JP2008173534A - Water treatment method and water treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment method for enhancing a recovery without deteriorating a treatment capacity, and a water treatment apparatus. <P>SOLUTION: The water treatment method includes a separation process A for performing flocculation pressure flotation separation and/or flocculation/sedimentation separation after raw water is once stored in a raw water storage tank, a separation process B for subjecting the treated water obtained in the separation process A to filtering treatment and a separation process C for separating the treated water obtained in the separation process B using a reverse osmosis membrane to obtain permeating water. The separation process B has a washing process and the washing waste water produced in the washing process is refluxed to the raw water storage tank. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a water treatment method and apparatus suitably used for recycling wastewater such as sewage and factory wastewater and desalination of seawater or brine.

  When reclaiming sewage or factory wastewater, depending on the nature of the wastewater, after the primary treatment by the activated sludge method, etc., secondary treatment such as coagulation sedimentation separation and coagulation pressure flotation separation is performed, and further filtration After the tertiary treatment by the vessel, it is necessary to improve the treated water to a reusable water quality using a reverse osmosis membrane or an ion exchange resin.

  In addition, when desalinating seawater and brine, depending on the properties of the raw water, the raw water is subjected to coagulation sedimentation separation and coagulation pressure floatation separation treatment, followed by filtration treatment as in the case of wastewater reclamation treatment. May be used for desalination.

  In such a water treatment process, it is desirable to keep the necessary cost as low as possible. However, as one of the methods, the recovery rate in the reverse osmosis membrane or the ion exchange treatment is increased, and the pretreatment (1st to 3rd order) is performed. In general, a method of reducing the processing cost and reducing the processing cost is used.

  Typically, typical processes used for wastewater reclamation and seawater desalination include agglomerated sand filtration + reverse osmosis membrane treatment, agglomeration sediment + sand filtration + reverse osmosis membrane treatment, and agglomeration pressure flotation separation. + Sand filtration + Reverse osmosis membrane treatment, but in each unit process, there is an upper limit to the recovery rate, which is the ratio of treated water to feed water, and it depends on the quality of the feed water. The sand filtration is 95%, the reverse osmosis membrane treatment is 90% for wastewater reclamation treatment, and about 60% for seawater desalination.

  Above all, the reason why the upper limit recovery rate of filtration process such as agglomerated sand filtration does not reach 100% is that, for example, sand filtration and polishing filtration regularly backwash the dirt accumulated in the filtered sand (usually once a day). This is because the filtered water is used.

  Therefore, even if an attempt is made to increase the recovery rate of the filter in order to reduce the processing cost, it is difficult to operate above the upper limit with the current operation method, and the backwash water amount is forcibly reduced or the backwash interval is reduced. If the recovery rate is increased by a method such as extending the pressure, the filtered water quality decreases or the filtration differential pressure increases, and stable operation becomes difficult.

  Moreover, as a means for improving the recovery rate of the filter, Patent Document 1 discloses a method of performing backwashing using raw water instead of filtered water. In this case, since the treated water is certainly not wasted, a high recovery rate of almost 100% can be obtained. However, this is limited to the case of relatively clear raw water, and it can be applied to sewage and factory wastewater after backwashing. It is difficult because the quality of treated water deteriorates.

  Also, regarding the recovery rate in reverse osmosis membrane treatment, forcibly increasing the quality of the treated water deteriorates, scale components precipitate in the concentrated water and membrane performance and membrane life are reduced, or the operating pressure increases. There are problems such as high processing costs (power costs), and it is difficult to easily increase the recovery rate.

  In order to avoid the above problems, Patent Document 2 discloses that a filter or a biological treatment device is disposed after pressurized flotation separation in sewage treatment, and once these backwash wastewater is stored, a predetermined amount is obtained by a pump. Is returned to the pressure levitation device to increase the recovery rate. However, this method can cope with high turbidity raw water with a suspended solid concentration of about 200 mg / l, but the suspended solid concentration in the backwash waste water to be returned is very high, thousands to tens of thousands mg / l. Therefore, in order to stabilize the processing performance in the separation process, the wastewater from the filtration process is temporarily stored, and a predetermined amount is returned little by little with a dedicated pump so that the quality of the water supplied to the separation process does not fluctuate extremely. It was necessary to inject a new flocculant into the backwash wastewater to be returned, and incidental facilities were indispensable.

As described above, in the water treatment process using the combination of the current filter and the reverse osmosis membrane, there is a limit in improving the recovery rate without deteriorating the treatment performance by a simple method.
JP 58-45708 A JP-A-6-170395

  In order to solve the above-mentioned problems, the present invention has intensively studied on methods for improving the recovery rate in wastewater reclamation treatment and seawater or brine desalination, and as a result, the following invention has been achieved. That is, the present invention includes a separation step A in which raw water is once stored in a raw water storage tank and then subjected to coagulation pressure flotation separation and / or coagulation sediment separation, and a separation step B in which treated water obtained in the separation step A is filtered. And a separation step C for separating the treated water obtained in the separation step B by reverse osmosis membrane to obtain permeated water, wherein the separation step B has a washing step and is generated in the washing step The water treatment method of recirculating the washing waste water to be returned to the raw water storage tank. Further, the present invention provides a separation means A comprising a raw water storage tank and a coagulation pressure flotation separation device and / or a coagulation sedimentation separation apparatus provided at a subsequent stage of the raw water storage tank, and a subsequent stage of the separation means A. A separation means B provided with a filter; and a separation means C provided with a reverse osmosis membrane separation device provided downstream of the separation means B, wherein the separation means B is used to wash the filter. The water treatment device is provided with means for returning the washing waste water generated by the above to the raw water storage tank.

