JP2013009644A - Bactericidal device for culture solution for hydroponics using membrane filtration, and method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and simple bactericidal device for a culture solution which can be used for a small-scale of hydroponics system, and to provide a method for eliminating bacteria.SOLUTION: The bactericidal device 1 for a culture solution for hydroponics includes: a filtration tank 2 and a flat plate type membrane module 3 using a microfiltration membrane or an ultrafiltration membrane; and an air diffusion device 5 provided under the flat plate type membrane module 3. In the bactericidal device 1, the module is inexpensive, the configuration of the bactericidal device is simple, and continuous operation can be carried out without replacing the membrane module for a long period of time.

Description

  The present invention relates to a culture solution sterilization apparatus and method for preventing crop diseases in hydroponics such as hydroponics and rock wool cultivation.

  Plant culture such as vegetables, fruits, flowers, etc. is a cultivation method that supplies nutrients and minerals necessary for plants in a culture solution without using a culture medium or using rock wool instead of soil as a culture medium It is. Compared to soil cultivation, it has been popularized because it has no continuous cropping problems, can eliminate weeding, and can use fertilizer without any loss of fertilizer.

  However, when the culture solution is used for a long period of time, disease germs propagate, and the disease may spread within a short time and the crop may be annihilated. For this reason, a flow-through method that does not circulate and recycle the culture solution is adopted, and empirical measures such as disinfection with chemicals and replacement of the culture solution are often taken before the period when pathogens occur, and nutrients are wasted Often discarded. Moreover, since the used culture solution contains a large amount of nitrogen, phosphorus and other inorganic salts, it is not preferable to discharge it to a river or the like because it causes an increase in environmental load.

  If the used culture solution can be sterilized and reused, it is possible to prevent the growth of pathogens, reduce the amount of culture solution used, and reduce the amount of used culture solution discarded. Then, development of the method of disinfecting and reusing a culture solution using membrane filtration has been performed for a long time.

  Patent Document 1 describes a method for purifying a nourishing culture solution using an ultrafiltration membrane. Patent Document 2 describes a method of disinfecting a culture solution in hydroponics by providing a microfiltration membrane in the culture solution circulation system. Patent Document 3 describes filtering raw liquid for culture solution using a reverse osmosis membrane in a nutrient solution cultivation apparatus. Patent Document 4 describes a hydroponic cultivation apparatus in which an ultrafiltration device is incorporated in a culture medium circulation path. Patent Document 5 describes a hydroponic cultivation apparatus provided with a hollow fiber membrane filtration device using a reverse osmosis membrane or the like for sterilization in a nutrient solution circulation path. Patent Document 6 describes that in a culture solution purification apparatus using membrane filtration, the frequency of replacement of the filtration membrane is reduced by air scrubbing and chemical washing. Patent Document 7 describes a cultivation system for removing plant phytopathogens in a plant cultivation system using a filtration membrane having a membrane pore diameter of 0.5 nm to 0.5 μm while allowing nutrients contained in the liquid to pass through. Yes.

  Most of the above-mentioned patent documents disclose an apparatus or a method using a hollow fiber membrane because the filtration membrane area is large. In patent document 1, there is no description regarding the format of a filtration membrane or a module other than a filtration membrane being an ultrafiltration membrane. Further, in Patent Document 4, tubular membranes, flat membranes, spiral membranes, and hollow fiber membranes are listed as membrane shapes, but what is specifically disclosed in the examples is the limit described in the specification. It can be seen from the product number of the outer filtration membrane that the device and method use a hollow fiber membrane.

JP-A-53-75032 JP-A 63-294717 Japanese Utility Model Publication No. 03-018743 JP 09-107826 A JP 2001-346460 A JP 2002-204933 A JP 2007-195410 A

  However, when a hollow fiber membrane or a flat membrane with a spiral type or pleated type filtration module is used for the culture medium sterilization device, the module is expensive and when foreign matter such as root hair is clogged It was difficult to recover the filtration performance, and there was a problem that the nutrient solution was acidified due to the decay of the residual root and the frequency of module replacement was increased. Further, there is a problem that the entire equipment becomes complicated and expensive in order to increase or control the supply pressure of the processing liquid. Therefore, it was economically difficult to adopt such a sterilization apparatus for a small-scale hydroponic cultivation system.

