JP2007090300A - Method for treating organic waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating an organic substance-containing liquid by a membrane separation activated sludge method without increasing the amount of generated excess sludge, capable of preventing troubles such as poor membrane permeability, foaming, the generation of scum, an increase in viscosity or the like for a long time and continuously, and stable; and a treatment apparatus. <P>SOLUTION: In the treatment of organic waste water by the membrane separation activated sludge method including operation A loading activated sludge with a flocculant and operation B for making a micro animal act on the activated sludge, the method for treating the organic waste water comprises implementing at least one time of the operation B during from before 3 days to after 7 days of the period of implementation of the operation A. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  INDUSTRIAL APPLICABILITY The present invention can be suitably employed in treating a liquid containing organic substances that are soluble in water, such as industrial wastewater and domestic wastewater discharged from food factories, etc., by the membrane separation activated sludge method. The present invention relates to a method for treating organic wastewater.

  In general, organic wastewater has been treated by an activated sludge method comprising an aeration tank and a sedimentation tank. Although this method can treat wastewater at a relatively low cost, the activated sludge cannot be maintained at a high concentration in the treatment tank due to the restrictions on solid-liquid separation called the gravity sedimentation method, and there is a problem that the treatment space is generally widened. there were. Moreover, since a part of the organic matter in the wastewater is used for the growth of sludge when it is treated, there is a problem that excessive sludge that is difficult to dispose as industrial waste is inevitably generated.

  In recent years, a membrane separation activated sludge method, in which solid-liquid separation is performed using a microfiltration membrane or an ultrafiltration membrane, has begun to spread. In this method, the activated sludge can be kept at a high concentration in the treatment tank, and a sedimentation tank is not required, so that the treatment space can be made compact and the treatment water quality can be improved. Moreover, by holding many microorganisms against the wastewater load, endogenous sludge respiration and auto-oxidation are promoted, and the amount of excess sludge generation is reduced compared to the activated sludge method. However, even in the membrane separation activated sludge method, problems with membrane permeability failure, foaming, generation of scum, increase in viscosity, and the like have been raised and remained as problems.

  Several methods have been devised to solve the above problems.

  Patent Document 1 discloses a method of adding a flocculant. The methods described in these documents have a remarkable effect in the short term in improving membrane water permeability, defoaming, and reducing viscosity, but if the flocculant is used repeatedly over a long period of time, the efficacy may decrease. there were. In addition, the amount of the flocculant added is not small, and the added flocculant is substantially retained and accumulated in the tank, so that the addition of the flocculant leads to an increase in the amount of sludge generated. In addition, when the addition of the flocculant is repeated while the effectiveness of the flocculant is reduced, the proportion of the flocculant in the sludge in the tank gradually increases and the biological activity decreases, so that excess sludge is discharged to maintain the treatment. On the contrary, it is necessary to increase the amount, and the advantage of the generation of the low excess sludge inherent in the membrane separation activated sludge method may be impaired.

  Moreover, although the method which applied the micro animal for the purpose of improving the filterability in a membrane separation activated sludge method is not found, as related information, patent document 2 has the surplus sludge in the normal activated sludge method using a micro animal. The method of reduction is shown. These methods using micro-animals are considered to have advantages in terms of environmental compatibility and operation costs, but have problems in terms of predation efficiency and sustainability by micro-animals. Moreover, depending on the case, as a result of healthy flocs being preyed by micro-animals, there is a problem that flocs may be subdivided and sludge filterability may deteriorate, and the quality of treated water may deteriorate. It was.

As described above, there is no technology in the prior art that can reduce the risk of trouble over the long term without impairing the effect of low excess sludge generation, which is an advantage of the membrane separation activated sludge method. It can be said that there was.
JP-A-8-332483 Japanese Patent Laid-Open No. 11-10198

  The present invention was made in response to the above-mentioned problems in the prior art, and its purpose is to prevent troubles such as poor membrane permeability, foaming, scum generation, and viscosity increase without increasing the amount of excess sludge generation. It is an object of the present invention to provide a stable method and apparatus for treating an organic substance-containing liquid by a membrane separation activated sludge method that can be avoided continuously for a long period of time.

  In order to solve the above problems, the present invention has the following configuration.

  (1) In the treatment of organic wastewater by the membrane separation activated sludge method including the operation A for adding the flocculant to the activated sludge and the operation B for causing the micro animals to act on the activated sludge, A method for treating organic wastewater, which is carried out at least once between before 3 days and after 7 days.

  (2) The method for treating organic wastewater according to (1), wherein the minute animals are composed of a group of minute animals mainly composed of non-filtered predators.