  As described above, in the present invention, after the raw water is temporarily stored, the aggregated precipitation separation and / or the aggregated pressurized flotation separation (separation step A) and the filtration step (separation step B) are performed in combination as the pretreatment step. Then, reverse osmosis membrane separation (separation step C) is performed.

  The coagulation sedimentation separation uses an apparatus comprising a reaction tank for adding a coagulant to the raw water to cause an aggregation reaction, an aggregation tank for growing the aggregate formed in the reaction tank, and a precipitation tank for precipitating and separating the grown aggregate. The turbidity contained in the raw water is periodically discharged from the settling tank as agglomerated sludge.

  On the other hand, agglomeration pressure flotation separation is performed by adding a flocculant to raw water and agglomerating reaction, agglomeration tank for growing agglomerates formed in the reaction tank, and a flotation separation tank for separating the agglomerates by attaching them to bubbles. The turbidity contained in the raw water is periodically discharged from the floating separation tank as floating scum.

  The flocculant used in the flocculent precipitation separation treatment or the flocculent pressure flotation separation treatment is not particularly limited as long as it has an effect of capturing and flocculating turbidity in the raw water. For example, polyaluminum chloride ( PAC), aluminum sulfate, ferric chloride, ferric sulfate, polysilica iron (PSI), and other inorganic or inorganic polymer flocculants, and organic polymer flocculants such as polyacrylamide can be used. However, assuming that the unreacted flocculant leaks to the reverse osmosis membrane in the latter stage, it is preferable to use ferric chloride that is difficult to adsorb on the reverse osmosis membrane. Further, the structure of the reaction tank and the coagulation tank and the kind of the stirrer are not particularly limited, and are appropriately selected and designed according to the properties of the raw water.

  For the filter used in the separation step B combined with the above coagulation sedimentation or coagulation pressure floatation separation, the suspended components remaining in the water treated by the coagulation sedimentation separation or coagulation pressure floatation separation are removed and processed. The purpose is to further clarify the water and make it suitable for the feed water for the subsequent reverse osmosis membrane treatment, and a sand filter is usually used.

  As the sand filtration, single layer filtration using garnet or silica sand, two layer filtration combining anthracite and the garnet or silica sand, or three layer filtration can be used, which is appropriately selected depending on the quality of raw water. Further, the sand filtration may be a single stage, but may be a multi-stage filtration appropriately combining the above methods, for example, a two-layer filter composed of anthracite and silica sand at the front stage of the filter, and a rear stage. It is good also as two-stage filtration which combined the single layer filter which consists of quartz sand. The particle size of the filter sand used in the sand filter is not particularly limited and can be appropriately selected according to the quality of the raw water, but the increase in the filtration differential pressure due to clogging of the sand layer is small, and the water quality obtained is In order to improve the stability and enable stable operation, it is preferable to use the one in the range of 0.8 to 1.5 mm in the case of anthracite and in the range of 0.4 to 0.7 mm in the case of silica sand or garnet.

  During the operation of the sand filter, the treated water of the preceding flocculation / separation separation or flocculation / pressure flotation separation may be allowed to flow as it is and filtered, but the flocculant or disinfectant is added to the supply water upstream of the sand filter. If the chemicals are injected and filtered, fine turbidity, organic matter, or microorganisms in the raw water that could not be removed by coagulation sedimentation separation or cohesive pressure flotation separation will aggregate and can be easily removed by sand filtration. Become. The type of the flocculant used here is not particularly limited, and the same flocculant as that used in the previous stage of flocculation precipitation separation and flocculation pressure floating separation can be used. Furthermore, regarding the sand filtration system, there are a pressure filtration system for filtering by applying pressure to the feed water and a gravity filtration for filtering by a head difference without applying pressure, but in the present invention, any system is used. Also good.

  In the filtration process such as sand filtration described above, turbidity is trapped in the sand layer during operation. Therefore, if the operation is continued, the filtration performance decreases. Therefore, in order to maintain the filtration performance, it is necessary to periodically perform backwashing, rinsing or the like to clean the sand layer or the membrane surface and discharge it outside the system. The period of these washing steps is appropriately determined depending on the degree of contamination of the raw water and the situation of the increase in the filtration differential pressure. Usually, in the case of sand filtration, about once every two days, the backwash time is 30. Performed at a rate of ~ 60 minutes.

  Here, the backwashing or rinsing washing wastewater usually contains high-concentration turbidity and is not recycled and discarded as wastewater. That is, if the concentration of suspended solids in raw water is at a level of several hundred mg / l, as represented by sewage, the concentration of suspended solids in washing wastewater that is periodically discharged from the filter is tens of thousands of mg / l. Very high concentration. Therefore, if you want to reuse the washing wastewater, in order to stabilize the processing performance in the separation process, the washing wastewater from the filtration process is temporarily stored and the quality of the water supplied to the separation process is not changed so much. It is necessary to return a predetermined amount little by little with a pump, and it is necessary to inject a new flocculant into the backwash wastewater to be returned, and to improve the recovery rate while reducing the scale of pretreatment equipment and reducing processing costs, It has been considered unrealistic.

