JP5103747B2 - Water treatment apparatus and water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly maintain a permeation flux of a membrane without reducing a water recovering ratio in a water treating apparatus by a membrane separation after flocculating raw water. <P>SOLUTION: In treating water by flocculation through adding a flocculant to raw water and by membrane-separating the flocculated water, the concentration of organic materials in raw water is measured and the flocculation condition and the cleaning condition of the separating membrane are controlled from the measured value. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  In the present invention, wastewater treatment using natural water as a raw material or wastewater treatment for treating industrial wastewater or sewage, etc., by adding a flocculant to the raw water, suspended matter, colloidal components, organic substances, etc. in the raw water TECHNICAL FIELD The present invention relates to a water treatment apparatus and a water treatment method for performing membrane separation treatment with a separation membrane such as a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), and a nanofiltration membrane (NF membrane) after condensation and coarsening. In particular, the coagulant treatment conditions in the coagulation process are optimized to perform stable and efficient coagulation treatment, and the separation membrane cleaning conditions are optimized to reduce the water recovery rate without reducing the water recovery rate. The present invention relates to a water treatment apparatus and a water treatment method that maintain a high permeation flux of water.

  In water treatment using natural water as raw material and wastewater treatment for treating industrial wastewater or sewage, a flocculant is added to the raw water to condense and coarsen suspended substances, colloidal components, organic substances, etc. in the raw water Thereafter, a method of solid-liquid separation by precipitation, flotation, filtration, membrane filtration, or the like, or turbidity / sterilization by membrane filtration alone to recover treated water are performed.

  In this membrane separation device used for turbidity and sterilization, since the treatment continues, dirt adheres to the membrane surface and the membrane differential pressure increases, so the treated water (membrane permeated water) is periodically passed through the membrane. In order to maintain the membrane performance, the contaminants trapped on the membrane surface are discharged by a backwashing operation in which the secondary side is caused to flow backward from the secondary side to the primary side.

  However, natural water and wastewater often contain not only turbidity components mainly composed of inorganic clay minerals, but also organic substances such as humic substances and biological metabolites such as polysaccharides. When the membrane is contaminated, the membrane performance cannot be sufficiently recovered only by the back washing operation using the treated water.

  Regarding such organic contamination, the present applicant has previously proposed a method in which dilute cleaning chemicals are added to backwash water and backwashing is performed with a chemical solution (Japanese Patent Laid-Open No. 8-243361). However, even with this method, when the membrane permeation flux is set large, there is a problem that the membrane differential pressure increases rapidly when the organic matter concentration in the raw water increases. Although it is conceivable to increase the frequency of backwashing in order to suppress the increase in the membrane differential pressure, an increase in the frequency of backwashing leads to a decrease in the water recovery rate, which is not preferable.

  Further, in order to suppress membrane contamination due to organic substances, it is known to perform an agglomeration process prior to the membrane separation process and to perform the membrane separation process on the agglomerated water. For example, Japanese Patent No. 3312507 discloses such water. In the treatment, it is described that the addition amount of the flocculant is controlled based on the organic substance concentration of the treated water (membrane permeated water). However, even if such treatment is performed, membrane contamination due to organic substances cannot be sufficiently prevented, and there is a problem that when the concentration of organic matter in the raw water increases, the membrane differential pressure rapidly increases.

  By the way, the agglomeration treatment is for enhancing the membrane separation efficiency in the subsequent stage, and as the aggregating agent, generally an inorganic aggregating agent such as an aluminum salt or an iron salt is used. In many cases, a polymer flocculant is used in combination as an agglomeration aid for further coarsening the particles coagulated with the inorganic flocculant.

  In order to improve the agglomeration efficiency in the agglomeration treatment, it is important to smoothly diffuse and move the added aggregating agent and aggregating auxiliary agent into the raw water to increase the frequency of contact and collision with the agglomeration object. For this reason, a coagulation tank (hereinafter sometimes referred to as “stirring tank”) provided with a stirring means is generally used, and the raw water added with the coagulant is coagulated with stirring. The agitation tank generally includes a rapid agitation tank for agitation for contacting and colliding the agglomeration object and the aggregating agent in the raw water, and a slow agitation agitation tank for agitation for coarsening aggregated or agglomerated particles. It is divided into. As the stirring means, those using a stirring blade and those having a structure for stirring the raw water by bypassing the water channel are generally used. Moreover, the method of stirring during piping transfer using a pump and a static mixer is also used, and there is also an example using this together with a stirring tank.

  Aggregation or coagulation by inorganic flocculants is inhibited by humic substances present in the raw water, natural organic substances such as intracellular and extracellular metabolites produced by algae, and synthetic chemicals such as surfactants. The speed becomes slow or the agglomeration is poor.

  Conventionally, optimization of pH has been performed as a method for preventing this aggregation inhibition, and automatic pH adjustment is performed by linking a pH meter and an addition pump of an acid or alkaline pH adjuster. Yes. However, stable aggregation treatment cannot be performed only by pH adjustment.

  In the past, the mechanism by which natural organic substances such as humic substances contained in natural water and wastewater and synthetic chemicals such as surfactants cause aggregation inhibition has not been fully elucidated, and identification of these inhibitors It has not been done. For this reason, in the treatment of irrigation water and wastewater, in order to set the optimum flocculation conditions, an operation of determining the addition concentration and pH of the flocculating agent using a separate jar tester is essential, but such operation is generally complicated. It takes a long time to operate, and therefore, it cannot cope with fluctuations in the quality of raw water, and the determined amount of flocculant added and pH adjustment value cannot be immediately reflected, resulting in poor aggregation. .