  The present invention has been made in consideration of the above points, and an object of the present invention is to provide an inexpensive and simple culture solution sterilization apparatus that can be used in a small-scale nutrient solution cultivation system. In addition, an object is to provide a sterilization method using the sterilization apparatus.

  The sterilization apparatus for nutrient solution culture liquid of the present invention includes a filtration tank, a flat membrane module provided in the filtration tank, using a microfiltration membrane or an ultrafiltration membrane, and below the flat membrane module And an air diffuser provided in the apparatus.

  Since a flat plate type membrane module using a microfiltration membrane or an ultrafiltration membrane and having a simple structure compared to a spiral type or a pleated type is used, the module itself is inexpensive and the entire structure of the sterilizer is simple. It will be a thing. In addition, since the filtration process can be performed while efficiently washing the filtration membrane surface by the cross flow method by the aeration from the aeration device, it is the pressure difference between the primary side and the secondary side of the filtration membrane. The transmembrane pressure difference converges to a certain value over time, and continuous operation can be performed for a long time without replacing the membrane module. In addition, since it is a flat plate type, it is difficult to clog foreign matter such as root hair, contributes to continuous operation, and because it is easy to collect foreign matter, the effect of preventing acidification of nutrient solution due to decay of residual root, Since the dissolved oxygen concentration in the culture solution is increased by aeration, the growth of crops is promoted, and the effect of increasing resistance to root pathogens is obtained.

In addition, the sterilization apparatus preferably further includes a stirring device that stirs the culture solution in the filtration tank.
As a result, when a membrane surface cleaning aid is added to the culture solution, the cleaning effect of the filtration membrane surface by crossflow is increased, and it is more stable and continuous operation without replacement of the membrane module over a long period of time. It can be performed.

More preferably, the stirring device comprises a circulation pump for circulating the culture solution in the filtration tank and a pipe.
Thereby, the configuration of the apparatus becomes simpler.

  The sterilization method of the hydroponic culture solution of the present invention uses any one of the sterilization apparatuses described above, adds powder as a membrane surface cleaning aid to the filtration tank, and continuously performs the aeration apparatus. While operating, the culture solution is filtered by a cross flow system while the stirring device is operated continuously or intermittently.

  Since a flat membrane module is used in the present invention, by operating the diffuser, a cross flow in which the culture solution in the filtration tank rises along the filtration membrane surface is generated, and the effect of washing the filtration membrane surface is obtained. . In addition, the powder, which is a membrane surface cleaning aid added to the culture solution, has a function of scraping the deposits on the filter membrane surface. By moving the stirring device, the powder settles in the filtration tank. And can be dispersed in the culture medium. Thereby, according to the sterilization method of the present invention, continuous operation can be performed over a long period of time without replacement of the membrane module. Furthermore, since the dissolved oxygen concentration in the culture solution is increased by aeration, the growth of crops is promoted and the resistance to root pathogens is increased.

The sterilization method is preferably characterized in that the powder that is a cleaning aid for the membrane surface is neutral. Thereby, the fluctuation | variation of the pH of the culture solution by adding powder can be suppressed, and it can prevent a bad influence on the growth of a crop.
More preferably, the neutral powder which is a cleaning aid for the film surface is diatomaceous earth.

  As described above, according to the sterilization apparatus and sterilization method of the hydroponic culture solution of the present invention, the filtration module is inexpensive, the configuration of the apparatus is simple, and continuous operation is performed without replacement of the membrane module over a long period of time. Since it is economical, it is possible to sterilize and reuse the culture solution even in a small-scale hydroponics system, and the dissolved oxygen concentration in the culture solution becomes high, so that the growth of the crop Is promoted, and the resistance to root pathogens is increased.

It is a block diagram of the hydroponic cultivation system using the culture solution disinfection apparatus which is one Embodiment of this invention.

  One embodiment of the culture solution disinfection apparatus of the present invention will be described with reference to FIG.

  FIG. 1 shows a configuration of a hydroponic cultivation system using the sterilization apparatus of the present embodiment. The culture solution discharged from the hydroponics shelf 11 is sent to the culture solution sterilization apparatus 1 provided in the culture solution circulation path by the liquid feed pump 12, and the sterilized culture solution is reused and hydroponically. Returned to the cultivation shelf 11.

