applied to seed potatoes, onions and corresponding plan-able bulbs and onions.

According to the invention, the potatoes are treated at the washing site, which is equipped with a spraying device 1 designed to direct the washing liquid onto the potato. At the washing site, the potatoes are washed with water containing hypochlorite and possibly small amounts of chlorates. Most suitably, the washing water contains also a surface-active agent. The hypochlorite and chlorate have been prepared in situ from a chloride-bearing aqueous solution by electrolysis in the hypochlorite unit 6.

After the washing, the potatoes are dried using the drying devices 2.

The washing liquid is prepared in the electrolytic cell 6. If necessary, chemicals can be added to it in the container 5. An aqueous washing liquid, which is especially suitable, contains sodium or potassium hypochlorite, prepared electrolytically in situ from a salt solution, and small amounts of chlorates, as well as approximately 0.001 -5% per weight, most suitably approximately 0.01-0.5% per weight, of a surface-active agent, such as a substance, which is poorly oxidizable and which contains alcohol or ether groups. Examples of such substances are isopropyl alcohol, pine soap, octyl phenol ethoxylate and corresponding products, which cannot be oxidized by the influence of hypochlorite or chlorate.

The amounts of hypochlorite and chlorate in the washing water must be adequate to generate a disinfecting effect. This means that the solution contains more preferably at least lOOppm, preferably at least 200ppm and most suitably approximately 200-500ppm of hypochlorite. To generate this concentration of chlorite, the salt content of the salt solution is at least lg litre, preferably at least 2g/litre, most suitably approximately 3-10g/litre of water. The washing water is recovered in the container 4, the soil is allowed to settle and is then removed 9, the cleared water is recirculated to the electrolytic cell 6 and from there as a washing liquid to the washing stage.

In the method according to our invention, the electrolytic compartment is preferably undivided and the salt (NaCl, NaOCl, Na₂ClO₃) is most suitably left on the surface of the seed potatoes, or other vegetables that are later to be planted, by drying them in a stream of air. In this way, a long-term effect with a fast delivery cycle is provided that does not harm germination.

The washing liquid is prepared "just prior" to being used, which means that the washing liquid is being used before the cooking chemicals have been significantly disintegrated into its components, according to the formula below. It is also possible to prepare some washing liquid for storage in small intermediate reserve, before it is pumped into the washing. In that case, the storage time is too short for the chemicals to disintegrate. Typically, the washing liquid contains at least 50 molar per cent of chemicals prepared in the electrolytic cell, and the washing liquid is being used either directly after its preparation or no later than 60 minutes after its preparation.

According to the present invention, the potatoes are washed with a water spray preferably from above downwards. The potatoes are washed on a horizontal conveyor belt, which is preferably made of a perforated rubber net. A track like this is shown in Figure 2. The potatoes are made to move along the roller track in one layer by lifting the rubber net in advancing peristaltic cycles. The hauling track can also be made of some suitable plastic material. Instead of the roller track, different belt conveyors with a fluid-permeable belt can also be used, such as net-like belts coated with plastic or rubber.

The washing station has water-collecting equipment, which is designed to collect the used washing liquid and in which the soil coming from the potatoes, which are to be treated, is separated from the washing liquid, for instance by letting the washing liquid stand still, whereby the soil settles. This settled soil is filtered and washed with a small amount of clean water in order to recover the salts, and the soil is then stored. The washed potatoes are dried with a current of air directed from above.

The cleaned washing fluid is recirculated back to the electrolytic cell.

In the following, the production of the washing chemicals will be examined in more detail

In order to produce the washing liquid containing hypochlorite and possibly chlorate, a salt solution is led into the electrolytic cell, which is arranged in conjunction with the washing station. When an electric current is led between two electrodes in the salt solution (e.g. an aqueous solution of NaCl), chlorine is produced at the anode and NaOH at the cathode, both of which react immediately with each other in the open electrolytic cell and form hypochlorite, NaOCl. Hypochlorite disintegrates slowly in the presence of organic substances, according to the formula below:

2 NaOCl → 2 NaCl + O₂

Before the oxygen is transformed into O₂ molecules, it is in an active state [O ], which oxidizes organic substances. Hypochlorite has a much longer-term effect than the oxygen, which is formed when ozone disintegrates, because hypochlorite disintegrates more slowly.

On the anodic side of the electrolysis the hypochlorite reacts with water and forms chlorate in small quantities in accordance with the intensity of the current and as a function of the pH and the temperature. Furthermore, the chlorate formed partly forms perchlorate on the anodic side. Chlorate and perchlorate are slower oxidizers than hypochlorate but the amount of oxygen is bigger and thus long-term disinfection is achieved with these small amounts of chlorate and perchlorate.

All these generated oxidizers are decomposed back into salt, NaCl or KC1, which, while circulating in the washing water, is oxidized again and again into hypochlorate and to a small extent into chlorate and perchlorate. The preparation of active oxygen through the formation of hypochlorite requires approximately only 3-4kWh of electric energy per kilogram of active oxygen to be released.

The electrolytic cell and the electrodes can be made of any suitable material. It is advantageous to use RuO₂ as a coating material that does not favour the formation of oxygen. The carrier of the electrode is titanium. The electrodes are made of noble metals or coated with noble metal oxides, such as Pt, Ir or RuO₂.

