JPH0242473B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to particles for adhesion of microorganisms, and more specifically to cylindrical particles made of synthetic resin for adhering to and supporting microorganisms used in water treatment and fermentation production, the outer surface of which is roughened to act as an adhesion agent for microorganisms. This invention relates to cylindrical particles with improved properties. Here, the term cylindrical particles refers to particles that are hollow through the particles and have a cut end, that is, a cross section, that is circular, elliptical, or polygonal (for example, triangular to dodecagonal, including star-shaped particles). BACKGROUND ART Conventionally, techniques covering a wide range of fields such as filtration, sedimentation separation, and biological treatment have been proposed for methods of treating wastewater such as domestic wastewater and industrial wastewater. Among these methods, methods have been developed that use carriers floating in water to effectively carry out filtration, biological treatment, etc. Furthermore, in fermentation for the purpose of producing specific useful substances, fixed microbial membrane methods have also been adopted, in which a carrier with a specific gravity lighter than the culture solution is used, and microorganisms are attached to the carrier to carry out fermentation. There is. The lightweight particles used in these methods include natural lightweight particles such as pearlite and shirasu balloons, synthetic resin particles with a specific gravity of less than 1, and synthetic resins made to have a low specific gravity by foaming, such as foamed Particles such as polyethylene, foamed polypropylene, and foamed polystyrene, which are already commercially available for purposes such as fillers, adsorbents, and heat insulating materials, are used. However, since lightweight natural materials easily absorb water, it is difficult to use them as particles that float on water semi-permanently. In addition, although synthetic resin particles with a low specific gravity have the advantage of being able to obtain uniform particles in large quantities, the adhesion strength between the microbial membrane and the particle surface is low, so there is a risk of friction between particles or between particles and the vessel wall, and between particles and water. In addition, there is a disadvantage that part or all of the microbial membrane may be peeled off due to shearing caused by air bubbles (hereinafter simply referred to as contact between particles), and from an economic point of view, the synthetic resin raw material is expensive, so particles The cost also becomes high. Under these circumstances, the present inventors found that the particles obtained by foaming a mixture of synthetic resin and inorganic material as the main component have excellent hydrophilicity, and have extremely high adhesion of microbial membranes. By changing the ratio of resin and inorganic material, most of the air bubbles in the particles are maintained as closed cells, so we discovered that they can be used as particles that float semi-permanently on water, and we have created a new particle for supporting microorganisms for water treatment. (Unexamined Japanese Patent Publication No. 1983)
−89897). Furthermore, as an improved version of the low-density particles, we developed low-density particles for supporting microorganisms, which are made by attaching inorganic and/or organic substances of a specific particle size to the surface of a foamed synthetic resin (patent application 1983-
No. 131241). This method not only increases the expansion ratio of the synthetic resin and reduces the amount of synthetic resin used as much as possible, but also has the feature that the specific gravity of the particles can be easily adjusted. However, what these particles for supporting microorganisms have in common is a treatment method in which microorganisms are attached to and supported on the particles and used without being fixed in a liquid.
For example, treatment methods using fluidized beds, mixed beds, etc. have the advantage of not being clogged by proliferating microorganisms that occur in treatment methods using fixed beds, and can maintain high concentrations of microorganisms, resulting in high reaction rates. However, the surplus microorganisms that separate from the particles are minute and have poor sedimentation properties, so when using a conventional gravity sedimentation tank for separating SS caused by surplus microorganisms in the latter stage, the equipment must be used to some extent. The disadvantage was that it had to be made larger. Therefore, in such water treatment methods, it has been desired to obtain surplus microorganisms with good sedimentation properties. The purpose of the present invention is to eliminate the above-mentioned drawbacks, discharge surplus microorganisms with good sedimentation properties, and provide microorganism adhesion particles that generate a small amount of surplus microorganisms and have excellent adhesion of microorganisms. be. The present invention provides cylindrical particles made of synthetic resin with a specific gravity of less than 1, which have an outer diameter of 1.5 to 15 mm, a length to outer diameter ratio of 0.2 to 6.0, and a wall thickness of 0.05 to 1.0 mm. These are particles for attaching microorganisms, which are made by roughening the outer surface of certain cylindrical particles by physical means. The synthetic resin used in the present invention has an apparent specific gravity of less than 1, and thermoplastic resins are particularly preferred, and specific examples thereof include polyethylene, polypropylene, polystyrene, and methylpentene polymers. Here, these synthetic resins should be interpreted in a broad sense; for example, taking polyethylene as an example, it includes not only homopolymers of ethylene but also copolymers of ethylene and other olefins. Furthermore, the present invention also includes synthetic resins that are foamed to have a specific gravity of less than 1.0. Cylindrical particles are obtained by applying known molding means to synthetic resin, and as mentioned above, the particles are hollow particles with a through hole, and the cut end, that is, the cross section is circular, elliptical, polygonal, etc. It is something. Common polygons include triangles, quadrilaterals, and hexagons.
