JP2019181327A - Oil-containing wastewater treatment method - Google Patents

Abstract

An object of the present invention is to more easily treat wastewater containing a non-biodegradable water-soluble oil component. The present invention provides an oil-containing wastewater by a membrane separation activated sludge method using a treatment tank for biodegrading a water-soluble oil having biodegradability and a membrane separation tank for separating a water-insoluble oil by a membrane. The method relates to a method for treating oil-containing wastewater, wherein the sludge concentration (MLSS concentration) in the treatment tank at the start of the treatment is 10,000 mg / L or more, and the water temperature is 22 ° C. or more. The oil-containing wastewater of 1000 mg / L or less is passed through the treatment tank, the average sludge retention time (SRT) in the treatment tank is set to 40 days or more, and the average hydraulic retention time (HRT) in the treatment tank is set. ) Is set to 5 days or more and less than the average sludge residence time (SRT). [Selection] Figure 2

Description

  The present invention relates to an oil-containing wastewater treatment method.

  Due to growing interest in environmental issues, various technologies have been developed in the field of water treatment with the aim of preserving water quality and reducing environmental impact. One such technology is wastewater treatment technology for wastewater discharged to the environment.

  Various materials are contained in the wastewater depending on the type of facility that is the source of the wastewater, and it is important to perform wastewater treatment according to the contained materials. For example, the following treatment techniques have conventionally been proposed as wastewater treatment for wastewater containing oil (hereinafter also referred to as “oil-containing wastewater”).

  For example, Patent Document 1 below proposes a separation membrane module using a material optimal for oil separation as a technique for removing water-insoluble oil contained in oil-containing wastewater.

  As a technique for separating and removing the water-soluble oil contained in the oil-containing wastewater, as proposed in Patent Document 2 below, a membrane-separated activated sludge method is used, and a biochemical oxygen demand (Biochemical Oxygen Demand: BOD) is used. There is a technology that makes it possible to treat water-insoluble oils and water-soluble oils by appropriately performing biodegradability evaluation and optimal BOD sludge loading.

  Patent Document 3 below uses special microorganisms obtained by, for example, isolating and culturing microorganisms that live in oil-containing wastewater, and reproduces the conditions under which these special microorganisms become active. Thus, a technique for stably treating oil-containing wastewater containing water-soluble oil has been proposed.

  Patent Document 4 below discloses that a high-concentration oil-containing wastewater containing a water-insoluble oil component having bioinhibitory properties is obtained by microbially decomposing a water-soluble oil component having biodegradability and a non-biodegradable water-soluble oil component. A membrane separation activated sludge method has been proposed in which the sludge is adsorbed on the sludge and discharged out of the treatment tank, and the water-insoluble oil component is separated by a membrane in one treatment tank.

  Patent Document 5 below proposes a method in which oil-containing wastewater is treated aerobically with bacteria in the substantial absence of protozoa and then treated in an activated sludge tank.

  Further, in Patent Document 6 below, there is a method for suppressing clogging of the membrane by holding the inflowing oil in the membrane separation activated sludge tank due to the sludge adsorption effect and controlling so that X <(HRT / SRT) Y. Proposed. Here, in the above relational expression, X is the inflow oil concentration, Y is the retained oil concentration, HRT is the hydraulic residence time, and SRT is the sludge residence time.

International Publication No. 2011/101961 JP 2011-177608 A JP 2000-271589 A JP 2017-70894 A JP 2014-140795 A JP 2011-177607 A

  However, since the technique proposed in Patent Document 1 is a technique for removing the water-insoluble oil from the oil-containing wastewater using physical treatment, the water-soluble oil contained in the oil-containing wastewater cannot be separated and removed. .

  Moreover, the technique proposed in the above-mentioned Patent Document 2 is such that the readily biodegradable oil content in the oil-containing wastewater is about 300 mg / L, or the low biodegradable oil content is about 30 mg / L, and the concentration of the water-soluble oil component is This is a treatment method when the concentration is low. In a high concentration region above the above concentration, the oil-containing wastewater exhibits bioinhibition and reduces the activity of the activated sludge in the biological reaction tank. End up. For this reason, steps such as dilution and pretreatment are required, which is inefficient.