  For this reason, at present, a method for preventing poor aggregation by setting the amount of the flocculant to be higher than the upper limit of the expected required amount in advance and adding the flocculant excessively is adopted. Yes. However, excessive addition of the flocculant in this way increases the chemical cost and increases the amount of sludge generated.

In addition, when an aluminum salt is used as a flocculant, if the amount of residual aluminum increases due to excessive addition, unaggregated aluminum causes a membrane contamination in membrane separation after the agglomeration treatment. In addition, due to the increase in residual aluminum, a large amount of unaggregated aluminum flows out in the filtered separation treated water. The residual aluminum concentration in the treated water is desired to be 100 μg / L or less.
JP-A-8-243361 Japanese Patent No. 3312507

  It is an object of the present invention to provide a water treatment apparatus and a water treatment method that maintain a high membrane permeation flux without reducing the water recovery rate in water treatment in which membrane separation treatment is performed after flocculation treatment in raw water. And

The water treatment apparatus of the present invention (Claim 1) is a flocculation treatment means for adding a flocculating agent to raw water and performing a flocculation treatment, and supplying the flocculation treatment water from the flocculation treatment means from the primary side and permeating the separation membrane. Membrane separation means for discharging permeated water from the secondary side, separation membrane washing means for washing the separation membrane by supplying a washing fluid, and an organic substance concentration in the raw water within a wavelength range of 230 to 300 nm. Organic substance concentration measuring means for measuring from the difference between the absorbance of light and the absorbance of visible light in the wavelength range of 600 to 700 nm, the absorbance of ultraviolet light in the range of 230 to 300 nm and the wavelength in the range of 600 to 700 nm based on the difference between the absorbance of visible light, and a control means for controlling the washing conditions in aggregation treatment conditions and the separation membrane cleaning means in the flocculation treatment unit directly, absorbance at a wavelength 260nm and the wavelength 660n Of raw water difference is more than 0.3abs between the absorbance, a water treatment apparatus for treating a membrane permeation flux 5.0 m / d or more, in coagulant addition amount of the aggregating process conditions wherein the controlling the raw water The cleaning condition to be controlled is a cleaning interval, the cleaning unit supplies the cleaning chemical as the cleaning fluid from the secondary side of the membrane separation unit, and discharges the cleaning chemical that has permeated through the separation membrane from the primary side When the separation membrane is back-washed with a chemical solution, the difference between the absorbance of ultraviolet light within a wavelength range of 230 to 300 nm and the absorbance of visible light within a wavelength range of 600 to 700 nm becomes a predetermined value or more. And threshold setting control for performing chemical backwashing.

The water treatment method of the present invention (Claim 2 ) comprises a flocculation process step of adding a flocculating agent to raw water and performing a flocculation process, and supplying flocculated water from the flocculation process step from the primary side of the membrane separation means for separation. A water treatment method comprising: a membrane separation step of discharging permeated water that has passed through a membrane from a secondary side of the membrane separation means; and a separation membrane cleaning step of cleaning the separation membrane by supplying a cleaning fluid. Is measured from the difference between the absorbance of ultraviolet light within a wavelength range of 230 to 300 nm and the absorbance of visible light within a wavelength range of 600 to 700 nm, and the absorbance of ultraviolet light within the wavelength range of 230 to 300 nm. The absorbance at 260 nm and the wavelength for directly controlling the agglomeration treatment conditions in the agglomeration treatment step and the washing conditions in the separation membrane washing step based on the difference between the absorbance of visible light in the wavelength range of 600 to 700 nm. A water treatment method for treating raw water having a difference from the absorbance at 660 nm of 0.3 abs or more with a membrane permeation flux of 5.0 m / d or more , wherein the controlled coagulation treatment condition is the amount of flocculant added to the raw water The cleaning condition to be controlled is a cleaning interval, and the cleaning step supplies a cleaning chemical as the cleaning fluid from the secondary side of the membrane separation means, and the cleaning chemical that has permeated the separation membrane from the primary side. The separation membrane is discharged and the chemical solution is back-washed. The difference between the absorbance of ultraviolet light in the wavelength range of 230 to 300 nm and the absorbance of visible light in the wavelength range of 600 to 700 nm is equal to or greater than a predetermined value. Threshold setting control for performing chemical backwashing at a time is performed.

According to the present invention, the permeation flux of the membrane can be maintained high without reducing the water recovery rate by controlling the aggregation treatment conditions and the separation membrane cleaning conditions based on the organic matter concentration of the raw water. .

  That is, by controlling the coagulation treatment conditions based on the concentration of organic matter in the raw water, it is possible to prevent excessive or insufficient coagulant addition amount, and therefore increase the chemical cost and increase sludge generation due to excessive coagulant addition. In addition to preventing deterioration of treated water quality due to insufficient aggregation, it is possible to perform good aggregation treatment, thereby obtaining good agglomerated water with low membrane contamination suitable as feed water for membrane separation. . In addition, since this good-quality agglomerated treated water is membrane-separated, membrane contamination can be reduced, and the washing conditions of the separation membrane can also be controlled based on the organic matter concentration of the raw water, thereby cleaning frequency. In addition, it is possible to employ appropriate cleaning conditions corresponding to the quality of raw water for the concentration of cleaning chemicals and the like, and as a result, the permeation flux of the membrane can be stabilized at a high value while maintaining a high water recovery rate.

In the present invention, the aggregation treatment conditions to control is a coagulant addition amount of the raw water.

