JP2011177607A - Oil-containing waste water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an efficient oil-containing waste water treatment method which can effectively inhibit the clogging of a membrane caused by inflow oil and can stably operate a membrane separation activated sludge treatment tank by controlling the oil concentration so as to satisfy a fixed index in a process for performing membrane separation activated sludge treatment of oil-containing waste water. <P>SOLUTION: In the oil-containing waste water treatment method having a membrane separation activated sludge treatment process for biologically treating the oil-containing waste water in the activated sludge treatment tank and membrane separating the biologically treated water by a membrane separation device installed in an activated sludge treatment tank, at least one of oil concentration X flowing into the activated sludge treatment tank, a solid retention time SRT, a hydraulic retention time HRT, and retained oil concentration Y in the activated sludge treatment tank is controlled so that the oil concentration X, the concentration rate represented by SRT/HRT, and the retained oil concentration Y satisfies the following relation: X<(HRT/SRT)Y. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  In the present invention, wastewater containing oil, such as general sewage and industrial wastewater, is biologically treated in an activated sludge treatment tank, and then subjected to membrane separation treatment (hereinafter collectively referred to as “membrane separation activated sludge treatment”). Thus, it is a treatment method that can be suitably used when obtaining treated water.

  Conventionally, when wastewater containing oil is subjected to membrane separation activated sludge treatment, inflow oil concentration is reduced by pretreatment in order to stably operate and maintain the treatment tank. There are various types of oil contained in the wastewater, and the properties and contents differ, but as a general pretreatment, agglomeration separation treatment, pressurized flotation separation treatment, electrolytic treatment, and the like are performed. For example, in Patent Document 1, waste water containing organic solids such as fats and oils is separated into a solid content and a supernatant liquid in a solid-liquid separation tank in advance, and the solid content is solubilized at a high temperature, and then the supernatant liquid and the processing liquid are Biological treatment techniques have been proposed. Moreover, in patent document 2, the technique of carrying out the activated sludge process of the treated water which carried out the electrolytic treatment and the coagulation process of the waste water containing a hard-to-decompose oil and fat etc. is proposed.

  All of these are technologies related to pretreatment for reducing the inflow oil content in advance, and have a certain effect. However, since it is reduced uniformly regardless of the oil concentration, if the oil concentration is low, an excessive pretreatment facility is required, which causes a problem in terms of operating costs. In addition, after the start of operation, the activated sludge condition deteriorates, and when changing the pretreatment conditions according to the activated sludge tank condition and treatment capacity, the oil condition allowed in the membrane separation activated sludge treatment tank is unknown. As a result, it may result in improper operating conditions and clog the membrane.

  In this situation, it was known that the pretreatment should be strengthened and the inflow oil content should be reduced as much as possible. It was unclear whether the allowable range of oil concentration should be done.

  Therefore, it was necessary to clarify the allowable range (hereinafter referred to as “guideline”) for stable operation and maintenance of the membrane separation activated sludge treatment tank.

Japanese Patent No. 3900796 JP 2007-029825 A

  The present invention solves the above-mentioned problems and is based on a guideline for stable operation and maintenance of a membrane separation activated sludge treatment tank when oil-containing wastewater is treated with membrane separation activated sludge to obtain treated water. The present invention proposes an appropriate treatment method for oil-containing wastewater, and provides an efficient treatment method without clogging the membrane.

In order to solve the above problems, the present invention has the following configuration.
(1) Oil-containing wastewater having a membrane-separated activated sludge treatment process in which oil-containing wastewater is biologically treated in an activated sludge treatment tank, and the water that has been biologically treated by a membrane separator installed in the activated sludge treatment tank is membrane-separated. In the wastewater treatment method, the oil concentration X flowing into the activated sludge treatment tank, the concentration ratio represented by the ratio of solid residence time SRT and hydraulic residence time HRT (SRT / HRT ratio), in the activated sludge treatment tank Oil content is characterized in that at least one of oil concentration X, solid residence time SRT, hydraulic residence time HRT, and retained oil concentration Y is controlled so that the retained oil concentration Y satisfies the following relationship: Wastewater treatment method.