  However, when the raw water is a primary treatment of sewage or factory wastewater, or when the concentration of suspended solids is relatively low, such as seawater or brine, the maximum water storage capacity of the raw water storage tank is determined. If the ratio of the amount of wastewater discharged in a single filter washing process is above a certain level, there is no need to adjust the amount of water drained from the cleaning wastewater. It has been found that the separation process can be performed relatively stably without an increase in concentration.

  In the present invention, in order to improve the recovery rate, the washing waste water of the separation step B including the filter is directly returned to the raw water storage tank, mixed with the raw water, and circulated as the feed water for coagulation sedimentation and coagulation pressure floating separation Use. At this time, the concentration of turbid substances in the raw water that can be relatively stably separated is preferably 10 mg / l or less, and preferably 5 mg / l or less. In addition, the ratio of the capacity of the raw water storage tank and the amount of drainage discharged in one filter cleaning process, [(raw water storage tank capacity) / (the amount of drainage discharged in one cleaning process)] is 5 or more. It is preferable that

  If the concentration of suspended solids in the raw water is not more than the above concentration, the concentration of suspended solids contained in the washing waste water of the filter can be suppressed to about several hundred mg / l. Furthermore, when the raw water storage tank capacity is more than 5 times the amount of drainage discharged in one washing process, the concentration of suspended substances in the separation process feedwater can be suppressed to 100 mg / l or less due to the dilution effect. Separation processing can be performed. More preferably, the capacity ratio should be 10 times or more. However, increasing the maximum water storage capacity of the raw water reservoir is not efficient because it only increases the scale of the facility, so it is limited to about 15 times at the maximum. Is preferred.

  The concentration of suspended solids in the raw water is determined by filtering the sample raw water using a glass fiber filter paper (GFP) having a pore diameter of 1 μm and a diameter of 50 mm, and drying the suspended substance trapped on the filter paper at 110 ° C. for 1 hour. The weight is measured and determined by the so-called GFP method, which is determined by subtracting the weight of GFP itself.

  In addition, when the washing wastewater of the separation step B including the filtration step is refluxed, in order to reduce the water quality fluctuation of the treated water in the separation step A, it is better to homogenize the water quality supplied to the separation step A, Therefore, you may install a stirring apparatus in a raw | natural water storage tank. The type of the stirring device is not particularly limited, but in addition to a stirring blade type such as a normal propeller or pitch paddle, an aeration stirring method or a simple baffle plate may be installed in the raw water storage tank.

  Furthermore, as a means of reducing the water quality fluctuation of the treated water in the separation step A, the amount of the flocculant injected in the separation step A is proportional to the suspended solids concentration temporarily increased at the time of reflux of the washing waste water in the filtration step. Increasing it is also effective. For this reason, it is also preferable to continuously monitor the turbidity of the feed water to the separation step A and control the injection amount of the flocculant in proportion to the turbidity. In this case, it is generally desirable to directly measure and monitor the suspended solids concentration. However, it is usually difficult to measure suspended solids concentration continuously, so continuous measurement using an integrating sphere scattering photometry method or the like is possible. Measure possible turbidity as an alternative indicator. Although there is no unambiguous correlation between suspended solids concentration and turbidity, turbidity and suspended solids concentration are limited but constant if it can be assumed that there is no significant change in the type of suspended solids. There is a proportional relationship. First, a calibration curve may be created by obtaining these relationships by trial operation or the like. The integrating sphere type scattered photometric method is measured based on the method defined in JIS K1010-9.4 (1998).

  In contrast to the present invention, when draining the waste water from the filter and the filtration process without refluxing as in the prior art, in addition to the sludge treatment of the coagulated sediment or the scum treatment of the coagulated pressure flotation, Separate wastewater treatment such as sludge separation and dehydration is required, and the scale of wastewater treatment associated with this process becomes large. There is a merit that the scale of wastewater treatment becomes very small because only the concentration sludge or the separation and dehydration of the floating scum is sufficient.

  Furthermore, in the present invention, when the cleaning wastewater in the filtration process is returned to the raw water, it is only necessary to return to the raw water storage tank as it is, and no special adjustment means such as a cleaning wastewater storage tank or a cleaning water reflux pump are required. There is also an advantage that is simplified.

  The treated water obtained in the above pretreatment step is treated by a reverse osmosis membrane in the latter stage, and is provided as reclaimed treated water in the case of raw wastewater, or fresh water (produced water) in the case of seawater or brine. Since the kind and model of a reverse osmosis membrane used here are suitably selected according to the purpose of use of raw water or treated water, they are not particularly limited.

  As a material for the reverse osmosis membrane, crosslinked aromatic polyamide, cellulose triacetate, and the like are suitable. As the type of reverse osmosis membrane, there are flat membranes such as spiral type and plate-and-frame type, and hollow fiber type modules, which are selected according to the application.