Contact name organics concentration of the raw water, Ru can be easily measured from the difference between the absorbance of visible light in the range of absorbance and wavelength 400~800nm ultraviolet light in the wavelength range of 200 to 400 nm. That is, the absorbance of ultraviolet light within a wavelength range of 200 to 400 nm is the sum of the absorbance of organic matter and the absorbance of turbidity components mainly composed of inorganic clay minerals. Further, the absorbance of visible light within the wavelength range of 400 to 800 nm is the absorbance of turbidity components mainly composed of inorganic clay minerals. Therefore, the organic matter concentration in the raw water can be determined from the difference between both absorbances. The organic matter concentration in the raw water can be measured with a TOC meter or a COD meter. However, as described above, the organic matter concentration can be obtained easily and quickly if the difference in absorbance between ultraviolet light and visible light is suitable. is there.

  Hereinafter, embodiments of the water treatment apparatus and the water treatment method of the present invention will be described in detail.

  The raw water to be treated by the present invention contains organic matter, and examples include natural water such as river water and groundwater, as well as various factory wastewater, agricultural wastewater, and sewage. The organic matter contained in the raw water is not particularly limited. Natural water often contains humic acid, but naturally this humic acid is also a kind of organic matter of the present invention.

  In the present invention, after the raw water is coagulated, membrane separation is performed to obtain treated water, the organic matter concentration in the raw water is measured, and the coagulation treatment conditions and the separation membrane cleaning conditions are controlled based on the measured values.

The concentration of organic substances in the raw water, when determined from the difference between the absorbance and visible light absorbance of ultraviolet light of the raw water, ultraviolet light absorbance, wavelength 2 30 to 300 nm, for example, is the 260nm absorbance, visible light absorbance, waves The absorbance is set to a length of 600 to 700 nm, for example, 660 nm. The absorbance may be measured continuously or intermittently once every 1 to 10 minutes. Further, an average value of absorbance measurement values for 30 seconds to 1 day may be obtained, and this value may be used as an index value for control.

  As the flocculant added to the raw water in the raw water flocculation treatment, an aluminum flocculant such as polyaluminum chloride (PAC) or an iron salt such as ferric chloride can be used. You may use independently and may use 2 or more types together.

  In general, the aggregation treatment is performed at a pH of about 7.5 to 8.0. However, when an aluminum salt is particularly used as the aggregating agent, the pH is 5.0 to 7.0, particularly 5.5 to 6.5. When the value is lowered, the KMF value (time required for filtering a certain amount of sample water using a 0.45 μm membrane filter) can be improved. This is thought to be due to the fact that by lowering the pH to 5.0 to 7.0, particularly 5.5 to 6.5, the charge of aluminum increases and the coagulation action increases. However, when the pH is lowered to less than 5.0, the residual aluminum concentration increases. Therefore, an increase in the residual aluminum concentration is suppressed by adjusting the pH to 5.0 or more, preferably 5.5 or more. As a cause of increasing the residual aluminum concentration, if the pH is lowered too much, Al will have a high charge, but it will be a minimal size like ions that do not have much hydroxide, so even if neutralization is completed, This is probably because the cross-linking does not proceed and the film can only grow to a size that passes through the membrane.

In such agglomeration treatment, as a control item of the agglomeration treatment conditions to be controlled based on the measured value of the organic matter concentration of raw water,
(1) Amount of flocculant added
(2) (In the case of an aggregating apparatus equipped with a stirrer) There is a stirring speed of the stirrer, and only one of (1) and (2) may be controlled, or both may be controlled. Preferably, it is desirable to control the addition amount of the flocculant.

  Moreover, not only the organic matter concentration in the raw water, but also the agglomeration state of the agglomerated water is detected. The agglomeration treatment conditions may be controlled, whereby extremely good agglomeration treatment can be performed. In this case, as the aggregation state detection sensor, a light blocking fine particle sensor or a light scattering fine particle sensor that detects the clarity between the aggregate particles of the liquid in the aggregation tank can be used.

  In the present invention, the agglomerated water is then subjected to membrane separation. The agglomerated water is a solid substance contained in a sedimentation tank, a pressure levitation tank, a sand or other filtration device using a filler, and the like. After removal, the membrane may be subjected to membrane separation.

  Examples of the separation membrane for separating the flocculated water from the membrane include an MF membrane, a UF membrane, and an NF membrane. The membrane separation device may be of a cross flow type or a whole amount filtration type.

As a separation membrane cleaning method for membrane separation of flocculated water,
(1) Ordinary backwashing (washing water without chemicals (treated water (depermeable water), city water, industrial water, etc.) is supplied from the secondary side of the membrane, permeated through the separation membrane, and discharged from the primary side. What)
(2) Backwashing with chemicals (supplying chemicals from the secondary side of the membrane, permeating through the separation membrane and discharging from the primary side)
(3) Ordinary chemical cleaning (circulating cleaning chemicals to the primary side of the membrane)
(4) Flushing cleaning (gas flushing to the primary side and / or secondary side of the membrane)
And two or more of these may be used in combination.

  Among these, in particular, in the case of backwashing with the chemical solution of (2), a method of alternately adding acid and alkali in the vicinity of the specified concentration to the backwashing water is preferably used. In this case, after backwashing with one of the acid and alkali cleaning chemicals, it is allowed to stand for a certain period of time, and then backwashed with water to which no cleaning chemicals are added (treated water, city water, industrial water, etc.), then acid And after washing back with the other cleaning chemical solution of alkali, it may be allowed to stand for a certain period of time, and finally backwashed with water to which no chemical solution is added (treated water, city water, industrial water, etc.). Moreover, as shown in the below-mentioned Example, normal backwashing and chemical | medical solution backwashing can also be performed alternately.

