JP2006136753A - High pressure type fine sand filter and filtering method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high pressure type fine sand filter adaptable to a conventional pressure type filtering method, capable of inexpensively obtaining safe and palatable water corresponding to cryptosporidium without injecting chemicals and capable of being also utilized in the pretreatment of ultrapure water or the purification of industrial water, and a filtering method using it. <P>SOLUTION: The amount of backwashing water is reduced by filling a filter with 0.2-100 cm of fine sand with an effective particle size of 0.02-0.2 mm as filter sand and performing filtration so that filtering loss head immediately before backwashing becomes a high pressure of 2-40 m without adding a flocculant. By increasing a filtering speed to 30-500 m/day, the amount of filtered water per unit area is increased. Since no flocculant is used and raw water can be biologically treated if it contains organic matter, safer filtered water can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to muddy water treatment for obtaining purified water from raw water such as river surface water, lake water, dam water, and groundwater. More specifically, it relates to medium-to-high-speed filtration from clear raw water to slightly contaminated raw water, and relates to water purification treatment that makes raw water safe and delicious drinking water. Furthermore, in addition to purified water, it relates to the production of ultrapure water, industrial water purification, and advanced treatment of wastewater treatment water.

  The main water purification methods are rapid filtration and slow filtration. However, the former is basically maintained and managed by an operator, but there is a disadvantage that personnel cannot be allocated in a small scale. Aluminum was newly added to the water quality standards for tap water, and strict flocculant management was required. This is severe for small-scale rapid filtration. In addition, the odor of filtered water has increased due to the deterioration of raw water, and the number of places where advanced treatment such as ozone treatment has been increased. However, the biggest drawback of advanced processing is that it increases costs.

  Slow filtration is performed in relatively clean raw water, but the low filtration rate is 4-5 m / day, and the river surface water and lake water cause clogging of the sand layer. Cost is not cheap.

  Cryptosporidium is a major problem. This protozoa is 5 μm in size and can be removed by filtration, but it cannot be killed by chlorine. Therefore, the conventional direct feed system using tap water just by disinfecting well water and underground water has been reviewed. These groundwaters are characterized by low organic matter and low turbidity. There is an idea that rapid filtration or slow filtration for water that is contaminated to some extent is not appropriate in terms of complexity of maintenance and cost in order to replace the direct delivery method.

  Recently, membrane filtration has attracted attention. Membrane filtration can be used when the raw water turbidity is extremely low, and fully automatic operation is the greatest merit. In particular, there is an idea that membrane filtration is suitable for removing relatively large particles such as Cryptosporidium with a small amount of organic matter. However, the biggest problem is the complexity and cost of maintenance. Although it is fully automatic, pre-treatment is often required as a real problem, and there are many troubles such as backwashing of membranes and chemical cleaning. Therefore, the big problem that cost is very high has generate | occur | produced.

  One of the important things in a globalized society is cost reduction. The water supply, which is a social capital, has to match this. The above three methods have a cost disadvantage. Cost reduction is extremely important, especially when the local government is small or the water supply population is small.

As a new filtration method, a fine sand filtration method as described in Patent Document 1 has been developed.
In the fine sand filtration method described in Patent Document 1, the use of fine sand eliminates the need for a flocculant in rapid filtration, and can significantly reduce off-flavor by causing biological treatment. Furthermore, by using the sand for slow filtration as fine sand, there was no leakage of turbidity, and the filtration rate could be increased. In addition, the introduction of a backwash device eliminates the need for sand removal as a measure against clogging of sand.

  Membrane filtration increases as membrane clogging repeats backwashing, and finally the membrane module must be replaced.However, in fine sand filtration, the fine sand layer is completely regenerated by backwashing. No degradation occurs.

  However, the fine sand filtration method increases the number of backwashing times when the raw water turbidity is high. During heavy rain, the proportion of filtered water used for backwashing increases. Although the water purification treatment can be temporarily stopped as in membrane filtration, the supply of filtered water is stopped during that time.

  In addition to tap water, clarification filtration has demands from many places such as ultrapure water production, industrial water filtration, and industrial wastewater treatment advanced filtration. The production of ultrapure water is indispensable for the electronics industry, but usually uses industrial water, groundwater, etc. as raw water. It is necessary to remove turbidity, fine dust, iron, and the like as filtration. However, since the addition of chemicals affects the subsequent treatment, an additive-free treatment is desired.