  The culture solution sterilization apparatus 1 according to this embodiment includes a filtration tank 2, a flat membrane module 3 provided in the filtration tank 2, an aeration tube 5 provided below the circulation tank 2, and a circulation for circulating the culture solution in the filtration tank. A pump 6 and a circulation pipe 7 and a suction pump 9 for suction filtration are provided.

  The flat membrane module 3 may have various known structures. For example, flat membrane elements with flat membrane (sheet membrane) or ultrafiltration membranes arranged on both sides of the filter plate are placed vertically, and one or more sheets are arranged in the plane direction at intervals Things can be used.

  If the structure of the said filtration membrane is a flat membrane, various well-known things can be used. For example, a synthetic resin nonwoven fabric having a polymer film having a large number of pores formed on the surface thereof can be used.

As the type of the filtration membrane, a microfiltration membrane or an ultrafiltration membrane is used.
Here, regarding the microfiltration membrane and the ultrafiltration membrane, there is no established definition represented by the pore diameter and the boundary between them is not clear. According to the physics and chemistry dictionary (5th edition, Iwanami Shoten), when the particle size of the material to be filtered is 0.02 to 10 μm, microfiltration is performed, and when 0.001 to 1 μm (molecular weight is 1000 to 300,000), ultrafiltration is performed. It is said. Therefore, a filtration membrane having the same pore diameter may be referred to as a microfiltration membrane or an ultrafiltration membrane.
In the present specification, the terms microfiltration and ultrafiltration are used according to the above definitions, but when the pore diameter should be defined more precisely, the nominal pore diameter is used. In addition, a nominal pore diameter means the particle diameter when the particle | grains of the size can be captured 98%.

Since the purpose of the filtration membrane used in the present invention is to remove pathogens in the culture solution, it is necessary to select an appropriate filtration membrane for that purpose. The approximate size of the pathogen is several μm or more for fungi and about 0.5 to 2 μm for bacteria. In hydroponic culture, the diseases of the underground that affect the roots of crops are important, and among these pathogens, the most frequently occurring are the so-called aquatic fungi (egganoid flagellates) (for example, Soichi Kusakari, “Disease and Countermeasures of Hydroponic Culture”, Rural and Mountain Culture Association, 2009, p.21).
Accordingly, the filtration membrane preferably has a nominal pore size of 1 μm or less. This is because, when the nominal pore diameter is 1 μm or less, fungi that cause diseases that invade roots that are important in hydroponics can be efficiently removed. The filtration membrane preferably further has a nominal pore size of 0.5 μm or less. This is because if the nominal pore size is 0.5 μm or less, bacteria smaller than the fungi can be efficiently removed. On the other hand, if the pore diameter is too small, problems such as an increase in filtration resistance and a decrease in the amount of filtration treatment occur. Therefore, the nominal pore diameter is preferably 0.1 μm or more.

  The air diffuser 5 is provided below the flat membrane module 3. When the air diffuser 5 diffuses air taken in from the outside by the blower 4, a cross flow in which the culture solution in the filtration tank 2 rises along the filtration membrane surface can be generated. The diffuser pipe 5 may be of various known structures, such as a pipe having one end closed and a large number of small holes provided on the upper surface.

  The circulation pump 6 and the circulation pipe 7 are provided so that the culture solution in the filtration tank 2 is sucked from the lower part of the filtration tank 2 and returned to the upper part for circulation.

  Next, the sterilization method using the sterilization apparatus of the above embodiment will be described with reference to FIG. 1, and the membrane surface cleaning aid used in the sterilization method will be described.

  The sterilization method of the present embodiment is performed by filtering the culture solution in the filtration tank 2 with the membrane module 3. To the filtration tank 2, powder that is a cleaning aid for the membrane surface is added. The circulation pump 6 is operated to suck the culture solution from the lower part of the filtration tank 2 and return to the upper part of the filtration tank 2 through the circulation pipe 7. By performing aeration from the aeration tube 5 by the blower 4, the culture solution around the aeration tube 5 causes a cross flow that rises along the filtration membrane surface of the membrane module 3. By performing the suction filtration by operating the filtration suction pump 9, the culture solution in the filtration tank 2 is sterilized and applied again to the hydroponics shelf.