  As the alkali of the cleaning chemical, sodium hypochlorite and sodium hydroxide are suitable, and examples of the acid include sulfuric acid, hydrochloric acid, nitric acid, citric acid, oxalic acid, ascorbic acid, sodium bisulfite and the like. It is not limited to these. An alkali and an acid may be used individually by 1 type, and may use 2 or more types together.

In addition, when using an acid and an alkali together, it is preferable that each density | concentration is the substantially same prescription | regulation (N). Usually, the acid and alkali concentrations are preferably about 1 × 10 ^{−3 to} 0.5N.

In such a separation membrane cleaning process, as a control item of the cleaning conditions to be controlled,
(1) Cleaning frequency (cleaning time, number of cleanings, cleaning interval, etc.)
(2) Cleaning fluid supply speed
(3) The chemical concentration of the cleaning chemical solution may be mentioned, and two or more of these may be controlled.

  Among the more specific cleaning condition control methods, the cleaning method of the cleaning frequency (cleaning interval) is as follows.

(1) In the case of normal backwashing Simple water backwashing without adding chemicals is usually performed at a rate of once every 30 seconds to 6 hours, preferably 5 minutes to 3 hours, particularly preferably 10 minutes to 3 hours. Is done. This washing interval is controlled by fluctuations in the concentration of organic matter in the raw water. Specifically, it is preferable to set about 1 to 10 threshold values of the organic substance concentration as a reference for control, and set the water backwashing cleaning interval for each.

(2) Backwashing with a chemical solution The chemical solution backwashing is preferably performed in combination with the above-described normal backwashing. In this case, normal backwashing is performed at the above-described cleaning intervals, and further, chemical backwashing is performed once every 0.5 to 10 days. The cleaning interval of this chemical backwashing is controlled by fluctuations in the organic matter concentration of the raw water. Specifically, one to three organic substance concentration thresholds serving as control criteria are set, and a cleaning interval is set for each.

  The chemical backwashing cleaning interval may be controlled based on the organic matter concentration of the raw water and the normal backwashing washing interval may be controlled. However, as shown in the examples described later, Is preferably a constant cleaning interval, and the cleaning interval of the chemical backwashing is preferably controlled based on the organic matter concentration of the raw water. This is because the chemical backwashing works more effectively against organic contamination.

  Alternatively, the organic matter concentration of the raw water may be integrated, and the chemical solution backwashing may be performed when the integrated value exceeds a predetermined value.

  In addition, when sodium hypochlorite is used as a chemical solution, it may be used in the same manner as the above-described “normal backwashing”. That is, when sodium hypochlorite is used as a chemical solution, the washing interval is 30 seconds to 6 hours, preferably 5 minutes to 3 hours, particularly preferably once every 10 minutes to 3 hours. Or may be used in combination with other chemical solutions or chemical solution backwashing using high-concentration sodium hypochlorite.

(3) Ordinary chemical cleaning Basically, chemical cleaning is performed when the membrane differential pressure exceeds a set value or when the converted membrane permeation flux (the membrane permeation flux when the temperature and pressure are set to predetermined values). However, in the present invention, chemical cleaning may be performed, for example, when the integrated value of the organic matter concentration of the raw water is equal to or higher than a predetermined value.

(4) Flushing cleaning With regard to the flushing cleaning, the cleaning interval may be controlled in the same manner as in the case of the normal backwashing described above.

  In (2) chemical backwashing and (3) chemical cleaning, the chemical concentration can be controlled according to the organic matter concentration in the raw water. In this case, the chemical concentration may be increased in proportion to the organic matter concentration of the raw water, and threshold control may be performed as in the case of controlling the cleaning interval.

  In the four types of cleaning described above, when supplying the cleaning fluid and cleaning the separation membrane, the supply speed of the cleaning fluid supplied based on the concentration of organic matter in the raw water may be controlled. This method is particularly useful in the case of a cleaning technique in which the cleaning fluid is supplied from the secondary side and the cleaning fluid that has passed through the separation membrane is discharged from the primary side.

  Also in this case, the supply speed of the cleaning fluid may be increased in proportion to the organic matter concentration of the raw water, or threshold control may be performed.

  In the present invention, the higher the organic matter concentration in the raw water, the higher the cleaning conditions, that is, for example, the higher the cleaning frequency, the longer the cleaning time, the higher the chemical concentration of the cleaning chemical solution, and the higher the supply rate of the cleaning fluid. In this case, the concentration of organic matter in the raw water and the washing conditions, for example, the concentration of the chemical solution and the frequency of washing may be linearly proportional to each other. The cleaning frequency may be increased stepwise. For example, the relationship between the concentration of organic matter in the water to be treated and the minimum necessary cleaning conditions that can sufficiently recover the filtration performance is obtained in advance by experiments, and this relationship is expressed in formulas or stored in the computer memory as it is. Based on this, the cleaning conditions may be determined.

  FIG. 2 schematically shows the results obtained by the present inventor's research on the relationship between the humic acid concentration in the raw water and the cleaning conditions (for example, the cleaning frequency) necessary to sufficiently recover the membrane differential pressure. It is a graph to show.