  Moreover, in the technique proposed in the above-mentioned Patent Document 3, it is necessary to isolate and culture special microorganisms for each drainage, which requires enormous time and cost and reduces the amount of treated water, which is inefficient. There is a problem that it is.

  Moreover, it is necessary to dispose after the technique proposed by the said patent documents 4 and 6 discharged | emitted the sludge which made water-soluble oil component adsorb | suck out of a processing tank.

  Moreover, the technique proposed in the above-mentioned Patent Document 5 requires a bacteria tank to be provided upstream of the activated sludge tank, which complicates the process.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to more easily treat waste water containing a non-biodegradable water-soluble oil component. The object is to provide an oil-containing wastewater treatment method.

  In order to solve the above problems, according to one aspect of the present invention, a treatment tank for microbial decomposition of a water-soluble oil component having biodegradability and a membrane separation tank for separating a water-insoluble oil component by a membrane are used. An oil-containing wastewater treatment method for treating oil-containing wastewater by a membrane separation activated sludge method, wherein the sludge concentration (MLSS concentration) in the treatment tank at the start of treatment is 10,000 mg / L or more, and the water temperature is 22 ° C or more. After that, the oil-containing wastewater having a water-soluble oil concentration of 1000 mg / L or less is passed through the treatment tank, and an average sludge residence time (SRT) in the treatment tank is set to 40 days or more. An oil-containing wastewater treatment method is provided in which the average hydraulic residence time (HRT) is 5 days or more and less than the average sludge residence time (SRT).

  In the oil-containing wastewater treatment method, the average sludge residence time (SRT) is in the range of 40 days to 120 days, and the average hydraulic residence time (HRT) is in the range of 5 days to 7 days. It is preferable to do.

  As described above, according to the present invention, wastewater containing a non-biodegradable water-soluble oil can be more easily treated.

It is explanatory drawing which showed typically an example of the structure of the oil-containing wastewater treatment apparatus which concerns on embodiment of this invention. It is the flowchart which showed an example of the flow of the oil-containing wastewater treatment method which concerns on the same embodiment. It is the graph which showed transition of the COD removal rate in a test example.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

(About the definition of organic substances in oil-containing wastewater)
The organic substance components present in the oil-containing wastewater can be roughly classified into four from the viewpoint of water insolubility / water solubility and from the viewpoint of non-biodegradability / biodegradability. Here, water-insoluble is a property with high hydrophobicity that forms an oil film when mixed with water, and water-soluble is a property with high hydrophilicity that mixes uniformly with water. . Further, non-biodegradable is a property that is difficult to be metabolized by microorganisms, and biodegradable is a property that is easily metabolized by microorganisms.

  In the technique disclosed in Patent Document 4, the water-insoluble oil component is separated by membrane separation, and the biodegradable oil component of the water-soluble oil component is treated with microorganisms. However, Patent Document 4 describes that the non-biodegradable oil is adsorbed by sludge and discharged out of the system.

  However, as a result of intensive studies on the organic components in the oil-containing wastewater roughly classified into the above four, the present inventors have found that, among the water-soluble oil components, the above-mentioned Patent Document 4 discharges out of the system. It has been found for the first time that even oils that have been made biodegradable can be decomposed by metabolism by microorganisms by setting the average hydraulic retention time (HRT) to 5 days or longer. According to such knowledge, while water-insoluble oil is separated by membrane separation, water-soluble oil can be decomposed by metabolism by microorganisms together with water-soluble oil that was originally biodegradable. Become. That is, according to the said knowledge, it becomes possible to process oil-containing wastewater more simply using the membrane separation activated sludge method including the oil component which was originally discharged | emitted with sludge outside. As a result of further studies based on such knowledge, the present inventors have come up with an oil-containing wastewater treatment method according to an embodiment of the present invention as described in detail below.