Any shape up to the size of a dodecagon including a star shape is possible.
Cylindrical particles can be easily obtained, for example, by cutting a molded product obtained by extrusion molding into a certain length with a cutter, etc., but it is easy to manufacture and has a uniform microbial film. A material with a circular cross section is preferred because it is thick enough to be easily adhered to and has a large specific surface. The cylindrical particles of the present invention have an outer diameter of 1.5 to 15 mm, and the smaller the outer diameter, the larger the specific surface area, which is preferable, but if the outer diameter is less than 1.5 mm, the particles Because the particles adhere to each other due to the microorganisms attached to the surface, efficient water treatment cannot be performed, and because the inner surface of the particles is filled with microorganisms, the inside of the particles does not work effectively for reactions. becomes. On the other hand, if the outer diameter exceeds 15 mm, the amount of microorganisms retained decreases as the specific surface area decreases, and the reaction rate per unit volume decreases, resulting in a decrease in the reaction rate of conventional methods such as rotating disks, sprinkled beds, and submerged beds. , and the features of the present invention are lost. From the standpoint of reaction rate, the most preferred outer diameter of the particles is in the range of 1.5 to 10 mm. however,
When treating wastewater containing sugars, starches, etc., the film thickness of attached microorganisms becomes abnormally large, and if small particles are used, they may adhere to each other. Outer diameter is 10
It is suitable to use particles of about ~15 mm. Regarding the outer diameter of the cylindrical particles, if the cross section is other than circular, the equivalent circular diameter may be treated as the outer diameter. Next, the ratio (L/
D) should be between 0.2 and 6.0; if this ratio is less than 0.2, it will be difficult to retain microorganisms in the hollow interior, and the features of the present invention, such as a reduction in the amount of surplus microorganisms produced and good sedimentation properties, will be lost. I'm getting used to it. On the other hand, if this value exceeds 6.0, the length of the particles is too long and the mobility of the particles becomes poor during use.For example, when used in a fluidized bed, fluidity is significantly inhibited, and the particles are generated by microbial reactions. The disadvantages are that the aeration gas is encapsulated inside the cylindrical particles, which reduces the apparent specific gravity of the particles, and that microorganisms cannot be sufficiently retained inside the particles. Moreover, when this value is large, the packing efficiency of particles also decreases. Therefore, it is generally preferable that the ratio (L/D) is in the range of 0.5 to 3.0. In addition, the wall thickness of the cylindrical particles must be 0.05 to 1.0 mm, and if the wall thickness is less than 0.05 mm, the particle transport
They are easily damaged during storage, and if the diameter exceeds 1.0 mm, not only will the specific surface area of the inner surface of the cylindrical particles decrease, but the amount of synthetic resin used will increase, leading to higher costs. Although the diameter of the hollow portion varies depending on the outer diameter and wall thickness of the particle, it is usually preferably 1 mmφ or more. Furthermore, the microorganism-adhesive particles of the present invention have improved adhesion of microorganisms by roughening the outer surface by physical means. By performing this treatment, the amount of microorganisms retained per unit volume of particles can be increased. When particles are used for water treatment by forming a fluidized bed, mixed layer, transport layer, etc. without roughening the surface, most microorganisms usually adhere to the outer surface of the cylindrical particles due to contact between the particles. I won't. Such a phenomenon is undesirable from the standpoint of efficiently attaching microorganisms to particles and utilizing them. Therefore, roughening the outer surface is important for cylindrical particles for microbial attachment. Methods for roughening the outer surface of particles include, for example, a method in which the surface is heat-treated before cutting a molded object obtained by extrusion molding into a certain length, and a method in which the surface is etched using an acid such as concentrated sulfuric acid. . Although there are methods of processing by mechanical (that is, physical) means using an abrasive or the like, surface roughening treatment by physical means is most preferable. Physical surface treatment improves the adhesion of microorganisms by creating irregularities, folds, and scratches on the surface of particles, and also prevents most of the attached microorganisms from easily detaching even when particles come into contact with each other. can do. A more detailed study of the roughening state of the particle surface and the adhesion of microorganisms reveals that the difference in the roughening state due to the difference in the surface roughening treatment method has a great effect on the adhesion of microorganisms. In other words, unevenness is formed on the surface of particles that have been thermally or chemically treated, but these unevenness are generally smooth, and the adhesion of microorganisms is much greater than in the case of no treatment. However, microorganisms are relatively easily detached due to contact between particles. On the other hand, particles whose surfaces have been roughened by physical (mechanical) means have surface flaws such as "scratches" and "hangnails" on their surfaces. These surface flaws make it easy for microorganisms to adhere to the surface, and the microorganisms are also difficult to peel off due to contact between particles. When similar physical means are applied to cylindrical particles whose specific gravity has been lowered by adding a foaming agent to a synthetic resin, even sharper surface scratches are observed, but these occur near the surface of the cylindrical particles. This is thought to be due to the fact that closed cells are destroyed by physical treatment. As mentioned above, microorganisms are easily attached to particle surfaces that have sharp "scratches" and "hangnails".