X <(HRT / SRT) Y
(2) A pretreatment step of pretreating oil-containing wastewater before the membrane separation activated sludge treatment step, the oil concentration X flowing into the activated sludge treatment tank, and the supernatant and sludge in the activated sludge in the tank And measuring at least one of the pretreatment process conditions and the membrane separation activated sludge tank operation conditions based on the measurement results (1) The processing method of oil-containing wastewater as described in 2.

  According to the present invention, in the process of solving the above-mentioned problems and treating the oil-containing wastewater with membrane separation activated sludge, by controlling the oil concentration and the like so as to satisfy a certain guideline, Clogging can be effectively suppressed, the membrane separation activated sludge treatment tank can be stably operated, and an efficient treatment method can be provided.

It is the schematic which shows an example of the water treatment apparatus used for the water treatment method of this invention.

  The treatment method according to the present invention is based on a certain standard in order to perform stable operation and maintenance without clogging the membrane when treating wastewater containing oil in the process of treating the water to be treated with membrane separation activated sludge. It is characterized by controlling the oil concentration flowing into the activated sludge tank so as to satisfy.

  As a result of intensive studies, the inventors have determined that the inflow oil content is blocked by the membrane in the membrane separation activated sludge tank, and is concentrated in the tank, and the synergistic effect of the effect that the oil content is adsorbed on the sludge. It has been found that the membrane is clogged when it is held inside and its holding concentration reaches the upper limit. The present invention is based on the knowledge obtained from the results, that is, the knowledge that stable operation and maintenance is possible by controlling the inflow oil concentration without reaching the upper limit of the retained oil concentration in the tank. is there.

  FIG. 1 outlines the steps of a general membrane separation activated sludge treatment apparatus used in the present invention. In the apparatus of FIG. 1, the membrane filtration apparatus 2 (henceforth abbreviated as MF membrane filtration apparatus 2) for filtering the to-be-processed water 1 with a microfiltration membrane, and obtaining this filtered water, and this MF membrane filtration apparatus 2 are used. Activated sludge treatment tank 3 for immersing in the mixed liquid of treated water 1 and activated sludge, and filtered water obtained by membrane filtration of the mixed liquid of treated water 1 and activated sludge using MF membrane filtration device 2 Is stored. The treated water 5 is reused or discharged as treated water.

  Below, the processing flow which shows the embodiment of the water treatment method of this invention is outlined.

  First, the treated water 1 containing oil is supplied into the activated sludge treatment tank 3, and the treated water is subjected to activated sludge treatment in the activated sludge treatment tank 3. The activated sludge introduced into the activated sludge treatment tank 3 is generally used for wastewater treatment and the like, and as the seed sludge, drawn sludge from other wastewater treatment facilities is usually used. The residence time in the activated sludge treatment tank 3 of the water to be treated is usually 1 hour to 24 hours, but it is preferable to select an optimum one according to the state of the water to be treated.

  Next, the water subjected to the activated sludge treatment in the activated sludge treatment tank 3 is filtered by the membrane separation device 2 in the same activated sludge treatment tank 3. The filtered water is stored in the filtered water tank 4.

  Here, the membrane filtration device 2 has, for example, a flat membrane element structure in which a filtration membrane is bonded to both sides of a frame with a filtration membrane attached to both sides of the frame in order to improve the handling and physical durability of the filtration membrane. It is desirable to be. The structure of the MF membrane filtration device 2 is not particularly limited and may be an element using a hollow fiber membrane, but the flat membrane element structure has a shearing force when a flow velocity parallel to the membrane surface is applied. This is suitable for the present invention since the effect of removing dirt due to is high. The flat membrane element structure includes a rotating flat membrane structure in which a flat membrane is wound in a spiral shape.