  (3) The organic wastewater treatment method according to (1) or (2), wherein the BOD sludge load is a condition of less than 0.15 kg-BOD / kg-VSS / day.

  (4) The method for treating organic wastewater according to any one of (1) to (3), wherein the flocculant has biodegradability.

  According to the present invention, in the membrane separation activated sludge method, troubles such as membrane permeability failure, foaming, scum generation and viscosity increase can be avoided continuously for a long time without increasing the amount of excess sludge generation. Processing becomes possible.

  Dispersible bacteria present in activated sludge, micronized floc, soluble microbial metabolite (SMP), extracellular polymer (EPS) peeled off floc, and other factors such as poor membrane permeability and foaming In qualitative, it is a sludge component that plays a central role, and when the concentration of these substances increases, the risk of trouble occurring increases, but according to the present invention, these substances are aggregated into flocs, Preferentially removes sludge components that adversely affect operation in the membrane-separated activated sludge process from the tank by preferentially preying the micro-animals on the portion where the components that cause sludge properties to deteriorate are densified. This makes it possible to effectively reduce the risk of driving trouble and greatly improve driving stability.

  In addition, even if a flocculant is added, it is decomposed by micro animals together with sludge components that adversely affect operation, so it does not increase the amount of excess sludge generated, and the added flocculant is decomposed. Has the advantage of avoiding problems such as inactivation of sludge due to the accumulation of the flocculant (which leads to an increase in the amount of excess sludge generated from the viewpoint of maintaining the treatment function) and a decrease in the effectiveness of the flocculant.

  In addition, by adding micro animals after adding flocculants, nitrifying bacteria and other slow-growing but useful bacteria are protected from predation of micro animals by a layer of sludge components and flocculants that adversely affect operation, and treated water quality Has the advantage that it is not impaired. In addition, by adding micro animals after adding the flocculant, dispersible bacteria, micro flocs, SMP, and exfoliated EPS are aggregated into the flocs, so that oxygen solubility is increased and a suitable environment for the growth of micro animals is prepared. Thus, a minute animal can be allowed to act in the environment, and the efficiency is improved from the viewpoint of utilization of the minute animal.

  In this way, the present invention fundamentally improves the operational stability in the treatment of organic wastewater, so it is more stable even when performing special operations such as longer sludge residence time and lower sludge load. Therefore, it is possible to further strengthen the function of suppressing the generation of excess sludge originally possessed by the membrane separation activated sludge method, and to further reduce the amount of generation of excess sludge.

  Note that the present invention is particularly effective for application to sugar-containing wastewater because there is a high risk of trouble occurring in sugar-containing wastewater regardless of the degree of solubility in water.

  Hereinafter, the present invention will be described in detail and specifically.

  In the present invention, organic wastewater such as wastewater is treated with, for example, the treatment apparatus shown in FIG. 1, and soluble organic substances (dissolved in water) contained in the finally obtained clarified liquid. The organic matter shown) is decomposed to such an extent that it can be discharged into a river or the like as it is. Here, the organic wastewater treated by the treatment method of the present invention includes industrial wastewater and domestic wastewater, and can be more suitably used for industrial wastewater discharged from food factories and the like. Moreover, it can use more suitably with respect to the organic waste water which has a polysaccharide as a main component.

  The processing apparatus shown in FIG. 1 performs solid-liquid separation on a biological reaction tank 1 containing activated sludge containing microorganisms, a raw liquid supply pump 4 that supplies the raw liquid to the biological reaction tank 1, and a biologically processed processing liquid. A membrane separation device 2, a suction pump 3 that sucks a separation liquid during solid-liquid separation, a micro animal storage tank 8, a micro animal supply pump 10, a coagulant storage tank 7, and a coagulant supply pump 11 are provided. ing. The membrane separation device 2 is immersed in a treatment liquid in the biological reaction tank 1, and oxygen is supplied below the membrane separation device 2 to advance the aerobic treatment and to perform the cleaning of the membrane surface. An aeration device 5 connected to 6 is provided. In addition, a sludge extraction pump 9 that extracts excess sludge is installed below the biological reaction tank 1. Even if the membrane separation device 2 is provided as a dedicated tank for solid-liquid separation separately from another biological treatment tank, for example, an anaerobic tank, an anaerobic tank, an aerobic treatment tank equipped with a fine bubble generator, and the like. good.

  The biological reaction tank 1 contains activated sludge containing microorganisms, and these microorganisms act as organic matter-degrading bacteria, and further, the organic matter-degrading bacteria act as microorganism-degrading bacteria to perform biological treatment. Therefore, it is preferable that the biological reaction tank 1 has no corners or irregularities on the inner surface so that sludge is not partially unevenly distributed. As a result, the temperature and pH of the treatment liquid become uniform in the biological reaction tank 1.