It was found that the number of days required for adhesion is short, and that the attached microorganisms are difficult to separate even if the particles come into contact with each other. Therefore, in the present invention, cylindrical particles subjected to physical roughening treatment are preferred. Physical roughening treatment means include, for example, applying an abrasive or an abrasive brush to the surface of a cylindrical molded product obtained by extrusion molding, or using one or more sharp blades to scratch the surface. There are ways to attach it. Such treatment methods include fixing a surface treatment machine and continuously moving the cylindrical molded product, or rotating or reciprocating the machine to continuously treat the cylindrical molded product. Continuous operation is usually performed. Next, the surface-treated cylindrical molded body is cut into a predetermined length to obtain particles for attaching microorganisms of the present invention. Particles that have been subjected to physical roughening treatment have good adhesion to microorganisms, so the material for these particles should have a specific gravity of about 0.6 to 0.9 to prevent the particles from settling even when microorganisms are attached. Should be used. As mentioned above, the cylindrical particles of the present invention are made into a constant molded body by extrusion molding, etc., so that a uniform wall thickness is obtained, and then cut into a predetermined length with a cutter etc., so that the length can be adjusted. Almost uniform. Therefore, the shape is uniform and the specific gravity is constant, so that some particles do not settle during use and good fluidity can be obtained. What is also noteworthy is that the surplus microorganisms discharged from the microorganism treatment equipment using the cylindrical particles of the present invention have significantly better sedimentation properties than conventional ones, so they can be used in the subsequent stages.
The sedimentation tank and overtank for SS separation can be downsized, and treated water with extremely high transparency can be obtained after SS separation. Another feature of the present invention is that the amount of SS discharged is smaller than when conventional particles are used. Although the cylindrical particles of the present invention are used for water treatment and fermentation production, they are also suitably used for methods other than fixed bed methods, that is, methods other than water treatment using fixed bed equipment, such as fluidized It can be advantageously applied to a method of forming and processing a fluidized bed, mixed layer, transport layer, etc. using a bed device, complete mixing device, etc. In that case, the processing methods include downward flow, cross flow,
Any type of upward flow may be used; in the case of upward flow, a fluidized bed or a mixed bed can be formed by blowing gas. When water treatment is performed using conventional particles, the particles are constantly in contact with each other in a biological reaction tank in which microorganisms are attached to the particles to form a fluidized bed, mixing tank, etc. A portion of the excess microorganisms that have proliferated and adhered are constantly peeled off and flowed out of the system. However, these surplus microorganisms have extremely high activity and are microscopic, so they have poor sedimentation properties. Therefore, in order to obtain clear treated water,
Measures such as preparing a large gravity settling tank and adding a flocculant are required. However, when the cylindrical particles of the present invention are used, the microorganisms that proliferate and adhere to the outer surface of the particles are not easily peeled off even when the particles come into contact with each other, and the adhesion time to the particles is long. Further, microorganisms that grow and adhere to the inner surface of the cylindrical particles are not separated by contact between the particles, but are separated by the flow of water or gas passing through the interior of the cylindrical particles.