  Examples of the membrane structure of the filtration membrane used in the MF membrane filtration device 2 include a porous membrane and a composite membrane obtained by combining a functional layer with a porous membrane, but are not particularly limited. Specific examples of these membranes include polyacrylonitrile porous membrane, polyimide porous membrane, polyethersulfone porous membrane, polyphenylene sulfide sulfone porous membrane, polytetrafluoroethylene porous membrane, polyvinylidene fluoride porous membrane, polypropylene Examples of the porous film include a porous film and a porous film such as a polyethylene porous film, and a polyvinylidene fluoride porous film and a polytetrafluoroethylene porous film are particularly preferable because of high chemical resistance. Furthermore, a composite membrane in which a rubbery polymer such as a crosslinked silicone, polybutadiene, polyacrylonitrile butadiene, ethylene propylene rubber, or neoprene rubber is combined as a functional layer with these porous membranes can also be used as the MF filtration membrane 2.

  The microfiltration membrane (MF membrane) referred to here is one having a pore size of about 0.01 μm to 10 μm, and is generally coarser than an ultrafiltration membrane (UF membrane) in which separation by molecular sieve is generally performed. The operation pressure is operated at 200 kPa or less from the reduced pressure state.

  The activated sludge treatment tank 3 is not particularly limited as long as it can store the treated water and immerse the MF membrane filtration device 2 in the mixed liquid of the treated water and activated sludge. Concrete tank, fiber reinforced plastic tank, etc. Is preferably used. Moreover, the inside of the activated sludge treatment tank 3 may be divided into a plurality of parts, and a part of the plurality of divided tanks is used as a tank for immersing the membrane filtration device 2 and the other is used as a denitrification tank. The water to be treated may be circulated between the tanks that are divided from each other.

  The activated sludge introduced into the activated sludge treatment tank 3 is generally used for wastewater treatment and the like, and the sludge extracted from other wastewater treatment facilities is usually used as seed sludge. In the membrane separation activated sludge method, the operation is performed at a sludge concentration of about 2,000 mg / L to 20,000 mg / L. The activated sludge method makes it possible to purify water by using a highly biodegradable component in wastewater as a feed for microorganisms.

  The filtered water tank 4 is not particularly limited as long as the filtered water can be stored, and a concrete tank, a fiber reinforced plastic tank, and the like are preferably used. Moreover, in order to filter to-be-processed water with the MF membrane filtration apparatus 2, you may provide a pump etc. between the MF membrane filtration apparatus 2 and the filtration water tank 4, and in order to apply a head pressure difference, a filtration water tank The filtrate water level in 4 may be lower than the water level to be treated in the activated sludge treatment tank 3. In FIG. 1, filtration by the suction pump 9 is performed.

  Here, the oil contained in the water 1 to be treated is, for example, extracted from animals and plants, highly biodegradable oil composed of a compound of glycerin and fatty acid, obtained by petroleum refining, or produced by chemical synthesis. Examples include hardly-degradable mineral oils. The oil concentration measurement method is not particularly limited as long as the oil concentration can be quantified. For example, the n-hexane extract concentration measurement method described in the sewage test method (Japan Sewerage Association) Preferably used. Also, a commercially available oil concentration meter or oil concentration measurement kit may be used.

  Here, the n-hexane extract measuring method preferably used is to add n-hexane and an acid such as hydrochloric acid to the object containing oil, and stir to extract the oil into the n-hexane layer. After separating the oil component, only the oil layer is recovered and the weight after evaporation to dryness at 80 ° C. is measured.

  In the membrane separation activated sludge method, the substance flowing into the activated sludge treatment tank 3 is usually mixed with the activated sludge, and the highly biodegradable substance is biodegraded by microorganisms in the activated sludge. On the other hand, the hardly decomposable substance is concentrated in the tank until it is extracted as excess sludge together with the activated sludge. In this case, the concentration rate represents the rate at which the inflowed substance is concentrated and accumulated in the tank, and the rate (concentration rate = reaction tank concentration / inflow water concentration) is theoretically SRT (solid matter residence time). It corresponds to the ratio of SRT / HRT (hydraulic residence time) (SRT / HRT ratio) and is expressed by the following relational expression (formula 1).