  In cross-flow filtration, the flow resistance of the cross-flow increases when the deposit on the filtration membrane surface increases, so the thickness of the deposit layer and the transmembrane pressure difference tend to converge to a certain value over time. . In a module such as a hollow fiber membrane, a spiral type, or a pleat type, if foreign matter is clogged between membranes, the liquid flows preferentially to other parts, so that the foreign matter may not be easily removed by cross flow. On the other hand, in the flat membrane module, the thickness of the deposit layer and the transmembrane pressure difference tend to converge due to the structure. Therefore, the flat membrane module can be continuously operated without replacing the membrane module over a long period of time and without performing chemical cleaning or physical cleaning performed by taking the membrane module out of the tank.

  The function of the powder, which is a cleaning aid for the membrane surface, is to enhance the cleaning effect of the filtration membrane surface by cross flow by scraping the deposits on the membrane surface by friction. Since the pore size of the filtration membrane used is small enough to remove pathogens, the function of a general filter aid such as forming a precoat layer on the filtration membrane surface is not required. In addition, the function of adsorbing and removing any components mixed in the culture solution is not required. In the sterilization method of the present invention, it is not excluded to use a powder having an adsorption / removal function or the like, or to use a powder having an adsorption / removal function or the like. It is necessary to use the body.

  The powder, which is a cleaning aid for the membrane surface, passes through the filtration membrane and does not flow out of the sterilization apparatus 1 and does not clog the pores of the filtration membrane. It is preferably not less than the pore diameter, and more preferably not less than 5 μm. Moreover, it is preferable that a particle size is 50 micrometers or less so that this powder may disperse | distribute well in a culture solution.

As the powder that is a cleaning aid for the membrane surface, diatomaceous earth, colloidal silica, activated carbon, cellulose powder, and the like can be used. Among them, neutral ones are preferable, and neutral diatomaceous earth is used. Further preferred.
Here, that the powder is neutral means that the pH of the aqueous suspension of the powder is neutral. The pH of the aqueous suspension can be determined according to, for example, the method of JIS K5101.

  If the powder is not neutral, the pH of the culture solution may vary due to the addition of the powder, which may adversely affect crop growth. For this reason, after adding the powder, it is necessary to wait for the pH of the culture solution to stabilize and to adjust the pH to a range suitable for the crop. For example, when activated carbon is used, pH fluctuations should be carefully monitored because their acidity varies with manufacturing conditions and is often not stable.

  In contrast, diatomaceous earth is readily available with a neutral and stable acidity. Moreover, diatomaceous earth is naturally derived and widely used in the fields of food industry and pharmaceuticals, and is also preferable in that it can be obtained at low cost.

The effects of the sterilization apparatus and sterilization method of the present invention will be described based on examples.
The test of a present Example was performed using the leaf culture | cultivation system of leaf lettuce. The configuration is shown in FIG. Hydroponic cultivation shelf 11 is a specification which fills and cultures a total of 350L of culture solution. Conventionally, 35 L of the culture solution corresponding to 10% of this was replaced and discarded every day.

The test was performed by feeding the culture solution of the cultivation shelf 11 to the sterilization apparatus 1 and returning the entire amount of the filtered culture solution to the cultivation shelf 11. The capacity of the filtration tank 1 was 7L. As the membrane module 3, one flat membrane element in which flat membrane type microfiltration membranes having a nominal pore diameter of 0.25 μm and a membrane area of 0.05 m ² are arranged on both sides of the filter plate was used. The filtration operation was carried out under the initial conditions of a filtration linear velocity of 0.35 m / day (the amount of filtrate obtained per day was 35 L) and the amount of air diffused was 3.5 L / min.

  To the filtration tank 2, 0.6% by mass of neutral diatomaceous earth (Showa Chemical Industry Co., Ltd., Radiolite # 500) with a slight change in pH even when added to the culture solution was added. The average particle diameter of diatomaceous earth was 30 μm. Since this diatomaceous earth is larger than the fine diameter of the filtration membrane, it does not leak or flow out of the sterilization apparatus when mixed with the filtrate. During the test period, no additional diatomaceous earth was added.