  Here, in the embodiment of the present invention, the average hydraulic residence time (HRT), which is an important factor, is a factor that affects the width of the wastewater treatment facility, and the average hydraulic residence time (HRT) is calculated as follows. Increasing the length means widening the wastewater treatment facility. For this reason, in general wastewater treatment technology, technical development has been conducted focusing on how to shorten the average hydraulic residence time (HRT), and the average hydraulic residence time (HRT) is In many cases, the estimated time is about 30 hours. On the other hand, the membrane separation activated sludge method utilized in the embodiment of the present invention is a method used for downsizing the wastewater treatment facility. Therefore, the operation of increasing the average hydraulic residence time (HRT) while adopting the membrane separation activated sludge method, as performed in the embodiment of the present invention, reduces the size of the waste water treatment facility, It should be noted that this is not an operation generally performed in wastewater treatment technology because it considers expansion of treatment facilities.

(About the configuration of oil-containing wastewater treatment equipment)
Below, before describing the oil-containing wastewater treatment method according to the embodiment of the present invention, the oil-containing wastewater treatment device used in the oil-containing wastewater treatment method according to the present embodiment will be briefly described with reference to FIG. To do. FIG. 1 is an explanatory view schematically showing an example of the configuration of the oil-containing wastewater treatment apparatus according to the present embodiment.

  As shown in FIG. 1, the oil-containing wastewater treatment apparatus 10 according to the present embodiment mainly includes a treatment tank 101, an aeration apparatus 103, a membrane filtration apparatus 105, a suction pump 107, and a waste mud valve 109. Prepare.

  The treatment tank 101 is a tank that functions as a biological reaction tank / membrane separation water tank in the membrane separation activated sludge method in the oil-containing wastewater treatment apparatus 10 according to the present embodiment. The size of the treatment tank 101 is not particularly limited, and may be set as appropriate according to the amount of oil-containing wastewater to be treated using the treatment tank 101. General sludge (for example, sewage sludge etc.) is held inside the treatment tank 101, and the organic matter (organic matter including the oil component targeted by the present application) in the waste water is decomposed in the sludge. There are various microorganisms such as microorganisms.

  The oil-containing wastewater to be treated by the oil-containing wastewater treatment method according to this embodiment is passed through the treatment tank 101 and is microbially decomposed by microorganisms present in the treatment tank 101.

  An aeration apparatus 103 is provided at the bottom of the processing tank 101, for example. The aeration apparatus 103 supplies oxygen to the sludge retained in the treatment tank 101, thereby supplying oxygen necessary for the growth of microorganisms present in the sludge, and a membrane filtration apparatus 105 described later. Prevents sludge from adhering to the separation membrane surface.

  As the aeration apparatus 103, a known apparatus can be used. Further, the amount of oxygen supplied from the aeration apparatus 103 is not particularly limited, and the general oxygen amount necessary for the growth of microorganisms without sludge being deposited on the membrane surface of the membrane filtration device 105 described later. What is necessary is just to supply. As such an oxygen amount, for example, an oxygen amount such that a dissolved oxygen amount (DO) is 0.1 mg / L or more can be exemplified.

  In the oil-containing wastewater treatment apparatus according to the present embodiment, microbial decomposition of water-soluble oil by microorganisms in sludge is promoted by oxygen supplied from the aeration apparatus 103. Thereby, the water-soluble oil which has biodegradability among oil-containing wastewater is decomposed | disassembled by activated sludge.

  In Patent Document 4, water-soluble oil (non-biodegradable oil) that does not have biodegradability among oil-containing wastewater is adsorbed to activated sludge without being decomposed by activated sludge, and a drainage valve 109 described later. Has been proposed to discharge from the processing tank 101 together with sludge. However, in the technique disclosed in Patent Document 4, the non-biodegradable oil remains in the treatment tank as the time until sludge is extracted (average sludge retention time: SRT) increases. Therefore, there is a limit to the longer SRT time that is preferable for activating microorganisms.

  On the other hand, as a result of intensive studies, the present inventors have increased the average hydraulic residence time (HRT) to 5 days or more as will be described in detail below. It has been found that it is possible to remove the characteristic oil. When a certain amount of wastewater is generated, it is necessary to increase the volume of the treatment tank 101 in order to lengthen the average hydraulic residence time (HRT), but the membrane separation activated sludge method is better than the standard activated sludge method. Since the equipment can be downsized, there is an advantage of adopting the membrane separation activated sludge method even when the average hydraulic residence time (HRT) is extended, and it is also advantageous when there is a site restriction. By implementing the oil-containing wastewater treatment method according to this embodiment described in detail below, even oil that has been considered to be non-biodegradable among water-soluble oils can be decomposed by activated sludge. It becomes possible.