  According to the water treatment method and apparatus of the present invention, the recovery rate of treated water in the pretreatment process can be increased in wastewater reclamation or seawater or brine desalination, and the scale of pretreatment equipment can be reduced and the treatment cost can be reduced. In addition, it is possible to simplify and reduce the wastewater treatment equipment attached to this equipment, so that it is possible to expect an excellent effect of being able to operate efficiently and at low cost. .

  Below, the embodiment regarding the water treatment method and apparatus of this invention is described based on drawing.

  FIG. 1 is a schematic diagram showing a process flow used in the water treatment method according to the first embodiment of the present invention.

  In FIG. 1, 1 a is a coagulation-precipitation separation in which raw water and filtration process washing drainage reflux water are stored and mixed, and then a coagulant is added to grow a coagulation reaction and coagulation flocs and precipitate to obtain supernatant water as treated water. Step (separation step A), 2 is a filtration step (separation step B) for further clarifying the treated water, 3 is a reverse osmosis membrane separation step (separation) for obtaining regenerated treated water and fresh water from the filtered treated water Step C).

  First, the raw water 5 is once stored in the raw water tank 6, mixed with a filter washing drainage reflux water 15 to be described later, and then sent by the pump 7 to enter the aggregation reaction tank 9. In the agglomeration reaction tank 9, an appropriate amount of the aggregating agent 8 is added and immediately stirred with the raw water, so that the agglomeration reaction occurs uniformly and a part of the soluble substance contained in the raw water is insolubilized and deposited. At the same time, the suspended components are taken in and fine aggregates are formed in the raw water. At this time, in order to sufficiently perform the aggregation reaction, it is preferable to design the tank capacity so that the residence time of the raw water in the aggregation reaction tank is about 5 to 10 minutes. Moreover, it is preferable to provide a stirrer 10 in order to quickly diffuse the flocculant into the raw water. The type of agitator includes a propeller, a pitched paddle, a disk turbine, and the like, and can be appropriately selected depending on the properties of raw water.

  Next, the raw water in which the agglomeration reaction has occurred is transferred to the agglomeration tank 11, where it is stirred slowly, and the agglomerated fine particles collide with each other and combine to grow into large agglomerated flocs. In the agglomeration tank, in order to allow sufficient agglomerate to grow, the residence time is preferably about 3 to 10 minutes, and it is preferable to carry out slow agitation with an agitator 12 such as a disk turbine.

  The treated water which has been agglomerated as described above is sent to the subsequent sedimentation tank 13. In the sedimentation tank 13, the aggregated flocs settle and are separated into supernatant water (treated water 14) and aggregated sludge 16. Types of settling tanks include cross-flow settling tanks and center-driven settling tanks, and light torque type settling tanks, heavy torque type settling tanks, inclined plate settling tanks, and high-speed agglomeration depending on the sedimentation method of settling sludge. Although there are various types such as a sedimentation tank, the present invention does not limit the type of the sedimentation tank, and the size of the sedimentation tank is appropriately selected according to the properties of raw water and sedimentation sludge.

  In this way, the supernatant water (treated water 14) separated by coagulation and precipitation is sent to the subsequent filtration step 2. As described above, sand filtration is preferably used as the filtration method.

  About the sand filter 21, there are a single-layer filtration system and a multilayer (two-layer) filtration system depending on the type and configuration of the filter medium 22, and there are a gravity filtration system and a pressure filtration system depending on how filtration pressure is applied, Each is selected in combination with the quality of the feed water and the target quality of the treated water, but it is preferable to use a pressure type two-layer filter in consideration of the amount of filtered water and the stability of the water quality. Although there are various types of filter media, it is preferable to combine anthracite having an effective diameter of about 0.8 to 1.4 mm and silica sand of about 0.4 to 1.0 mm. The multi-layer filtration system is ideal for deep layer filtration, and a large amount of turbidity is trapped in the gap between the filter media. Therefore, it is difficult for the filtration differential pressure to rise, and the quality of the treated water is also good and stable. Become. Moreover, even if a filtration differential pressure | voltage rises as it is a pressure filtration system, there is no fall of the amount of filtrate water, and the stable amount of treated water can be ensured.

  Further, depending on the quality of the feed water, a multi-stage filtration system in which a sand filter is further provided after the pressure type two-layer filter may be adopted. In this case, since the main purpose of the subsequent sand filtration is to increase the clarity of the treated water, it is preferable to use a pressure type single-layer filter using quartz sand of about 0.3 to 0.4 mm.

  The filtration flow rate in the sand filter 21 is appropriately determined depending on the properties of the raw water and the type of the filter, and is not particularly limited. However, in the case of a normal pressure filter, the water flow rate is approximately It is selected within the range of 4 to 20 m / h, preferably 5 to 10 m / h. Further, the filtration time is also determined in detail depending on the raw aqueous state and the like, but is usually in the range of 20 to 24 hours in the case of a pressure type two-layer filter and 45 to 48 hours in the case of a pressure type single layer filter. It is preferable to set with.