  The permeation flux Jc in FIG. 2 shows that when the organic matter concentration of the raw water is the same, when the membrane permeation flux is set to a higher value, the rate of increase of the membrane differential pressure ΔP increases rapidly, and the membrane separation operation is performed. Indicates the limit value that becomes impossible.

f ₁ , f ₂ , and f ₃ are, for example, the frequency of chemical cleaning, and f ₁ <f ₂ <f ₃ . When the membrane cleaning is controlled so that the permeation flux recovers to A [m / d] and the filtration operation is performed with this permeation flux, the frequency of chemical cleaning is f ₁ when the humic acid concentration is 0.8 a or less. and then, the frequency of 0.8a~0.8b the chemical cleaning and _{f 2,} and _{f 3} the frequency of chemical cleaning at 0.8B～0.8C. When the humic acid concentration C ₀ is a and the frequency of chemical cleaning is f ₁ when the humic acid concentration C ₀ is a, the reverse permeation flux becomes the limiting membrane permeation flux, and the pressure difference is rapidly increased. This is because there is a risk of the rise.

  Although not shown, it was recognized that there is a relationship shown in FIG. 2 between the organic substance concentration in the raw water and the cleaning conditions such as the chemical solution concentration, the supply speed of the cleaning fluid, and the cleaning time.

  Thus, by increasing the cleaning conditions such as the concentration of the cleaning chemical and the cleaning frequency as the concentration of organic matter in the raw water increases, the membrane performance of the separation membrane can be reliably and sufficiently recovered even when the concentration of organic matter is high. In addition, when the organic matter concentration in the raw water is low, the consumption of cleaning fluid such as cleaning chemicals is reduced to reduce the chemical concentration, reduce the frequency of chemical cleaning, or reduce the supply rate of cleaning fluid accordingly. Less, it is possible to save cleaning fluid such as cleaning chemicals, and to prevent film deterioration. When membrane permeated water is used as rinsing water or cleaning fluid after chemical cleaning, the water recovery rate can be increased by reducing the frequency of cleaning the chemical and the supply rate of the cleaning fluid.

  As shown in Examples 1 and 2 to be described later, when the frequency of chemical cleaning is increased in accordance with the increase in the concentration of organic substances in the raw water, a sufficient chemical cleaning effect can be obtained even if the concentration of the chemical is decreased. It was recognized that

Embodiments of a water treatment apparatus and a water treatment method of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a system diagram showing an embodiment of a water treatment apparatus of the present invention.
In FIG. 1, I is an agglomeration processing part, and II is a membrane separation part.

  Reference numeral 1 denotes a raw water tank, which includes an absorbance measuring device 21. Reference numeral 2 denotes a coagulation agitation tank, which includes an agitator 22, a pH sensor 23, and an aggregation state detection sensor 24. 11 is a flocculant storage tank, and the flocculant in the storage tank 11 is supplied to the flocculent stirring tank 2 through the piping 33 from the flocculant chemical injection pump 33P. Reference numerals 12 and 13 denote an acid storage tank and an alkali storage tank, respectively, and the acid in the storage tank 12 is supplied to the agglomeration stirring tank 2 via the pipes 34 and 36 by an acid chemical injection pump 34P. Moreover, the alkali in the storage tank 13 is supplied to the aggregation stirring tank 2 through the pipes 35 and 36 by the alkali chemical injection pump 35P. 6 is an agglomeration treatment condition control device, to which the detection value of the absorbance measuring device 21, the detection value of the pH sensor 23, and the detection value of the aggregation state detection sensor 24 are inputted, and the flocculant chemical injection pump 33P, the acid chemical injection pump 34P and A rotation speed control signal of the alkaline chemical injection pump 35P is output. Further, the detection value of the absorbance measuring device 21 input to the control device 6 is output to a chemical solution backwash condition control device 7 described later.

  In the agglomeration processing unit I, the raw water is introduced into the raw water tank 1 through the pipe 31, the organic substance concentration in the raw water is detected by the absorbance measuring device 21, and the detection result is input to the control device 6. As described above, the absorbance measuring device 21 is preferably equipped with an ultraviolet light absorbance meter having a wavelength of 200 to 400 nm and a visible light absorbance meter having a wavelength of 400 to 800 nm. The absorbance measuring device 21 may be an immersion type or a badge type.

  The raw water in the raw water tank 1 is introduced into the aggregation stirring tank 2 through the pipe 32. In the flocculation agitation tank 2, the raw water is agglomerated by adding the flocculant in the flocculant storage tank 11 by the chemical injection pump 33 </ b> P, adjusting the pH by addition of acid and alkali, and stirring by the stirrer 22. The pH in the agglomeration stirring tank 2 is detected by the pH sensor 23, and the detection result is input to the control device 6. The detection value of the aggregation state detection sensor 24 is also input to the control device 6.

  The amount of the flocculant added to the aggregation stirring tank 2 is controlled based on the detection value of the absorbance measuring device 21. That is, for example, in the control device 6, the input detection value of the absorbance measuring device 21 is substituted into a preset determination formula for the amount of flocculant added, and the rotation speed of the drug injection pump 33P is controlled based on the calculation result. An appropriate amount of flocculant is added. A commercially available variable metering pump or the like is used as the chemical injection pump 33P.

  In order to control the addition amount of the flocculant according to the organic substance concentration of the raw water, the organic substance concentration obtained by the absorbance measuring device 21 may be multiplied by a coefficient to calculate the flocculant addition amount. Since it is proportional to the difference between the light absorbance and the visible light absorbance, it is preferable to calculate the addition amount of the flocculant by multiplying the difference between the ultraviolet light absorbance and the visible light absorbance by the coefficient M as shown in the following equation.

Addition amount of flocculant = M × [(ultraviolet part absorbance) − (visible part absorbance)]
The coefficient M is a coefficient determined in advance from the KMF value measured by a jar test using raw water, and it is not always necessary to adjust M for each raw water.