  A membrane filtration device 105 is disposed above the aeration device 103 disposed in the treatment tank 101. The membrane filtration device 105 is a device for solid-liquid separation of wastewater that has entered the membrane filtration device 105. A separation membrane that allows the treated water from which oil has been removed to pass through is provided on the surface and inside of the membrane filtration device 105. Treated water in which water-soluble oil (biodegradable and non-biodegradable) has been decomposed by microorganisms from oil-containing wastewater by suction-filtering the inside of the membrane filtration device 105 with a suction pump 107 connected to the membrane filtration device 105 However, it will be discharged | emitted out of the processing tank 101. FIG.

  Here, the separation membrane provided in the membrane filtration device 105 is not particularly limited, and various known microfiltration membranes having shapes such as a flat membrane and a hollow fiber membrane can be used. Specific examples of the porous membrane used as a material for such a separation membrane include, for example, a polyacrylonitrile porous membrane, a polyimide porous membrane, a polyethersulfone porous membrane, a polyphenylene sulfide sulfone porous membrane, and a polytetrafluoroethylene porous membrane. Examples thereof include a porous membrane, a polyvinylidene fluoride porous membrane, a polypropylene porous membrane, and a polyethylene porous membrane. In addition, for these porous membranes, it is also possible to use composite membranes in which rubbery polymers such as cross-linked silicone, polybutadiene, polyacrylonitrile butadiene, ethylene propylene rubber, and neoprene rubber are combined as functional layers. is there.

  Moreover, what is necessary is just to set suitably the flow volume which the processing tank 101 does not overflow according to the magnitude | size of the processing tank 101, as the flow volume of the oil-containing wastewater passed through the processing tank 101. A flow rate adjusting tank for cutting out a fixed amount of oil-containing waste water and passing it to the processing tank 101 is provided in the previous stage of the processing tank 101 so that oil-containing waste water having a constant flow rate is continuously passed through the processing tank 101. Also good.

  Heretofore, the configuration of the oil-containing wastewater treatment apparatus used in the oil-containing wastewater treatment method according to the present embodiment has been described in detail with reference to FIG.

(About oil-containing wastewater treatment methods)
Next, the oil-containing wastewater treatment method according to the embodiment of the present invention will be described in detail with reference to FIG.

<Details of the study conducted by the present inventors>
The present inventors have intensively studied for the purpose of draining oil-containing wastewater having a water-soluble oil concentration of 1000 mg / L or less using a membrane separation activated sludge method.

  In the above-mentioned Patent Document 4, by increasing the average sludge residence time (SRT) in the treatment tank 101, the time required for the sludge-derived microorganisms to grow by the oil-containing wastewater is ensured and propagated to increase the activity of the activated sludge. A method of ensuring is disclosed. Here, in the method disclosed in Patent Document 4, the water-soluble non-biodegradable oil contained in the oil-containing wastewater is discharged out of the treatment tank 101 by being adsorbed by the sludge and extracted.

  On the other hand, when the sludge concentration (Mixed Liquor Suspended Solids: MLSS concentration) is high, the inventors of the present invention can reduce the activity of the activated sludge to a certain level, but further, the sludge concentration in the treatment tank 101 It was thought that by prolonging the time (HRT), it would be possible to decompose oil that had been considered to be non-biodegradable, which was difficult to decompose by microorganisms. In other words, by maintaining a high sludge concentration (MLSS concentration) and prolonging the hydraulic residence time (HRT), oil that has been considered to be non-biodegradable in the past is not easily decomposed, but microorganisms I thought that it could be redefined as an oil that can be decomposed by (so to speak, a non-biodegradable oil).

  The idea is that (a) the MLSS concentration can be maintained at a high level by the oil-containing wastewater treatment apparatus using the membrane separation activated sludge method, and the outflow of sludge can be suppressed as compared with the standard activated sludge method, and (b) average The sludge is retained in the treatment tank 101 by extending the sludge residence time (SRT), so that the microbial flora is very diverse and retains microorganisms capable of decomposing oil that has been considered non-biodegradable. It is because of having thought that there is a possibility that it has been.