  By the way, in the operation of the sand filter, the turbid components in the feed water are gradually accumulated in the filtered sand layer. Therefore, if the filtration operation is continued for a long time, the filtration pressure increases and the water quality decreases. For this reason, it is necessary to periodically perform backflow cleaning (backwashing) using filtered water to clean the filter medium. Usually, in the backwashing of the sand filter, a part of the filtered water stored in the filtered water tank 24 is pumped to the sand filter 21 by the pump 26 as the washing water 25. At this time, the direction of the flow of the washing water is opposite to that of normal filtration, and the washing waste water 27 containing a large amount of suspended matter trapped in the filter medium is discharged from the sand filter 21. The flow rate of the washing water is appropriately determined depending on the raw water state, the filter, and the type of the filter medium, similarly to the filtration flow rate, but the water flow rate is generally in the range of 30 to 50 m / h, preferably 35 to 40 m / h. Selected within.

  It is also preferable to use backwashing with air in addition to backwashing with filtered water. This is to send the air to the filter sand layer during backwashing to forcibly stir the filter media and make it easier to remove dirt from the filter media. It is appropriately selected depending on the type of filter medium.

  After backwashing as described above, the washing water in the filter is drained from the filter, and the supernatant water (treated water 14) after coagulation sedimentation is again supplied to the filter for filtration. The filtered water immediately after washing has to be rinsed for a certain period of time because many turbid components remain and the water quality deteriorates. The flow rate of the rinse water at this time is preferably equal to the flow rate during normal filtration operation because the operation is simple and the stability of the filtered water quality is also good. Moreover, it is preferable to set the rinse time in the range of 30 to 60 minutes.

  In the conventional process shown in FIG. 3, the washing waste water 27 and the rinse waste water 28 discharged from the filter are not drained from the apparatus and reused. In the present invention, the treated water in the pretreatment process is not used. In order to improve the recovery rate, these are returned to the raw water tank 6. As a method of refluxing, the washing waste water and the rinse waste water of the filter are returned to the raw water tank 6 as they are. At this time, in order to eliminate the load fluctuation of the coagulation sedimentation treatment and to stabilize the treated water quality, the raw water tank 6 is provided with a stirring means, and the washing waste water 27, the rinse waste water 28 and the raw water 5 which are returned to the raw water tank 6 are combined. It is also preferable to mix uniformly.

  The filtered water 23 that has been clarified through the above pretreatment process (flocculation sedimentation separation process and filtration process) and stored in the filtration water tank 24 is subjected to the reverse osmosis membrane separation process 3 (separation process C) by the high-pressure pump 30. ).

  At this time, in order to suppress a decrease in water permeability due to clogging of the reverse osmosis membrane module 32, the reverse osmosis membrane feed water 31 has a soil index SDI (Silt Density Index) of 4.0 or less, preferably 3.5. More preferably, the operating conditions such as the amount of flocculant added in the pretreatment step and the treatment flow rate should be adjusted as appropriate according to the properties of the raw water so that it is 3.0 or less. It is not limited.

  The reverse osmosis membrane feed water 31 is pressurized by the high pressure pump 30 to a pressure required for processing in the reverse osmosis membrane. The pressure at this time is set to an optimum value according to the concentration of evaporation residue of the feed water, the water temperature, and the recovery rate of the permeate 33 in the reverse osmosis membrane (the ratio of the permeate 33 to the feed water 31). For example, when the concentration of evaporation residue is about 200 to 5000 mg / l, which is not so high as raw water is sewage and primary wastewater from factory wastewater, the pressure is about 0.5 to 2.5 MPa. Although it is good, when it is as high as 5000 to 50000 mg / l such as brine or seawater, a high pressure of 3.0 to 7.0 MPa is required. However, in the present invention, as described above, the pressure is appropriately set according to the properties of the reverse osmosis membrane supply water, and is not particularly limited. The evaporation residue concentration is measured by a weight method according to JIS K0102-14.2 (1998).

  As described above, the reverse osmosis membrane module 32 has various types of materials, types, and the like, and the present invention is not particularly limited to these. However, the water permeability, desalting performance, and ease of handling are not particularly limited. From the viewpoint, it is preferable to use a spiral reverse osmosis membrane element made of a crosslinked aromatic polyamide.

  The reverse osmosis membrane module is usually configured by connecting one or a plurality of the above-described elements in series and storing them in a pressure vessel. The number of reverse osmosis membrane elements when connected in series is not particularly limited, but in order to suppress the deformation of the elements due to flow resistance and obtain permeate efficiently, the upper limit is about 8. Is preferred. Depending on the amount of treatment, a plurality of pressure vessels may be used in parallel, and depending on the raw water state, the concentrated water of the upstream reverse osmosis membrane module may be further treated by reverse osmosis membrane treatment and permeated water. It is also possible to increase the recovery rate.

  The recovery rate of the permeated water 33 with respect to the feed water 31 in the reverse osmosis membrane module is also determined by the properties of the raw water, particularly the concentration of evaporation residue, and is not particularly limited in the present invention. For example, primary treated water of sewage or factory wastewater When the recovery rate is about 200 to 5000 mg / l and not so high, the recovery rate is set in the range of 65 to 95%, preferably in the range of 70 to 90%. Moreover, when it is as high as 5000-50000 mg / l like brine or seawater, as a recovery rate, it is set in the range of 30 to 65%, preferably 35 to 60%.