Concentration rate = SRT / HRT Equation 1
This concentration rate has an upper limit, and if it exceeds, it will flow into the treated water or clog the membrane. Therefore, in order to stably perform the membrane filtration operation, an operation in which SRT and HRT are adjusted so as not to exceed the limit of the concentration rate is performed. Here, SRT means the time required for the activated sludge in the reaction tank to be completely replaced by newly generated sludge. Specifically, it is determined based on the amount of extracted sludge (surplus sludge) and the reaction tank internal volume, and is expressed by the following relational expression (Formula 2).

SRT = reaction tank internal volume / amount of extracted sludge per unit time (2)
Moreover, HRT means time for inflow raw | natural water (to-be-processed water) to stay in a tank. Specifically, it is obtained based on the amount of inflow liquid and the reaction tank internal volume, and is expressed by the following relational expression (Formula 3).

HRT = reaction tank internal volume / inflow amount per unit time (formula 3)
As a result of the study by the inventors, the same tendency as other substances was observed for the oil component that continuously flows. That is, the highly biodegradable oil is biodegraded by activated sludge, and the hardly degradable oil is blocked by the membrane and accumulated and retained in the tank. The relationship between the oil retention concentration and the clogging of the membrane was verified by continuously supplying the oil using the membrane separation activated sludge experimental apparatus shown in Example 1. Specifically, during continuous operation, a part of the activated sludge in the tank is centrifuged (3000 rpm, 5 minutes) and separated into supernatant and other sludge (hereinafter referred to as “supernatant” and “sludge”, respectively). .) Each oil concentration was measured. As a result of measurement over time, it was found that when the upper limit of the oil concentration that can be retained in the supernatant in the tank was reached, the membrane was clogged. Furthermore, the sludge in the tank has a higher oil adsorption effect than the supernatant, and even if the oil concentration held in the supernatant reaches the upper limit, the sludge has an adsorption effect, so it will not clog the membrane immediately, It was found that the oil was retained in the tank.

  The behavior of the inflow oil in the activated sludge treatment tank is as follows. The oil component is retained in the supernatant due to the influence of specific gravity after flowing into the tank, but is then retained in the tank while adsorbing and aggregating to sludge by biodegradation, aeration, stirring, and the like. Even after reaching the upper limit of the supernatant retention concentration, the retention concentration in the tank increases due to the sludge adsorption effect, and when the sludge retention concentration reaches the upper limit, the excess moves to the supernatant and clogs the membrane ( Filtration pressure increases).

  Therefore, by controlling the oil concentration held in the supernatant or sludge without reaching the upper limit, it is possible to effectively suppress clogging of the membrane and perform stable operation maintenance.

  Thus, in order to control the oil concentration in the tank to a concentration that does not exceed the upper limit concentration of supernatant or sludge, it is achieved by appropriately setting the SRT and HRT related to the sludge extraction amount and sludge retention time. The More preferably, the oil concentration X flowing into the activated sludge treatment tank may be set based on the following relational expression (Formula 4).

Oil concentration X <retained oil concentration Y / concentration ratio (Formula 4)
(That is, X <(HRT / SRT) Y.)
Here, the retained oil concentration Y is increased not only by the supernatant concentration effect expressed by the concentration rate, but also by the effect of being adsorbed by the sludge. The sludge has the effect of adsorbing the oil α times the amount of the supernatant, and when the retention ratio is supernatant: sludge = 1: α, it can be expressed by the following relational expression (Formula 5).

Retained oil concentration Y = Supernatant oil concentration (1 + α) Formula 5
α varies depending on the properties of the oil. For example, the high viscosity oil component having a kinematic viscosity of 85 mm ² / s (at 40 ° C.) is 3 to 4, and the oil component having a kinematic viscosity of 32 mm ² / s (at 40 ° C.) is 1.5 to 2 It is.