In addition, it is good also as threshold value control instead of the flocculant addition amount control proportional to an absorbance difference in this way. The threshold control, the absorbance difference is a weight flocculant when less than a predetermined value a ₁ and b _1, the amount of flocculant added when the absorbance difference is a predetermined value a ₁ ~a ₂ and b _2, the absorbance difference is a predetermined value When it exceeds a _2, for example, the addition amount of the flocculant is b ₃ , but it is not limited thereto.

  The acid and alkali chemical injection pumps 34 </ b> P and 35 </ b> P are controlled by the control device 6 so that the pH in the aggregation stirring tank 2 is 5.0 to 7.0, preferably 5.0 to 6.5. In the case of reducing the residual aluminum concentration, it is preferable to control the pH to be 5.5 to 7.0, particularly 6.0 to 7.0, particularly 6.0 to 6.5 as described above.

  The aggregation state detection sensor 24 can be used to correct the addition amount of the aggregating agent or to send an alarm signal when an aggregation failure occurs. Further, the stirring speed of the stirrer 22 may be controlled based on the detection value of the aggregation state detection sensor 24. In order to control the amount of the flocculant added to the aggregation stirring tank 2 by the chemical injection pump 33P based on the detection value of the absorbance measuring device 21 and the detection value of the aggregation state detection sensor 24, for example, in the control device 6 Then, the detected value of the absorbance measuring device 21 is substituted into a predetermined formula for determining the addition amount of the flocculant, and based on the calculation result, the rotational speed of the drug injection pump 33P is controlled, and the detection value of the aggregation state detection sensor 24 is detected. Based on the above, the rotational speed of the medicine pump 33P is corrected.

  As this agglomeration state detection sensor 24, a device and a sensor for detecting the turbidity of the supernatant obtained by transferring the liquid in the agitation agitation tank 2 to another precipitation tank and settling for a certain time, or the zeta potential of the aggregated or agglomerated particles. Although a device and a sensor for detecting the flow potential can be used, a light-blocking fine particle sensor or a light scattering fine particle sensor for detecting the fineness between particles condensed or aggregated in the aggregation stirring tank 2 is preferable. Used for.

  The agglomerated water thus agglomerated by adding and aggregating the aggregating agent in the agitation agitation tank 2 is fed to the membrane separation unit II.

  In this membrane separation part II, 3 is a membrane water supply tank, 4 is a membrane module, 5 is a treated water tank, 7 is a chemical backwash condition control device, 14 is an alkali storage tank, and 15 is an acid storage tank. The pipe 38 that supplies the agglomerated treated water in the membrane water tank 3 to the membrane module 4 includes a water supply pump 38P and a bubble 38V. A bubble 39V is provided in the pipe 39 for supplying the membrane permeated water of the membrane module 4 to the treated water tank 5, and the alkali in the alkali storage tank 14 passes through the pipe 43 from the alkali chemical injection pump 43P. The acid in the acid storage tank 15 is supplied via the pipe 44 by the acid injection pump 44P, and the treatment water in the treatment water tank 5 is supplied via the pipe 42 by the backwash pump 42P. ing.

  41 is a discharge pipe for backwash drainage, and 40 is a discharge pipe for treated water (membrane permeated water). Each piping 39, 41, 42, 43, 44 is provided with valves 39V, 41V, 42V, 43V, 44V, respectively, and a control signal from the control device 7 is sent to each pump 38P, 42P, 43P, 44P, and each valve 38V. , 39V, 41V, 42V, 43V, 44V.

  The agglomerated treated water in the membrane water tank 3 is sent to the primary side 4a of the membrane module 4 through the water supply pump 38P and the valve 38V. In this embodiment, the membrane module 4 is a total filtration method, but may be a cross flow method. The membrane permeated water that has permeated the membrane and entered the secondary side 4b is introduced into the treated water tank 5 through the pipe 39 and is discharged out of the system through the pipe 40. A pipe 41 for taking out backwash drainage is connected to the primary side 4 a of the membrane module 4.

  In order to backwash the membrane module 4 with water or to rinse after the chemical liquid backwashing, the water in the treated water tank 5 can be supplied to the pipe 39 upstream of the valve 39V via the pipe 42. Further, in order to perform chemical cleaning of the membrane module 4, the acid solution in the acid storage tank 15 can be supplied to the pipe 39 upstream of the valve 39V via the pipe 44, and the alkali solution in the alkali storage tank 14 can be supplied. Can be supplied through the pipe 43.

  When the membrane module 4 is backwashed with water or rinsed after the chemical backwashing, the pump 38P is stopped, the valves 38V, 39V, 43V, 44V are closed, the valves 42V, 41V are opened, and the pump 42P is operated. As a result, the treated water in the treated water tank 5 is supplied to the secondary side 4b of the membrane module 4 through the pipes 42 and 39, and the membrane permeates in the reverse direction to the primary side 4a. Discharged.

  When the membrane module 4 is backwashed with alkali or acid, the pump 38P is stopped, the valves 38V and 39V are closed, the valve 43V or 44V is opened, the valve 41V is opened, and the pump 43P or 44P is operated. Then, the valve 42V is opened, the pump 42P is operated, a predetermined amount of water is sent from the treated water tank 5 to the pipe 39, and sent to the membrane module 4 while diluting alkali or acid.

  When the concentration of alkali or acid supplied to the membrane module 4 is changed, the injection amount of alkali or acid is changed by inverter or pulse control of the pump 43P or 44P.