  Finally, the permeated water 33 treated with the reverse osmosis membrane module is used after adjusting the pH, adding a bactericide such as chlorine, or adjusting the hardness component such as calcium according to the intended use. On the other hand, the concentrated water 34 of the reverse osmosis membrane module is concentrated and the concentration of evaporation residue is high, so it is difficult to return to the raw water as in the pretreatment process, and it is usually discharged and discharged from the apparatus as it is. The

  Next, a second embodiment relating to the water treatment method and apparatus of the present invention will be described based on the process flow of FIG.

  The second embodiment of the present invention is the same water treatment method as that of the first embodiment described above except that the coagulation sedimentation separation step of the pretreatment step is replaced with the coagulation pressure flotation separation step 1b (separation step A). is there. In the agglomeration pressure levitation separation step 1b, the treated water that has been agglomerated in the agglomeration reaction tank 9 and the agglomeration tank 11 is sent to the subsequent pressure levitation tank 17 as in the case of the first embodiment. In the pressurized levitation tank 17, the aggregated flocs adhere to the fine bubbles generated from the pressurized water 18 and float, and are separated into the treated water 14 and the floating scum 19. As the shape of the pressurized levitation tank, there are a rectangular shape and a circular shape, but the present invention is not particularly limited, and either one may be selected. Further, the pressurized levitation tank 17 generally has a scraper for scraping the levitation scum at the top. A pressurized water generator for generating fine bubbles is also provided. The pressurized water generator generally employs a method in which a part of pressurized floating treatment water is recirculated and compressed air is dissolved in this and injected into the pressurized floating tank. Any means can be used as long as it can generate bubbles, and any means may be used. Also, the size of the pressurized flotation tank is appropriately selected depending on the properties of the raw water and the settled sludge, and is not particularly limited.

  About the process after a cohesion pressurization floating separation process, it can process using the same method as above-mentioned 1st Embodiment, and it is not necessary to give a special process.

(Example 1 and Comparative Example 1)
A seawater desalination experiment facility based on the first embodiment of the present invention shown in FIG. 1 was manufactured and tested (Example 1). The main equipment / operating conditions and results of this experiment are shown below.
(1) Raw water ・ Type: seawater ・ Flow rate: 120 m ³ / day ・ Evaporation residue concentration: 35,000 mg / l
・ Suspension substance concentration: 3 mg / l
・ Raw tank capacity: 50m ³
(2) Flocculant Type: Ferric chloride (FeCl ₃ )
-Amount added: 10 mg / l
(3) Coagulation reaction tank ・ Inflow water amount: 130 m ³ / day ・ Volume: 0.4 m ³ (residence time: about 5 min)
(4) Coagulation tank ・ Inflow water amount: 130 m ³ / day ・ Volume: 0.8 m ³ (residence time: about 10 min)
(5) Sedimentation tank ・ Method: Center-driven sedimentation tank ・ Inflow water volume: 130 m ³ / day ・ Sedimentation area: 7 m ²
-Capacity: 20m ³ (Residence time: about 4h)
・ Aggregated sludge discharge amount: 0.4 m ³ / day ・ Treatment water flow rate: 129.6 m ³ / day (7) Filter ・ Filtration method: pressure type two-layer sand filtration method ・ Filter medium: anthracite (average particle size 0. 9mm) + silica sand (average particle size 0.5mm)
・ Inflow water amount: 129.6 m ³ / day ・ Filtration area: 0.57 m ²
-Filtration flow rate: 10m / h
・ Backwash frequency: Once every 24h
・ Backwash time: 30 min
・ Backwash flow rate: 30 m / h
・ Rinse time: 30 min
・ Rinse flow rate: 10 m / h
・ Washing wastewater (returned water amount): 10 m ³ / day (raw water tank capacity / washing wastewater ratio = 5)
-Concentration of suspended waste water (average): 148 mg / l
・ Treatment water flow rate (inflow water amount−wash waste water amount): 119.6 m ³ / day ・ Treatment water turbidity: <0.01 NTU
(8) Reverse osmosis membrane module ・ Supply water flow rate: 119.6 m ³ / day ・ Supply water pressure: 6.0 MPa
・ Reverse osmosis membrane type: 8 inch (0.20 m) × 1 m spiral element (Toray Industries, Inc .: TM820-370)
・ Number of reverse osmosis membrane elements: 5 ・ Pressure vessel: FRP: 8 inches × 5 m, 1 ・ Permeate (fresh water) flow rate: 47.8 m ³ / day ・ Permeate evaporation residue concentration: 200 mg / l
As a result of the seawater desalination experiment using the above equipment and operating conditions, the amount of treated water obtained from the separation step A (coagulation sedimentation separation step) for the inflow of raw water of 120 m ³ / day is the washing wastewater from the filtration step. Was refluxed to 129.6 m ³ / day, and the flow rate of treated water in the filtration step was 119.6 m ³ / day. Therefore, the recovery rate of the treated water combining the separation step A and the filtration step is
119.6 ÷ 120 × 100 = 99.7%
It became. In addition, as a result of operating the reverse osmosis membrane device at a permeate recovery rate of 40%, the obtained permeate flow rate was 47.8 m ³ / day, and the ratio of the permeate flow rate to the raw water inflow rate (total recovery rate) Is 47.8 ÷ 120 × 100 = 39.8%
Met.