  When calculating the retained oil concentration Y in the tank, the oil concentration can be adjusted before clogging the membrane by measuring the oil concentration separately from the supernatant and sludge. It is. The separation means for the supernatant and sludge is used for general solid-liquid separation of activated sludge, such as centrifugal separation and sedimentation separation, and any method capable of separating the supernatant and sludge may be used. Separation is more preferably used. Centrifugation conditions are not particularly limited, but are preferably performed under certain conditions in order to observe behavior changes during a series of evaluations, that is, during operation, for example, at 3000 rpm for 5 minutes. Is preferred.

  The following relational expression (Expression 6) is preferably used for calculating the oil concentration X expressed by (Expression 4) from (Expression 1) indicating the concentration ratio and (Expression 5) indicating the retained concentration in the tank. It is.

Oil concentration X <Supernatant oil concentration (1 + α) / (SRT / HRT) Equation 6
Based on such a relational expression, in order to satisfy the concentration of retained oil in the tank that allows stable membrane filtration operation, the amount and frequency of sludge extraction should be adjusted. Moreover, you may adjust the holding | maintenance ratio of the oil content in a tank by adding the chemical | medical agent with an oil content decomposition | disassembly effect or flocculant addition, reducing the amount of oil content of a supernatant, or improving a sludge adsorption effect. Furthermore, the tank activated sludge amount (MLSS) of the activated sludge treatment tank may be changed to increase the retained concentration Y in the tank. The amount of activated sludge in the tank (MLSS) referred to here represents the concentration of suspended solids in the activated sludge. The MLSS measurement method is not particularly limited as long as the suspended solids concentration can be quantified. For example, the evaporation residue measurement method and the suspended solid measurement method described in the sewage test method (Japan Sewerage Association) Are preferably used. Also, a commercially available MLSS densitometer may be used. The MLSS measurement method preferably used here is that activated sludge is solid-liquid separated by centrifugation or glass fiber filter paper, and then the residual solid is heated and dried at 105 to 110 ° C. for about 2 hours. Is calculated.

  Furthermore, it is also preferable to perform a pretreatment step upstream of the MF membrane filtration apparatus 2 and more preferably upstream of the activated sludge treatment tank and adjust the inflow concentration by means of oil removal means such as flotation separation. Here, examples of the pretreatment step that can be applied in the present invention include a pressure flotation separation device, an oil skimmer, a coagulation sedimentation device, and a stripping device. These are used for general oil separation and recovery, and are preferably used for oil components that have a small specific gravity and are likely to float, and oil components that flow in at a high concentration.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to these examples.

  Agricultural settlement wastewater treatment plant sludge is used as seed sludge, and three membrane-separated activated sludge treatment experimental equipment consisting of an activated sludge treatment tank and a filtered water tank for storing filtered water obtained by membrane filtration, respectively (A series) , B series, C series), and continuous filtration operation was performed in parallel. FIG. 1 shows an apparatus used in each of the A / B / C series. As water to be treated, tap water containing artificial sewage prepared with acetic acid, nitrogen and phosphorus and oil-containing water added with various oils were used. As the mineral oil, paraffin-based industrial raw material oil “Cosmo SP83” (manufactured by Cosmo Oil Lubricants Co., Ltd.) used in fiber oils and mold release agents was used. The oil content in the tank was measured by centrifuging the activated sludge in the tank (3000 rpm, 5 minutes), dividing it into sludge and supernatant, and measuring the n-hexane extract concentration over time. Table 1 shows the apparatus operating conditions.

(Comparative Example 1)
In the A series, as a result of continuous filtration using water to be treated containing 50 mg / L of oil, an increase in membrane filtration pressure was observed on the 19th day of operation. The oil concentration X at which stable operation was possible was 37 mg / L from the product of the retained oil concentration Y in the tank and the concentration rate.