  Microorganisms contained in activated sludge contribute to the degradation of soluble organic matter such as bacteria, yeasts and fungi including fungi. Acquired from nature, such as soil, compost, and sludge, by accumulating culture and acclimatization Is done. It is also possible to isolate and use the main microbial group involved in the degradation from this conditioned solution.

  The biological reaction tank 1 must contain other components necessary for the growth of microorganisms. Therefore, for example, nitrogen, phosphorus, potassium, sodium, magnesium and other metal salts are added to the bioreactor, except when already contained in the stock solution.

  As the membrane separation device 2 provided in the biological reaction tank 1, a module formed using a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, a reverse osmosis membrane, or the like can be used. From the economical point of view, a module using a microfiltration membrane or an ultrafiltration membrane that has a high filtration rate and can be made compact and is easy to maintain is preferable. The membrane may be a flat membrane, a hollow fiber membrane or the like. The form of the module is not particularly limited, but in this embodiment, an immersion type membrane module is used for space saving. In the case of the immersion type, the shape is preferably such that the fouling substance can be successfully removed by combination and arrangement with an aeration apparatus or a stirring apparatus. Furthermore, as a filtration method in the membrane separation device 2, there are a cross flow method and a total amount filtration method. If the cross flow method is employed, filtration can be performed while removing the membrane surface.

  Means for causing a micro animal to act include a culture tank for a micro animal and a device for adding the culture solution in the culture tank to the aeration tank, a storage tank for the micro animal and a device for adding the liquid in the storage tank to the aeration tank, Necessary to circulate the liquid contained in the tank that soaked the carrier and the like to dominate the micro animal, the liquid contained in the tank that soaked the carrier etc. and made the micro animal dominant. Examples of the apparatus include pumps and piping. In addition, for the purpose of enhancing the action of the minute animal, a growth aid for the minute animal may be added. In addition, the enhancement of the action of the microanimal here means the addition of other microanimals, an increase in the circulating fluid flow rate of sludge between the microanimal treatment tank and the other organism treatment tank, and a suitable operating environment for the microanimal. Changes, and the introduction of a carrier that serves as a scaffold for the growth of small animals.

  The position of adding the flocculant is not particularly limited, but it is effective to have the highest concentration of dispersible bacteria, micro flocs, SMP, peeled EPS, and the added flocculant is well mixed with the sludge liquid. Although an aeration tank is suitable, it may be added to a place where the flocculant is finally mixed with activated sludge, such as a pipe for supplying wastewater or a denitrification tank.

  The flocculant used in the present invention may be cationic, nonionic, or anionic, as long as it has the ability to aggregate dispersible bacteria, micronized floc, SMP, peeled EPS, etc. to floc with an appropriate strength. A polymer flocculant can be used as appropriate, but a cationic polymer flocculant is most suitable in that it has the highest effect per added amount of the drug. In addition, in view of the affinity of the components that cause the sludge properties of the micro-animals to deteriorate and the environmental influences, those having biodegradability are suitable. In addition, the biodegradability said here means the property that it can be decomposed | disassembled to the component which has water and a carbon dioxide as a main component with the microorganisms which exist in nature.

  The amount of the flocculant used depends on the properties of the sludge to be treated, but is preferably 0.1 to 5% with respect to the MLSS concentration of the sludge. If the amount of the flocculant is too small, the cohesive force is insufficient and the effect is not exhibited. On the other hand, when an excessive amount of the flocculant is added, there is no change in the cohesive force, or there is a case where the coagulant is deteriorated. The optimum amount of flocculant is determined by adding a series of flocculants to sludge liquid in a simple jar test, filterability using filter paper, sedimentation of the liquid after addition, or total organic carbon in the centrifugal supernatant ( TOC) concentration, COD concentration, etc., and the amount of addition required for the amount of filtrate to be 15 ml or more when 50 ml of sludge is filtered for 5 minutes, the total organic carbon concentration of sedimentation or centrifugation supernatant, What is necessary is just to add in the ratio equivalent to the addition amount required for COD density | concentration becoming the minimum.

  The timing of adding the flocculant may be added based on the measurement results of the differential pressure and viscosity of the membrane, the increase in sludge concentration, the observation of foaming, and the supernatant TOC concentration, or at regular intervals without depending on the monitoring items. May be added.

  The microanimal is a protozoan such as a flagellate, a ciliate, or a fleshworm, or a minute metazoan including a bag-shaped animal or an annelid, and refers to an organism having a body length of 10 mm or less.