  Moreover, the treated water quality of the obtained filter maintains a turbidity of 0.01 NTU or less even when the washing waste water of the filter is refluxed to the raw water, and a water quality equivalent to Comparative Example 1 described later is obtained. The osmotic membrane module was not clogged and the operation was stable.

In contrast, if no reflux washing drainage in the filtration step to the raw water tank (Comparative Example 1), to the raw water flow rate 120 m ^{3 /} day, treated water obtained from flocculation separation becomes 119.6m 3 ^/ day Furthermore, the treated water flow rate in the filtration step was 109.6 m ³ / day. Therefore, the recovery rate of treated water combining the separation process and the filtration process is
109.6 ÷ 120 × 100 = 91.3%
It became. In addition, as a result of operating the reverse osmosis membrane module at a permeate recovery rate of 40%, the permeate flow rate obtained was 43.8 m ³ / day, and the ratio of the permeate flow rate to the raw water inflow rate (total recovery rate) Is 43.8 ÷ 120 × 100 = 36.5%
Thus, only a low recovery rate was obtained as compared with Example 1 in which the washing waste water in the filtration process was refluxed. In addition, about the quality of the treated water of a filter, turbidity was 0.01 or less, and the stable operation of the reverse osmosis membrane module was possible.

(Example 2 and Comparative Example 2)
A factory wastewater reclamation experiment facility based on the second embodiment of the present invention shown in FIG. 2 was manufactured and tested. The main equipment / operating conditions and results of this experiment are shown below.
(1) Raw water ・ Type: Waste water from electronic parts factory (water after primary treatment)
・ Flow rate: 200 m ³ / day ・ Evaporation residue concentration: 2,000 mg / l
-Suspended substance concentration: 7 mg / l
・ Raw tank capacity: 100m ³
(2) Flocculant Type: Ferric chloride (FeCl ₃ )
-Amount added: 12 mg / l
(3) Coagulation reaction tank ・ Inflow water amount: 217 m ³ / day ・ Volume: 0.7 m ³ (residence time: about 5 min)
(4) Coagulation tank ・ Inflow water amount: 217 m ³ / day ・ Volume: 1.4 m ³ (residence time: about 10 min)
(5) Pressurized floating tank ・ Method: Center driven pressurized floating tank ・ Inflow water volume: 217 m ³ / day ・ Pressurized water flow rate: 30 m ³ / day (treatment water circulation)
・ Floating area: 3.2 m ²
・ Capacity: 7m ³
・ Floating scum discharge: 0.5 m ³ / day ・ Treatment water flow rate: 216.5 m ³ / day (7) Filter ・ Filtration method: pressure type two-layer sand filtration method ・ Filter medium: anthracite (average particle size 0. 9mm) + silica sand (average particle size 0.5mm)
・ Average influent water volume: 216.5 m ³ / day ・ Filtration area: 0.85 m ²
-Filtration flow rate: 10m / h
・ Backwash frequency: Once every 24h
・ Backwash time: 30 min
・ Backwash flow rate: 30 m / h
・ Rinse time: 30 min
・ Rinse flow rate: 10 m / h
・ Washing effluent (refluxing water): 17 m ³ / day (raw water tank capacity / washing effluent ratio = 5.9)
・ Washing wastewater suspended solids concentration (average): 254 mg / l
・ Treatment water flow rate (inflow water amount−wash drainage amount): 199.5 m ³ / day ・ Treatment water turbidity: <0.05 NTU
(8) Reverse osmosis membrane module ・ Supply water flow rate: 199.5 m ³ / day ・ Supply water pressure: 1.5 MPa
・ Reverse osmosis membrane type: 8 inch × 1 m spiral element (Toray Industries, Inc .: TM720-370)
・ Number of reverse osmosis membrane elements: 15 ・ Pressure vessel: FRP: 8 inches × 5 m, 3 ・ Permeate (fresh water) flow rate: 149.6 m ³ / day ・ Permeate evaporation residue concentration: 80 mg / l
As a result of experiments on seawater desalination using the above-mentioned facilities and operating conditions, the amount of treated water obtained from the separation step A (flocculation pressure flotation separation step) was obtained from the filtration step with respect to the inflow amount of raw water of 200 m ³ / day. The washing waste water was refluxed to 216.5 m ³ / day, and the treated water flow rate in the filtration step was 199.5 m ³ / day. Therefore, the recovery rate of the treated water combining the separation step A and the filtration step is
199.5 ÷ 200 × 100 = 99.8%
It became. Moreover, as a result of operating the reverse osmosis membrane module under the condition of a permeate recovery rate of 75%, the obtained permeate flow rate was 149.6 m ³ / day, and the ratio of the permeate flow rate to the raw water inflow rate (total recovery rate) Is 149.6 ÷ 200 × 100 = 74.8%
Met.

  Moreover, the treated water quality of the obtained filter maintains a turbidity of 0.05 NTU or less even when the washing waste water of the filter is returned to the raw water, and the water quality equivalent to Comparative Example 2 described later is obtained. The osmotic membrane module was not clogged and the operation was stable.