Oil concentration X <(HRT / SRT) x supernatant retention concentration (1 + α) for stable operation
HRT = 3.5 days, SRT = 40 days,
Supernatant retention concentration 200mg / L, sludge retention concentration 220mg / L
Sludge adsorption effect α = 1.1
X [mg / L] <37
In this comparative example, X <(HRT / SRT) Y indicating the relational expression of the allowable oil concentration that can be stably operated was not satisfied, so it is considered that the membrane filtration pressure was increased.
Example 1
On the other hand, in the B series, the water to be treated was previously diluted with the water to be treated before containing the oil, and the continuous filtration operation was performed under the condition that the inflow oil concentration was adjusted to 25 mg / L (1/2 times). An operation in which the inflow oil concentration X was adjusted so that the allowable inflow concentration X, the concentration rate, and the oil retention amount Y in the tank satisfy the relational expression X <(HRT / SRT) Y was performed.

Oil concentration X <(HRT / SRT) x supernatant retention concentration (1 + α) for stable operation
HRT = 3.5 days, SRT = 40 days,
Supernatant retention concentration 200mg / L, sludge retention concentration 220mg / L
Reaction tank internal volume = 30L, amount of extracted sludge per unit time = 0.75L / day,
Inflow volume per unit time = 8.5L / day Sludge adsorption effect α = 1.1
X [mg / L] <37
As a result of continuous operation, stable operation was possible for about 30 days. In this example, the membrane filtration pressure did not increase because the operation satisfied the relational expression of the allowable oil concentration that allows stable operation.
(Example 2)
Furthermore, in C series, the water to be treated containing 50 mg / L of oil was used, the amount of sludge withdrawn in the tank was doubled, and the continuous filtration operation was performed under the condition of adjusting the concentration rate. The upper limit of X at this time is 73.5 mg / L, and the concentration rate is adjusted so that the inflow oil concentration X and the retained oil concentration Y in the tank satisfy the relational expression X <(HRT / SRT) Y of the allowable oil concentration Drove.

Oil concentration X <(HRT / SRT) x supernatant retention concentration (1 + α) for stable operation
HRT = 3.5 days, SRT = 20 days,
Supernatant retention concentration 200mg / L, sludge retention concentration 220mg / L
Reaction tank internal volume = 30 L, amount of extracted sludge per unit time = 1.5 L / day,
Inflow volume per unit time = 8.5L / day Sludge adsorption effect α = 1.1
X [mg / L] <73.5
As a result of continuous operation under these conditions, stable operation was possible for about 40 days. In this example, the membrane filtration pressure did not increase because the operation satisfied the relational expression of the allowable oil concentration that allows stable operation.

  From these results, the membrane separation activated sludge tank is controlled by controlling the inflow oil amount X, the concentration rate (SRT / HRT), and the retained oil concentration Y in the tank to satisfy the relationship of X <(HRT / SRT) Y. It was confirmed that stable operation was possible.

  The present invention is a treatment method that can be suitably used when oil-containing wastewater is subjected to membrane separation activated sludge treatment to obtain treated water.

1: treated water (raw water)
2: MF membrane filtration device 3: activated sludge treatment tank 4: filtered water tank 5: treated water 6: raw water supply pump 7: air supply device 8: aeration device 9: suction pump 10: sludge extraction pump 11: extraction sludge (surplus Sludge)

Claims (2)

Treatment of oil-containing wastewater having a membrane-separated activated sludge treatment process in which oil-containing wastewater is biologically treated in an activated sludge treatment tank and biologically treated by a membrane separation device installed in the activated sludge treatment tank. In the method, concentration of oil X flowing into the activated sludge treatment tank, concentration ratio represented by a ratio of solid residence time SRT and hydraulic residence time HRT (SRT / HRT ratio), retained oil content in the activated sludge treatment tank Treatment of oil-containing wastewater, wherein at least one of oil concentration X, solid residence time SRT, hydraulic residence time HRT, and retained oil concentration Y is controlled so that concentration Y satisfies the following relationship: Method.
X <(HRT / SRT) Y   It has a pretreatment step of pretreating oil-containing wastewater before the membrane separation activated sludge treatment step, and is contained in the oil concentration X flowing into the activated sludge treatment tank, and the supernatant and sludge in the activated sludge in the tank 2. The oil concentration according to claim 1, wherein at least one of a pretreatment process condition and a membrane separation activated sludge tank operation condition is controlled based on the measurement result. Treatment method for oil-containing wastewater.

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