  Furthermore, if microorganisms as described above are present, the conventional standard activated sludge method is difficult to grow in the treatment tank 101, so the growth rate is assumed to be slow, so the decomposition rate is also assumed to be slow. It was. Therefore, (c) by increasing the hydraulic residence time in the treatment tank 101 (HRT, in other words, the treatment time of microorganisms), the treatment time by the sludge-derived microorganisms is ensured and non-biodegradable. This is because it was thought that the oil component that was said to be capable of being decomposed as a non-biodegradable oil component.

  Based on the above idea, as a result of investigations based on experiments by the present inventors, adjustment of sludge concentration in the treatment tank 101 at the start of treatment as described above, average sludge residence time in the treatment tank 101 In addition to the prolonged (SRT), it was newly found that the average hydraulic residence time (HRT) should be prolonged. Below, the non-biodegradable oil part in the said patent document 4 is redefined as a hardly biodegradable oil part.

  In addition, regarding the content that the oil-containing wastewater is treated with a relatively long average hydraulic residence time (HRT), the example of Patent Document 6 describes that the average hydraulic residence time (HRT) = 3.5 days. ing. Therefore, hereinafter, the difference between the present technology based on the idea of the present inventors and the technology disclosed in Patent Document 6 will be briefly described.

  The above-mentioned patent document 6 is based on the premise that oil is removed by adsorbing oil to sludge and extracting the sludge, and using the inflow oil concentration X and the retained oil concentration Y, the average hydraulic retention The ratio between time (HRT) and average sludge residence time (SRT) is defined as X <(HRT / SRT) Y. The above equation can be converted as (SRT / HRT) <(Y / X). However, in this embodiment, since the oil is decomposed by microorganisms, X> Y, so (SRT / HRT) <(Y / X) <1. From this, the relationship SRT <HRT is obtained. Here, from the definitions of average hydraulic residence time (HRT) and average sludge residence time (SRT), the above relationship SRT <HRT means that the inflow water amount is less than the sludge extraction flow rate. As a result, it means that the waste water treatment of “the waste water that has flowed into the treatment tank 101 is merely extracted” is performed. However, the present technology based on the idea of the present inventors does not perform a process of simply extracting the waste water flowing into the treatment tank 101, and the present technology based on the idea of the present inventors and the above-mentioned Patent Document 6 It is different from the disclosed technology. Moreover, even if the relational expression disclosed in Patent Document 6 is applied to the oil-containing wastewater treatment method according to the present embodiment, which will be described in detail below, the hardly biodegradable oil component cannot be decomposed.

<Details of oil-containing wastewater treatment method>
Hereinafter, the oil-containing wastewater treatment method according to the present embodiment based on the idea of the present inventors will be described in detail.

  First, in this embodiment, the water-soluble oil concentration of the oil-containing wastewater to which attention is paid can be specified as follows. The analysis method is a known method (for example, a method defined in JIS K0102 “Factory wastewater test method”). First, the amount of n-hexane extract contained in the oil-containing wastewater is measured by a known method. The concentration of suspended solids (SS) contained in the same oil-containing wastewater is measured by a known method. Since the SS component contained in the oil-containing wastewater can be regarded as a substantially water-insoluble oil, the value obtained by subtracting the SS concentration from the n-hexane extract amount can be handled as the water-soluble oil concentration of the oil-containing wastewater.

  That is, in this embodiment, the amount of the n-hexane extract corresponds to the total amount of oil contained in the oil-containing wastewater, and the water-insoluble oil contained in the oil-containing wastewater is extracted as a suspended substance. it is conceivable that. Therefore, it becomes possible to obtain the water-soluble oil concentration in the oil-containing wastewater by subtracting the SS concentration from the n-hexane extract amount. As an index that can replace the water-soluble oil concentration, for example, a chemical oxygen demand (CODMn) measured by a known method can be cited. By using the chemical oxygen demand (CODMn) instead of the water-soluble oil concentration, it is possible to more easily measure the concentration corresponding to the water-soluble oil concentration.