In order to clean the electrolysis surfaces the direction of the current in the electrolytic cell can be changed. The voltage of the electrolytic cell can be set at between 2.5 V and 6 V to vary the relative amounts of the hypochlorate and chlorate salts, which are produced in the electrolysis. The electrolytic cell is typically of the flow-through type and it has an input nozzle which is connected to the outlet nozzle of the water-collecting device, for instance with a tube or a corresponding device. Furthermore, it is possible to connect to the input nozzle a fresh-feed pipe for the salt solution, in case it is desirable to increase the amount of salt in the circulation of the washing liquid (or to compensate for the amount of salt, which has been removed along with the washed root crop, see below). The outlet nozzle of the electrolytic cell is, in turn, connected to the spraying device of the washing station with a tube or a similar device.

When the potatoes are dried after the washing and the following disinfecting in a current of air, a thin layer of salt stays on the surface of the potato, preventing further re-contamination by microbes. In this layer of salt there are small amounts of chlorate and perchlorate, too. According to research, the potatoes tolerate this treatment even in a salt solution of 250 g/litre without any adverse effects on germinability. The Thai study quoted above supports the idea that the presence of small amounts of chlorates in the soil is an advantageous activator of the maturing of the crop.

When the potatoes are now planted in the ground, a small amount of salt is dissolved in the water and the potatoes start to germinate in a normal way. According to the present invention, a long-term disinfecting effect is achieved in a very affordable way, and, at the same time, the environment is protected, because no toxic substances are released. The salt is extracted from the surface of the potato and the small amounts of chlorates are decomposed back into table salt when they come into contact with organic substances.

According to our experiments, sulphonated surface-active agents containing amines or quaternary ammonia should not be used, because they are easily oxidized by the hypochlorite as well as by the process of electrolysis itself.

The method according to the invention is suitable for washing and disinfecting root crop and especially seed potatoes, but it can also be applied to disinfecting bulbous roots of other cultivated plants, such as bulbous plants.

Claims

Claims:

1. A method for washing and disinfecting root crop, according to which method the root crop is washed with an aqueous washing liquid, characterized in that - the washing liquid used is an aqueous solution containing hypochlorite, which is prepared from a chloride salt by electrolysis, and possibly chlorates, which are prepared for the washing liquid immediately before they are used, the solid impurities are separated from the used washing liquid, and the purified washing liquid is recovered and recirculated for the production of hypochlorite and chlorate.

2. A method according to Claim 1, characterized in that the washing liquid is generated by leading water, in which chloride salt is dissolved, through an electrolytic cell (6), whereby hypochlorite and chlorates are produced from the chloride salt by electrolysis, after which surface-active agents are mixed into the electrolysed water.

3. A method according to Claim 1 or 2, characterized in that the washing liquid is led into washing equipment, in which the potatoes or the root crop is washed with a washing liquid spray, - the washed potatoes or root crop are dried in a current of air, the soil, which has been recovered from the washing and which has settled from the washing water, is filtered, and the water is recirculated back into the electrolytic cell.

4. A method according to any of the preceding claims, characterized in that the washing liquid contains 0.01-0.5% by weight surface-active agents and 3-10% by weight hypochlorate and chloride.

5. A method according to any of Claims 2-4, characterized in that the surface-active agent is a poorly oxidizable agent containing alcohol or ether groups.

6. A method according to any of Claims 2-5, characterized in that the surface-active agent used is isopropyl alcohol, pine soap, octyl phenol ethoxylate or a corresponding agent

7. A method according to any of Claims 1-6, characterized in that the washing liquid is prepared using an electrolytic cell (6), the voltage of which is set at a value between 2.5V and 6 V in order to vary the relative amounts of the hypochlorate and chlorate salts that are produced in the electrolysis.

8. A method according to any of the preceding claims, characterized in that an electrolytic cell (6) is used to prepare the washing liquid, in which cell the anode and the cathode are made of noble metals, such as platinum or iridium, or they are coated with noble metal oxides, such as RuO₂-

9. A method according to any of Claims 1-8, characterized in that an electrolytic cell (6) is used to prepare the washing liquid, in which cell the direction of the current is changed in order to clean the electrodes.

10. A method according to any of the preceding claims, characterized in that the soil that is separated from the washing liquid is reused.

1 1. An apparatus for washing root crop with an aqueous washing liquid, characterized in that it comprises a washing station, which has spraying equipment (1) for washing the root crop to be treated, and water-collecting equipment (4) for collecting the used washing liquid, - an electrolytic cell (6) for preparing the washing liquid, devices for leading the washing liquid from the electrolytic cell (6) to the spraying equipment (1), and devices for leading the used washing liquid from the water-collecting equipment (4) to the electrolytic cell.

12. An apparatus according to Claim 11, characterized in that the washing station comprises an essentially horizontal conveyor belt for transporting the root crop from the receiving station to the discharge station by lifting locally from below, and spraying equipment (1) placed above the conveyor belt and water-collecting equipment (4) placed below it.

13. An apparatus according to Claim 1 1 or 12, characterized in that the water collecting equipment (4) contains filtering devices for filtering the soil.

14. An apparatus according to Claims 11-13, characterized in that the water-collecting equipment (4) contains settling devices for settling the soil.

15. An apparatus according to any of the preceding claims, characterized in that the electrolytic cell (6) is open.

16. An apparatus according to any of the preceding claims, characterized in that the electrodes of the electrolytic cells (6) are coated with noble metals or noble metal oxides.