  The detection value of the absorbance measuring device 21 in the raw water tank 1 is input to the control device 7 via the control device 6. The control device 7 controls the frequency of chemical backwashing and / or the concentration of chemical supplied to the membrane module 4 (injection amount of alkali or acid from the tank 14 or 15) according to the detection value of the absorbance measuring device 21.

  The supply rate of the backwash fluid during water backwashing or chemical solution backwashing may be controlled. In that case, the rotational speed of each pump 42P, 43P, 44P is controlled so as to be a predetermined feed rate. 7 to control.

  FIG. 1 shows an example of an embodiment of the present invention, and the present invention is not limited to the embodiment of FIG. 1 as long as the gist thereof is not exceeded.

  For example, the flocculation agitation tank may have a two-tank configuration including a rapid agitation tank and a slow agitation tank into which the effluent water from the rapid agitation tank is introduced. A flocculant may be added and an organic polymer flocculant may be added to the subsequent slow stirring tank. In addition, as described above, the agglomerated water may be subjected to membrane separation after removing solids contained in a sedimentation tank, a pressurized flotation tank, a filtration device using sand, or other fillers. In this case, a sedimentation tank and a filtration device are provided in the subsequent stage of the aggregation stirring tank 2 in FIG.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Example 1
In accordance with the present invention, using raw water tanks, rapid stirring tanks and slow stirring tanks, sedimentation tanks, sand filtration tanks, and UF membrane modules, raw water is converted into raw water tanks → rapid stirring tanks → slow stirring tanks → Water was passed in the order of precipitation tank → sand filtration tank → membrane module for treatment.

As the sand filtration tank, a column in which 600 mm of filtration sand having an effective diameter of 0.45 mm was stacked was used. The rapid stirring tank is a square rapid stirring tank with a paddle type stirrer (200 rpm, 40 W) having an effective capacity of 30 L, and the slow stirring tank is a paddle type stirring machine (15 r.p with an effective capacity of 100 L). M., 40 W), two slow agitation tanks connected in series. As the membrane module, a small laboratory module (membrane area: 0.14 m ² ) of an internal pressure hollow fiber ultrafiltration membrane (hydrophilic polysulfone, molecular weight cut off 150,000) manufactured by Kuraray Co., Ltd. was used.

  As raw water, humic acid dissolved in tap water was adjusted to 0.5, 3.2 and 4.5 mg / L, respectively, and each humic acid addition concentration was changed every week. Raw water is treated at 600 L / h, polyaluminum chloride (PAC) is added as a flocculant to the rapid stirring tank, and acid or alkali is added so that the pH of the rapid stirring tank is 6.5. Adjustments were made.

  In the raw water tank, an S :: CAN sensor (S :: CAN MESSTECHNIK GMBH (Austria), cell width 50 mm), which can scan the ultraviolet to visible light region with a wavelength of 200 nm to 700 nm, is immersed in the raw water tank. Was measured at a wavelength of 260 nm, and the absorbance of visible light was measured at a wavelength of 660 nm.

The amount of PAC added to the rapid stirring tank is controlled based on the difference between the absorbance E ₂₆₀ of ultraviolet light and the absorbance E _{660 of} visible light (E ₂₆₀ −E ₆₆₀ ) measured by an absorbance meter. mg / L) = 100 × (E ₂₆₀ −E ₆₆₀ ) (abs). The absorbance difference (E ₂₆₀ -E ₆₆₀ ) was similarly examined for sand filtrate.

The membrane permeation flux in the membrane module is constant at 4.5 m / d for the first 3.5 days of water flow at each humic acid concentration and at 5.5 m / d for the second half of the day. In addition to performing normal water backwashing every 29 minutes for 1 minute and performing chemical backwashing regularly every week, the difference in absorbance (E ₂₆₀ -E ₆₆₀ ) is 0.3 abs or more. As the threshold setting control performed at that time, it was set to be performed once a day (medical solution backwash interval 24 hours).

  The chemical liquid back washing process was as shown in Table 1 below. In addition, sodium hydroxide was used as the alkali and sulfuric acid was used as the acid.

  The rate of increase of the membrane differential pressure of the separation membrane under each raw water and membrane permeation flux conditions was examined, and the results are shown in Table 4 together with the amount of PAC added, the difference in absorbance of sand filtration water, and the presence or absence of chemical backwashing. In addition, the membrane differential pressure increasing speed in the table is an average value.

Example 2
In Example 1, the chemical solution backwashing step performed when the absorbance difference (E ₂₆₀ -E ₆₆₀ ) becomes 0.3 abs or more is as shown in Table 2 below, and the chemical solution concentration is halved as compared with Example 1. On the other hand, water treatment was performed in the same manner except that the chemical liquid backwash frequency was doubled and chemical liquid backwashing was performed at 12-hour intervals, and the results are shown in Table 4.

Example 3
In Example 1, the chemical solution backwashing step performed when the absorbance difference (E ₂₆₀ -E ₆₆₀ ) becomes 0.3 abs or more is as shown in Table 3 below, and the chemical solution concentration is halved as compared with Example 1. On the other hand, the water treatment was performed in the same manner except that the supply rate of the cleaning liquid was doubled to 10 m / d, and the results are shown in Table 4.

Comparative Example 1
In Example 1, water treatment was performed in the same manner except that the chemical solution backwashing was not performed in the threshold setting control, and the results are shown in Table 4.

Table 4 shows the following.
In Examples 1 to 3, when the humic acid addition concentration is set to 4.5 mg / L, the chemical solution by the threshold setting control when the organic matter concentration of raw water (E ₂₆₀ -E ₆₆₀ ) exceeds 0.3 abs. Since backwashing was performed, no increase in the rate of increase in the membrane differential pressure was observed even when the membrane permeation flux was set as high as 5.5 m / d.