In addition, the “average sludge residence time (SRT)” focused on in the present embodiment is the capacity [unit: m ³ ] of the treatment tank 101 as shown in FIG. 1 and the sludge extraction flow rate [unit: m ³ / day]. ], And “average hydraulic residence time (HRT)” means the capacity [unit: m ³ ] of the treatment tank 101 as shown in FIG. Unit: m ³ / day].

  The oil-containing wastewater treatment method according to the present embodiment, which has been completed based on the above-described knowledge, is based on a membrane separation activated sludge method in which oil-containing wastewater is microbially decomposed and solid-liquid separation of sludge by the membrane and treated water is performed. This is an oil-containing wastewater treatment method.

  In the oil-containing wastewater treatment method according to the present embodiment, the sludge concentration (MLSS) in the treatment tank 101 at the start of treatment is 10000 mg / L or more, and the water temperature is 22 ° C. or more. Thereafter, oil-containing wastewater having a water-soluble oil concentration of 1000 mg / L or less is passed through the treatment tank 101, the average sludge residence time (SRT) in the treatment tank 101 is set to 40 days or more, and the average hydraulic The residence time (HRT) is 5 days or longer and less than the average sludge residence time (SRT). By performing such treatment, not only biodegradable water-soluble oils but also hardly biodegradable water-soluble oils can be treated more efficiently, simply and stably without using special seed sludge or chemicals. It becomes possible to do.

  Here, in the oil-containing wastewater treatment method according to the present embodiment, the oil-containing wastewater treatment apparatus 10 as shown in FIG. 1 is used, but general sewage sludge is retained inside the treatment tank 101 as activated sludge. It is assumed that At this time, the temperature (water temperature) of the sewage sludge retained in the treatment tank 101 is set to 22 ° C. or higher as described above. When the temperature (water temperature) of the sewage sludge held in the treatment tank 101 is less than 22 ° C., the processability of the oil-containing wastewater is lowered. On the other hand, the upper limit of the temperature (water temperature) of the sewage sludge held in the treatment tank 101 is not particularly specified, but if the water temperature becomes too high, the activity of microorganisms may be reduced. Therefore, it is preferable that the temperature (water temperature) of the sewage sludge currently hold | maintained at the processing tank 101 shall be 30 degrees C or less, for example.

  In addition, the temperature (water temperature) of the oil-containing wastewater passed through the treatment tank 101 may be set to 22 ° C. or higher so as not to lower the temperature of the sewage sludge held in the treatment tank 101 more than necessary. preferable. When the water temperature of the oil-containing wastewater passed through the treatment tank 101 is less than 22 ° C., it is preferable to heat using a heater or the like.

  In the oil-containing wastewater treatment method according to the present embodiment, as shown in FIG. 2, the sludge concentration in the treatment tank 101 is adjusted prior to passing the oil-containing wastewater into the treatment tank 101 (step S101). Specifically, the sludge present in the treatment tank 101 is concentrated as necessary so that the sludge concentration (MLSS concentration) in the treatment tank 101 at the start of the treatment is 10,000 mg / L or more.

  Here, when the sludge concentration at the start of treatment (MLSS concentration) is less than 10000 mg / L, when the oil-containing wastewater having a high water-soluble oil concentration is passed through the treatment tank 101, the activated sludge activity The reduction of the oil becomes remarkable, and the oil-containing wastewater cannot be treated efficiently. On the other hand, if the sludge concentration at the start of treatment (MLSS concentration) is 10000 mg / L or more, even if the activity of the activated sludge is temporarily reduced when oil-containing wastewater having a high water-soluble oil concentration is passed, By setting an average sludge residence time (SRT) to be described later in an appropriate range, it becomes possible to recover the activity of the activated sludge. As a result, even when oil-containing wastewater having a high water-soluble oil concentration is passed, such oil-containing wastewater can be treated. In addition, the sludge density | concentration (MLSS density | concentration) at the time of a process start is 10000 mg / L or more, so that it is so good that it is high, and the upper limit in particular is not prescribed | regulated.