In contrast, if no reflux washing drainage in the filtration step to the raw water tank (Comparative Example 2), to the raw water flow rate 200 meters ^{3 /} day, the amount of treated water obtained from the agglomeration floatation on separation step 199.5M ³ In addition, the treated water flow rate in the filtration step was 182.5 m ³ / day. Therefore, the recovery rate of treated water combining the separation process and the filtration process is
182.5 ÷ 200 × 100 = 91.3%. Further, as a result of operating the reverse osmosis membrane module under the condition of a permeate recovery rate of 75%, the obtained permeate flow rate was 136.9 m ³ / day, and the ratio of the permeate flow rate to the raw water inflow rate (total recovery rate) Is 136.9 ÷ 200 × 100 = 68.4%
As a result, only a low recovery rate was obtained as compared with Example 2 in which the washing waste water in the filtration process was refluxed. In addition, about the quality of the treated water of a filter, turbidity was 0.05 or less, and the stable operation of the reverse osmosis membrane module was possible.

  The water treatment method and apparatus of the present invention can be effectively used for water treatment such as recycling of wastewater such as sewage and industrial wastewater and desalination of seawater or brine.

The schematic diagram which shows the water treatment method and apparatus which concern on the 1st Embodiment of this invention. The schematic diagram which shows the water treatment method and apparatus which concern on the 2nd Embodiment of this invention. The schematic diagram which shows an example of the conventional water treatment method and apparatus.

Explanation of symbols

1a ... Coagulation sedimentation separation process (separation process A) based on the present invention
1b: agglomeration pressure flotation separation step (separation step A) according to the present invention,
1c: Conventional coagulation sedimentation separation process,
2 ... Filtration process (separation process B)
3. Reverse osmosis membrane separation process (separation process C)
4 ... Filter washing waste water treatment process 5 ... Raw water 6 ... Raw water tank 7 ... Raw water pump 8 ... Coagulant 9 ... Coagulation reaction tank 10 ... Stirrer 11 ... Coagulation tank 12 ... Stirrer 13 ... Precipitation tank 14 ... Treated water 15 ... Filter washing waste water reflux water 16 ... Coagulated sludge 17 ... Pressure floatation tank DESCRIPTION OF SYMBOLS 18 ... Pressurized water 19 ... Levitation scum 20 ... Filtration pump 21 ... Sand filter 22 ... Filter medium 23 ... Filtration water 24 ... Filtration water tank 25 ... Washing water 26 ... Wash pump 27 ... Wash drain 28 ... Rinse drain 30 ... High-pressure pump 31 ... Reverse osmosis membrane feed water 32 ... Reverse osmosis membrane module 33 ... Reverse osmosis membrane permeate 34 ... Reverse osmosis membrane concentrated wastewater 40 ... Filter washing waste water sedimentation tank 41 ... Filter washing waste water treated water (drainage)
42 ... Aggregated sludge

Claims (12)

After the raw water is temporarily stored in the raw water storage tank, the separation step A in which the agglomeration pressure flotation separation and / or the aggregation precipitation separation is performed, the separation step B in which the treated water obtained in the separation step A is filtered, and the separation step B A water treatment method comprising a separation step C for separating the obtained treated water by reverse osmosis membrane to obtain permeate, wherein the separation step B has a washing step, and the washing wastewater generated in the washing step is used as the raw water A water treatment method characterized by returning to a water storage tank. The ratio between the capacity of the raw water storage tank and the amount of drainage discharged at one time in the washing step is
(Raw water storage tank capacity) / (Drainage discharged at once in the cleaning process) ≧ 5
The water treatment method according to claim 1, wherein the relationship is satisfied. The water treatment method according to claim 1 or 2, wherein the separation step B is single-stage filtration by two-layer filtration. The water treatment method according to claim 1 or 2, wherein the separation step B is multi-stage filtration in which two-layer filtration is performed in the former stage and single-layer filtration is performed in the latter stage. The water treatment method according to any one of claims 1 to 4, wherein the addition amount of the flocculant in the separation step A is controlled in proportion to the turbidity of the water supplied to the separation step A. The water treatment method according to any one of claims 1 to 5, wherein the concentration of suspended solids contained in the raw water is 10 mg / l or less. The water treatment method according to any one of claims 1 to 7, wherein the raw water is a primary treatment of sewage or factory wastewater. The water treatment method according to claim 1, wherein the raw water is seawater or brine. Separation means A provided with a raw water storage tank and a coagulation pressure flotation separation device and / or a coagulation sedimentation separation device provided at the subsequent stage of the raw water storage tank, and a filter provided at the subsequent stage of the separation means A A separation means B provided, and a separation means C provided with a reverse osmosis membrane separation device provided at a subsequent stage of the separation means B, wherein the separation means B collects the washing wastewater generated by the washing of the filter. A water treatment apparatus comprising means for returning to the raw water storage tank. The water treatment device according to claim 9, wherein the type of the filter is a two-layer filter. The water treatment apparatus according to claim 9, wherein the filter is configured such that a two-layer filter is disposed in the front stage and a single-layer filter is disposed in the rear stage. An injection pump for injecting the flocculant into the water supplied to the coagulation pressure flotation separation device and / or the coagulation sedimentation separation device, and a control for controlling the injection amount of the coagulant in proportion to the supply water turbidity of the separation means A The water treatment device according to any one of claims 9 to 11, comprising a device.

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