Even in Comparative Example 1 in which the chemical solution was not backwashed, even when 4.5 mg / L of humic acid was added and the organic matter concentration (E ₂₆₀ -E ₆₆₀ ) of the sand filtration water was 0.044 abs, the membrane permeation flow When the bundle was set to 4.5 m / d, the increase rate of the membrane differential pressure was stable at 1.0 kPa or less. However, when the membrane permeation flux is set to 5.5 m / d and humic acid is added to the raw water at 4.5 mg / L, the increase rate of the membrane differential pressure is 2 kPa / d or more, and the stable operation is continued. It became impossible. However, when the humic acid addition concentration of the raw water was lowered to 0.5 mg / L and 3.2 mg / L, the membrane differential pressure recovered spontaneously, and no increase in the rate of increase in the membrane differential pressure was observed.

  From these results, the organic matter concentration of the raw water is measured, and the coagulation conditions (addition amount of coagulant) are controlled based on the results. At the same time, the separation membrane washing conditions (frequency of chemical backwashing, chemical concentration of chemicals and washing) It can be seen that the operation can be stably continued with a high membrane permeation flux by controlling the fluid supply speed.

Such an effect of the present invention is particularly effective when the concentration of organic matter in raw water (E ₂₆₀ -E ₆₆₀ ) is 0.3 abs or more and the permeation flux of the membrane is set as high as 5.0 m / d or more. I understand that there is.

It is a systematic diagram which shows embodiment of the water treatment apparatus of this invention. It is a graph which shows typically the relation between humic acid concentration and washing conditions (backwash frequency).

I Aggregation processing section
II Membrane Separation Unit 1 Raw Water Tank 2 Coagulation Stirring Tank 3 Membrane Water Supply Tank 4 Membrane Module 5 Treatment Water Tank 6 Coagulation Treatment Condition Control Device 7 Chemical Liquid Backwash Condition Control Device 11 Coagulant Storage Tank 12, 15 Acid Storage Tank 13, 14 Alkali Storage Tank 21 Absorbance Measuring device 22 Stirrer 23 pH sensor 24 Aggregation state detection sensor

Claims (2)

A coagulation treatment means for adding a coagulant to the raw water and coagulating it;
A membrane separation means for supplying agglomerated treated water from the agglomeration treatment means from the primary side and discharging permeated water that has permeated the separation membrane from the secondary side;
A separation membrane cleaning means for cleaning the separation membrane by supplying a cleaning fluid;
Organic matter concentration measuring means for measuring the organic matter concentration in the raw water from the difference between the absorbance of ultraviolet light within a wavelength range of 230 to 300 nm and the absorbance of visible light within a wavelength range of 600 to 700 nm;
Based on the difference between the absorbance of ultraviolet light within the wavelength range of 230 to 300 nm and the absorbance of visible light within the wavelength range of 600 to 700 nm, the aggregation treatment condition in the aggregation treatment means and the washing condition in the separation membrane washing means A water treatment apparatus for treating raw water having a difference between the absorbance at a wavelength of 260 nm and the absorbance at a wavelength of 660 nm of 0.3 abs or more at a permeation flux of 5.0 m / d or more. And
The coagulation treatment condition to be controlled is the amount of coagulant added to the raw water,
The cleaning condition to be controlled is a cleaning interval,
The cleaning means supplies a cleaning chemical solution as the cleaning fluid from the secondary side of the membrane separation means, discharges the cleaning chemical solution that has permeated the separation membrane from the primary side, and backwashes the separation membrane with the chemical solution. ,
Threshold setting control for performing chemical liquid backwashing is performed when the difference between the absorbance of ultraviolet light within a wavelength range of 230 to 300 nm and the absorbance of visible light within a wavelength range of 600 to 700 nm exceeds a predetermined value. Water treatment equipment. A coagulation treatment step of adding coagulant to the raw water and coagulating,
A membrane separation step of supplying the agglomerated water from the agglomeration treatment step from the primary side of the membrane separation means, and discharging the permeated water that has permeated the separation membrane from the secondary side of the membrane separation means;
In a water treatment method having a separation membrane cleaning step of cleaning the separation membrane by supplying a cleaning fluid,
The organic substance concentration in the raw water is measured from the difference between the absorbance of ultraviolet light within a wavelength range of 230 to 300 nm and the absorbance of visible light within a wavelength range of 600 to 700 nm, and the ultraviolet concentration within the wavelength range of 230 to 300 nm is measured. An absorbance and a wavelength of 260 nm that directly control the aggregation treatment conditions in the aggregation treatment step and the washing conditions in the separation membrane washing step based on the difference between the light absorbance and the absorbance of visible light in the wavelength range of 600 to 700 nm. A water treatment method for treating raw water having a difference from the absorbance at 660 nm of 0.3 abs or more with a membrane permeation flux of 5.0 m / d or more ,
The coagulation treatment condition to be controlled is the amount of coagulant added to the raw water,
The cleaning condition to be controlled is a cleaning interval,
In the cleaning step, a cleaning chemical solution as the cleaning fluid is supplied from the secondary side of the membrane separation means, and the cleaning chemical solution that has permeated the separation membrane is discharged from the primary side to back-clean the separation membrane. ,
Threshold setting control for performing chemical liquid backwashing is performed when the difference between the absorbance of ultraviolet light within a wavelength range of 230 to 300 nm and the absorbance of visible light within a wavelength range of 600 to 700 nm exceeds a predetermined value. Water treatment method.

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