  In the oil-containing wastewater treatment method according to the present embodiment, after the sludge concentration (MLSS concentration) in the treatment tank 101 reaches 10,000 mg / L or more, the oil-containing wastewater containing the water-soluble oil concentration is continuously fed into the treatment tank 101. (Step S103). The water-soluble oil concentration may be in any range, and when the water-soluble oil concentration is low, the treatment can naturally be performed, but even a high concentration is effective. The water-soluble oil concentration of the oil-containing wastewater continuously passed through the treatment tank 101 is preferably 400 to 1000 mg / L.

  In the oil-containing wastewater treatment method according to the present embodiment, when the oil-containing wastewater is continuously passed through the treatment tank 101, the average hydraulic residence time (HRT) of the treatment tank 101 is 5 days or more. The amount of water flowing into the treatment tank 101 is controlled so as to be less than the residence time (SRT).

  Here, when the average hydraulic residence time (HRT) of the treatment tank 101 is less than 5 days, the treatment time is too short, so that the hardly biodegradable oil in the oil-containing wastewater passed through is sufficiently decomposed. The oil-containing wastewater cannot be treated efficiently. On the other hand, by setting the average hydraulic residence time (HRT) to 5 days or longer and less than the average sludge residence time (SRT), the content of the non-biodegradable oil by microorganisms in the oil-containing wastewater acclimatized and maintained by the membrane separation activated sludge device A sufficient decomposition time can be secured, and the oil content in the oil-containing wastewater can be decomposed.

  In addition, about the substantial upper limit of the average sludge residence time (HRT) in the processing tank 101, if the value will be less than an average sludge residence time (SRT), it will not prescribe | regulate and it will affect site restrictions. The longer it is, the better. As such an average hydraulic residence time (HRT), for example, a period of about 5 to 7 days is preferably set.

  After the oil-containing wastewater is passed into the treatment tank 101, oxygen necessary for microbial growth is supplied using the aeration apparatus 103 to promote microbial decomposition of the water-soluble oil and supplied from the aeration apparatus 103. Oxygen is used to remove the membrane plugging material deposited on the membrane surface of the membrane filtration device 105. Thereby, the water-soluble oil component contained in the oil-containing wastewater is decomposed by microorganisms.

  In addition, the water-insoluble oil contained in the oil-containing wastewater is adsorbed by the activated sludge held in the treatment tank 101.

  In the membrane filtration device 105, the inside of the membrane filtration device 105 is continuously sucked by the suction pump 107, and sludge and microorganisms are separated from the treated water by the separation membrane of the membrane filtration device 105. As a result, the treated water from which these oils have been removed is discharged out of the system.

  Here, in the oil-containing wastewater treatment method according to the present embodiment, the mud is discharged from the mud valve 109 so that the average sludge residence time (SRT) in the treatment tank 101 is 40 days or more (step) S105). By such waste mud, the oil component adsorbed by the sludge is discharged out of the system.

  When the average sludge residence time (SRT) is less than 40 days, the acclimatization time is too short, so that the microorganisms cannot be sufficiently propagated by the oil-containing wastewater that has been passed through. However, oil-containing wastewater cannot be treated efficiently. On the other hand, by setting the average sludge residence time (SRT) to 40 days or longer, microorganisms can be kept in the system for a long time and acclimatized with oil-containing wastewater, and can be grown. In addition, about the upper limit of the average sludge residence time (SRT) in the processing tank 101, it does not prescribe | regulate in particular, The range which does not influence the whole waste_water | drain processing is so good that it is long. As such an average sludge residence time (SRT), for example, a period of about 40 days to 120 days is preferably set.

  As described above, in the oil-containing wastewater treatment method according to the present embodiment, the sludge concentration (MLSS concentration) at the start of treatment is set to 10,000 mg / L or more, the water temperature is set to 22 ° C. or more, and the average sludge residence time (SRT) is set. 40 days or more and the average hydraulic residence time (HRT) is 5 days or more and less than the average sludge residence time (SRT). Thereby, in the oil-containing wastewater treatment method according to the present embodiment, the chemical oxygen demand (CODMn) and n-hexane extract of oil-containing wastewater can be stably treated without searching for special microorganisms and culturing. .

  Hereinafter, the oil-containing wastewater treatment method according to the present invention will be specifically described with reference to Examples and Comparative Examples. In addition, the Example shown below is an example to the last of the oil-containing wastewater treatment method which concerns on this invention, Comprising: The oil-containing wastewater treatment method which concerns on this invention is not limited to the following example.