At this time, the force applied to the excess microorganisms is smaller than the force applied to the excess microorganisms present on the outer surface, so the amount of microorganisms to be peeled off is smaller than that on the outer surface, and the time for the microorganisms to adhere to the particles becomes longer. Therefore, the viscosity of the microorganisms attached to the inner surface of the cylindrical particles increases, the bonding force between microorganisms becomes large, and in order to capture suspended microorganisms that are fine and have poor sedimentation properties, the flow of water and gas increases. The excess microorganisms detached by this process have a high flocculation property and exhibit good sedimentation properties. Furthermore, in addition to capturing suspended microorganisms as described above, microorganisms attached to the inner surface of the cylindrical particles are more difficult to peel off than microorganisms on the outer surface. As a result, the residence time of microorganisms increases, and aerobic digestion occurs, reducing the amount of sludge. Next, an example of use of the cylindrical particles of the present invention will be shown. Usage example A water treatment experiment was conducted using hollow cylindrical particles (material: polypropylene) with different surface roughening treatments, and the adhesion rate of microorganisms, adhering microorganism concentration, treated water BOD, and treated water SS sedimentation rate were determined as follows. It was determined using a downward flow fluidized bed apparatus. It has a built-in air lift tube 4 as shown in Fig. 1, and the lower part of the air lift tube 4 and the reaction part 3
A microbial reaction tank A equipped with an aeration pipe at the bottom was filled with various particles as shown in Table 1, and waste water was supplied from the top of the reaction tank using a pump 2. On the other hand, part of the treated water that rises in the air lift tube with the air lift is mixed with raw water and passed in a downward flow to the reaction section filled with particles with microorganisms attached, and aeration is carried out from the air diffuser tube. Air was supplied to the particle layer in the reaction section, and the organic matter in the wastewater was aerobically treated with microorganisms. The processing conditions are as follows. Reaction tank: 4 units made of polyvinyl chloride resin, diameter 4B, height approx. 80cm (capacity approx. 6) Particle filling amount: Approx. 2 Raw water: Fish meat extract dissolved in tap water Raw water supply amount: Approx. 2 /hr Fluidized bed expansion: approximately 1.5 to 2 of the static bed height
Air is supplied from the bottom of air lift tube 4 so that it doubles. Note that air was supplied from the diffuser pipes 5a and 5b, and the amount of air was adjusted so that dissolved oxygen in the treated water could be maintained at 1 ppm or more. Experiment period: 25 months Average water temperature: 20.7℃ Raw water BOD: Approx. 200ppm

[Table] Figure 6 shows the results of continuous experiments using each particle regarding the rate of attachment of microorganisms and the concentration of attached microorganisms. In Figure 6, Mixed Liqur Suspended
Solid (MLSS) represents the microbial concentration. For MLSS measurement, 100c.c. of particles were extracted from four reaction vessels.
The sample was placed in a 0.3N sodium carbonate solution, stirred, and the concentration of detached microorganisms was determined. Figure 6 shows the menstrual changes in MLSS. As is clear from FIG. 6, particles subjected to physical surface treatment have a high MLSS concentration and an extremely excellent ability to retain microorganisms, regardless of foaming or non-foaming.
Furthermore, regarding the rate of attachment of microorganisms, rapid attachment occurs within one month, after which the concentration of microorganisms reaches equilibrium. The MLSS concentration at equilibrium is
It reached 18,000 to 20,000 ppm, and was found to retain microorganisms at an extremely high concentration compared to particles No. 3 and No. 4. On the other hand, particle No. 3 with chemical surface treatment has a slower microbial adhesion rate than particles with physical surface treatment, reaching an almost equilibrium state in 1.5 to 2 months, but the MLSS concentration at that time Somewhat less hazy
Less than 5000ppm. Furthermore, particles No. 4 whose particle surfaces were not subjected to surface roughening treatment had almost no adhesion of microorganisms for about one month. Although the MLSS increased after 1.5 months, the outer surface was shiny due to particle-to-particle contact, and almost no microorganisms were attached.
The increase in MLSS is considered to be due to microorganisms that adhere to and proliferate on the inner surface of the inner cylinder. Therefore, the MLSS concentration at equilibrium showed the lowest value among the four types of particles. Table 2 shows the SS sedimentation rate of the treated water and the BOD concentration (average value) of the treated water after 1.5 to 2.5 months of almost equilibrium.

[Table] Simultaneous comparative experiments on the four types of particles mentioned above revealed that microorganisms easily adhere to the surfaces of particles whose surfaces have been physically treated and have many surface scratches, and the concentration of microorganisms is also extremely high. It was found that the SS of the treated water was maintained at a very high quality, the quality of the treated water was very good, and the SS sedimentation rate of the treated water was extremely fast.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the aerobic treatment device, and the second
Figures 5 to 5 are sketches of examples of particles of the present invention. FIG. 6 is a graph showing menstrual changes in MLSS. 1...Raw water supply pipe, 2...Pump, 3...Reaction section, 4...Air lift tube, 5a, 5b...
... Diffuser pipe, 6... Treated water extraction pipe, A... Reaction tank.

Claims (1)

[Claims] 1. Cylindrical particles made of synthetic resin with a specific gravity of less than 1, with an outer diameter of 1.5 to 15 mm and a length to outer diameter ratio of 0.2.
6.0 and a wall thickness of 0.05 to 1.0 mm, the outer surface of the cylindrical particles is roughened by physical means. 2. Particles for attaching microorganisms according to claim 1, wherein the synthetic resin is a thermoplastic resin.