  The microanimal used in the present invention is not particularly limited as long as it is excellent in the predatory function of the sludge property deterioration causative component, but a metazoan that is mainly non-filtered and predatory is suitable. Here, the filter predatory property means that water flows around the cell's mouth due to the movement of cilia adhering to the vicinity of the cell's mouth, and the bacteria accompanying the water flow are taken into the body and filtered to eat the bacteria. Different from non-filtering predatory properties, it refers to the property of preying on bacteria so as to bite, and examples thereof include bag-shaped animals, mollusks, annelids, and slow-walking animals. In particular, nematodes and the like can be exemplified as the minute animals having high effects. Metazoans means animals composed of multiple cells, the main means that there are more non-filtered and predatory animals than filtered and predatory animals, It means that there are one or more kinds of animals.

  Regarding the timing of the operation A for adding the flocculant to the activated sludge and the operation B for causing the micro animal to act on the activated sludge, the operation B is performed between 3 days before and 7 days after the operation A. It is necessary to carry out at least once. If it is more than 3 days ago, filterability may deteriorate due to the addition of small animals. In addition, if 7 days or more have elapsed after the addition of the flocculant, the agglomeration force may be reduced and may not be efficient. More preferably, the operation B is performed at least once during the period from the first day to the third day after the operation A.

  If the present invention is applied, the present invention can fundamentally improve the operation stability in the treatment of organic wastewater, so when performing a special operation such as increasing the sludge residence time and lowering the sludge load. Therefore, it is possible to further enhance the surplus sludge generation suppressing function originally possessed by the membrane separation activated sludge method, and to further reduce the amount of surplus sludge generation. When aiming at such an effect, the present invention is preferably applied under the condition that the BOD sludge load is less than 0.15 kg-BOD / kg-VSS / day. The BOD sludge load is obtained by dividing the inflow amount of BOD supplied for wastewater treatment by the amount of sludge existing in all wastewater treatment tanks.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to an Example below. The evaluation was performed based on the following method.

[Evaluation of filter paper filterability]
The filter paper filterability was evaluated by measuring the amount of liquid when 50 ml of sludge liquid was filtered with a filter paper having a pore size of 0.1 micron for 5 minutes. Sludge having a liquid volume of 15 ml or more is judged to have good filterability.

[Measurement of MLSS concentration]
The MLSS concentration was measured by centrifuging as described in the Sewerage Test Method after collecting 1 ml of sludge sample.
(Example 1)
When a 30L membrane-separated activated sludge apparatus was used to treat a food factory simulated wastewater with a BOD concentration of 1,000 ppm under conditions of a water retention time of 1 day, the sludge filtration properties deteriorated when the MLSS concentration exceeded 13 g / L. The differential pressure began to rise rapidly. When 50 ml of sludge liquid at this time was filtered with 0.1 micron filter paper for 5 minutes, the liquid volume was about 3 ml.

  The sludge at this time was dispensed into four 700 ml small MBRs, and biodegradable flocculant (Flowac N, manufactured by Kyowa Technos Co., Ltd.) was added to one tank at a concentration of 0.2 g / L (B tank). In 1 tank, nematode-dominated microanimal culture solution (isolated from activated sludge with a stereomicroscope and cultured in E. coli) was added (C tank). Kyowa Technos Co., Ltd. Flownack N) was added at a concentration of 0.2 g / L, and a nematode dominant solution after 3 hours (liquid isolated from activated sludge with a stereomicroscope and cultured in Escherichia coli) Was added (D tank). When 4 series were operated in combination with 1 tank (A tank) to which nothing was added, the filter paper filterability was as shown in Table 1, sludge concentration.

It is the schematic which shows one embodiment of the processing apparatus used for the processing method of the organic wastewater of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Biological reaction tank 2 Membrane separation apparatus 3 Suction pump 4 Stock solution supply pump 5 Aeration apparatus 6 Blower 7 Coagulant storage tank 8 Micro animal storage tank 9 Sludge extraction pump 10 Micro animal supply pump 11 Coagulant supply pump 11

Claims (4)

In the treatment of organic wastewater by the membrane-separated activated sludge method including operation A for adding a flocculant to activated sludge and operation B for causing microanimals to act on activated sludge, operation B is performed on the 3rd day of operation A. A method for treating organic wastewater, which is carried out at least once between before and after 7 days. 2. The method for treating organic wastewater according to claim 1, wherein the micro animals are composed of a group of micro animals mainly composed of non-filtered predators. The organic wastewater treatment method according to claim 1 or 2, wherein the BOD sludge load is a condition of less than 0.15 kg-BOD / kg-VSS / day. The method for treating organic wastewater according to claim 1, wherein the flocculant has biodegradability.

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