In this test example, a treatment tank 101 having a capacity of 1.7 m ³ is prepared as the treatment tank 101 of the oil-containing wastewater treatment apparatus shown in FIG. 1, and the aeration apparatus 103 and the membrane filtration apparatus 105 are provided outside the treatment tank 101. Was installed.

  Such sewage sludge is injected into the inside of the treatment tank 101, and the sludge concentration (MLSS concentration) at the start of the treatment is 10,000 mg / L using the membrane filtration device 105 and the suction pump 107. Concentration was performed. The temperature of the sewage sludge was controlled to 23 to 29 ° C., and the average sludge residence time (SRT) was controlled to 40 days or more.

  The oil-containing wastewater discharged from the thin plate factory was used as the oil-containing wastewater passed through the treatment tank 101. In the thin plate factory, various lubricating oils are used for the steel sheet that is the original plate, and various oils are also used to cool the manufactured thin plate, and these oils are contained in the waste water. . The amount of COD and n-hexane extract contained in the oil-containing wastewater was measured based on JIS K 0102. CODMn was 2100-2900 mg / L, and the amount of n-hexane extract was 400-1000 mg / L. . Separately, the SS concentration of the oil-containing wastewater measured based on JIS K 0102 was 0 to 60 mg / L, and the water-soluble oil concentration of the target oil-containing wastewater was 400 to 1000 mg / L.

  Treatment of oil-containing wastewater (water temperature: 22-29 ° C.) having a water-soluble oil concentration as described above under conditions where the average hydraulic residence time (HRT) is 3.7 days and 5 days. Water was continuously passed through the tank 101. At this time, oxygen was supplied from the aeration apparatus so that the dissolved oxygen amount (DO) was 0.1 mg / L or more, and wastewater treatment was performed by the membrane separation activated sludge method.

  The obtained results are summarized in FIG. The water-soluble oil concentration is proportional to the CODMn concentration. In this test example, the CODMn concentration was used as an alternative index for the water-soluble oil concentration.

  As shown in FIG. 3, when the average hydraulic residence time (HRT) was set to 3.7 days, the CODMn removal rate at the start of the test was 31%, but only about 2 weeks. The test was stopped because it was reduced to about 10% and the deterioration of sludge properties was also confirmed by visual observation.

  On the other hand, when the average hydraulic residence time (HRT) was set to 5 days, the CODMn removal rate at the start of the test was 27%, but increased to 56% in 3 weeks, and then for 2 months. It became 70% after acclimatization, and a significant improvement effect was recognized. From another point of view, the treated water CODMn concentration in this test example means a decrease from 2000 mg / L to 870 mg / L, and if the amount of generated water is constant, nearly 60% of COD load is reduced. A great effect on water quality management was observed.

  As described above, it was found that by using the oil-containing wastewater treatment method according to the present invention, even wastewater containing a hardly biodegradable water-soluble oil can be treated more efficiently and easily. .

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

10 Oil-impregnated wastewater treatment equipment 101 Biological reaction tank and membrane separation water tank (treatment tank)
103 Aeration device 105 Membrane filtration device 107 Suction pump 109 Drain valve

Claims (2)

An oil-containing wastewater treatment method that treats oil-containing wastewater by a membrane separation activated sludge method using a treatment tank that microbially decomposes a water-soluble oil having biodegradability and a membrane separation tank that separates a water-insoluble oil with a membrane. There,
The sludge concentration (MLSS concentration) in the treatment tank at the start of treatment is set to 10,000 mg / L or more and the water temperature is set to 22 ° C. or more, and then the oil-containing wastewater having a water-soluble oil concentration of 1000 mg / L or less is treated. Water to the tank,
Oil-containing wastewater having an average sludge residence time (SRT) in the treatment tank of 40 days or more and an average hydraulic residence time (HRT) in the treatment tank of 5 days or more and less than the average sludge residence time (SRT) Processing method. The average sludge residence time (SRT) is in the range of 40 days to 120 days,
The oil-containing wastewater treatment method according to claim 1, wherein the average hydraulic residence time (HRT) is in a range of 5 days or more and 7 days or less.

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