  The diatomaceous earth is dispersed by the circulating flow of the culture solution generated in the filtration tank 2 by aeration, but the circulatory pump 6 was always operated during the test to disperse the diatomaceous earth more highly.

Table 1 shows changes in filtration flow rate, membrane suction pressure, and pH of the culture solution during the test period. The filtration flow rate is a value measured by the filtrate flow meter 10 of FIG. 1, and the membrane suction pressure is a value measured by the membrane suction side pressure meter 8.
During the test period of 65 days, 2275 L of the culture broth was reused without adding additional culture broth, thereby reducing the amount of waste. However, since the cultivation shelf 11 is an open system, pure water was added after the elapse of 36 days and 63 days in order to compensate for a decrease in water content in the culture solution due to transpiration from crops.

  During the test period, there was no generation of pathogenic bacteria on the cultivation shelf, and it was confirmed that the sterilization effect by the membrane could be maintained. Moreover, although the tendency for the pH of the culture solution to fall during the test period was observed, it was in a range that could be adjusted by the additional input amount of pure water. As shown in Table 1, with the addition of pure water, the pH changed in the direction of acidity was almost neutralized.

  The decrease in the membrane suction pressure during the test period (increase in the transmembrane pressure difference) was -15 kPa, which was a stable filtration operation from start to finish. Moreover, since the fluctuation of the transmembrane pressure difference is gentle, the control of the filtration suction pump was easy. It was also confirmed that continuous operation was possible over a long period of time without replacing the membrane module.

Further, when the circulation pump 6 is stopped, the diatomaceous earth gradually settles to the bottom of the filtration tank 2, but even in that case, the cleaning effect of the filtration membrane surface can be obtained only by the cross flow, and one of the diatomaceous earth settled by aeration. Since the part is wound up, the transmembrane pressure difference does not rise rapidly. This is because, as described above, the flat membrane module has a remarkably large membrane surface cleaning effect by crossflow compared to a hollow fiber membrane module or the like.
Therefore, even if the circulating pump is not necessarily operated continuously, the intended function can be exhibited by operating it intermittently.

In addition, this invention is not limited to the above embodiment or Example, Many deformation | transformation are possible within the technical idea of this invention.
For example, various known devices can be used as the air diffuser in addition to the air diffuser. In addition, the stirring device for the culture solution may be a blade-type stirring device provided in the filtration tank. In addition, when the particle size of the cleaning aid on the membrane surface is small, the specific gravity is light, and the addition amount is small enough, it is possible to sufficiently stir by aeration from the aeration tube. Can do.

  The sterilization apparatus and sterilization method of the nutrient solution culture solution of the present invention can be used for cultivation of various crops. Moreover, it can utilize for various hydroponics, such as hydroponics, rock wool cultivation, gravel cultivation, and pot cultivation.

DESCRIPTION OF SYMBOLS 1 Culture liquid disinfection apparatus 2 Filtration tank 3 Flat membrane module 4 Blower 5 Aeration pipe 6 Culture liquid circulation pump in filtration tank 7 Circulation piping 8 Membrane suction side (secondary side) pressure gauge 9 Filtrate suction pump 10 Filtrate flow rate Total 11 Hydroponics shelf 12 Liquid feed pump

Claims (6)

A filtration tank;
A flat membrane module using a microfiltration membrane or an ultrafiltration membrane provided in the filtration tank,
An air diffuser provided below the flat membrane module;
An apparatus for sterilizing a hydroponic culture solution. The sterilization apparatus for hydroponic culture solution according to claim 1, further comprising a stirring device for stirring the culture solution in the filtration tank. The said stirrer consists of a circulation pump and piping which circulate the culture solution in the said filtration tank, The sterilization apparatus of the nutrient solution culture solution of Claim 2 characterized by the above-mentioned. A method for sterilizing a nourishing culture using the sterilization apparatus according to claim 2,
Add powder that is a cleaning aid for the membrane surface to the filtration tank,
A culture solution is sterilized by a cross-flow method while the agitator is continuously or intermittently operated while the air diffuser is continuously operated. The method for sterilizing a hydroponic culture solution according to claim 4, wherein the powder as a cleaning aid for the film surface is neutral. 6. The method for sterilizing a nutrient solution culture solution according to claim 5, wherein the powder that is a cleaning aid for the membrane surface is diatomaceous earth.

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