  In addition, industrial water is desired to produce the same inexpensive and safe water as water purification, but there is no appropriate method. For example, in the tofu manufacturing and bean sprouts manufacturing industry, tap water has a problem of water quality and is expensive. Inexpensive water from which Cryptosporidium has been completely removed is desired, but its supply is never easy.

  Wastewater from factory wastewater is to be recycled if possible. Wastewater treated water cannot be recycled without further advanced treatment and advanced filtration, but it has problems in terms of ease of maintenance and cost.

  In the case of slow surface filtration and rapid filtration, in the case of river surface water, muddy water suddenly flows in during heavy rain, which is a problem. This is one of the reasons why membrane filtration is practically unusable. Unmanned operation is difficult to cope with such a sudden change in turbidity, which causes a cost increase.

Membrane filtration filters inorganic turbidity. Although it is backwashed once every 30 minutes to 1 hour, it will eventually be blocked and backwashing will be required. Membranes that do not occlude and that can withstand organic contamination have not been developed. In practice, use is limited to groundwater. When using it for river surface water, pretreatment close to water purification is required. In any case, it is a special high-cost system.
JP 2003-275882 A

  Rapid filtration adds a flocculant, but has a problem of chemical-free treatment. Membrane filtration usually uses flocculants and chlorine, but we decided not to use chemicals to make safe and delicious water. Not using chemicals indicates that biofiltration is performed. Therefore, it becomes more advanced water purification treatment.

  Speaking of biological filtration is slow filtration, but the problem is to increase the filtration rate. In slow filtration, if the filtration rate is increased, turbidity leaks and clogging occurs frequently, and operation is not possible.

The development of a system for filtering groundwater as a countermeasure against Cryptosporidium is an issue. A construction method and a maintenance cost are low, and a method suitable for small-scale water supply is desired.
Fine sand filtration has the advantage of biological filtration as well as physical filtration with no chemical filtration, and it is a challenge to develop a processing method with high capacity based on this. In particular, when the raw water turbidity is high, the number of backwashes increases rapidly in fine sand filtration. The challenge is to reduce the number of backwashes. If this is possible, filtered water can be obtained even when the river is muddy. Rapid filtration can cope with bending by increasing the amount of flocculant, but other existing methods are impossible.

In fine sand filtration, if the fine sand was made smaller, the filtration loss head increased and there was a limit. The challenge is to further expand this limit.
Fine sand filtration is good for removing turbidity when using biological treatment, but if the organic substance is mainly composed of a small amount of organic matter in the raw water, the filtration performance decreases. Especially in the case of river surface water, contaminated water mainly composed of inorganic turbidity flows during heavy rain or rice planting. In such a case, the construction of a system that can be sufficiently removed only by physical sieving is a problem.

  Membrane filtration is characterized by being smaller than other methods even with the same amount of filtration. Pressure type rapid filtration is downsized with a method without a coagulation sedimentation basin, but basically follows gravity type filtration and has its limits. It is a problem to provide a pressure-type filtration system without chemicals, and to provide filtered water that is smaller, safer and cheaper.

Membrane filtration involves backwashing and chemical cleaning, and finally requires membrane replacement. It is a problem to provide a technology for changing to a membrane that does not require chemical cleaning or replacement of the filter medium, such as a membrane.
There was no suitable method for pretreatment of ultrapure water production or filtration of industrial water, but it is a problem to provide this.

  If there is an automatic filtration system that can easily remove most of the turbidity as a pretreatment for slow filtration and rapid filtration of river surface water and dam water, there is a possibility that the load will be reduced and the maintenance cost will be greatly reduced. . If used as a pretreatment for membrane filtration, it may be applicable to river surface water. The challenge is to provide these pretreatment systems.

  An object of the present invention is to provide a high-pressure fine sand filtration device and a method for solving such problems.

  The high pressure fine sand filter according to claim 1 of the present invention is a fine sand filter for filtering raw water such as rivers, lakes, groundwater, and industrial wastewater treated water. The effective diameter of fine sand or garnet is 0.02 to 0.2 mm and the average diameter is 0.25 mm or less, 0.2 to 100 cm of filtration sand is filled, and the filtration rate is 30 to 500 m / day. A pump for supplying the raw water and a pump for backwash regeneration with a backwash speed of 10 to 400 m / day are provided. It is characterized by having pressure resistance and a pressure detection instrument for efficient filtration by increasing to 40 m.

  The high pressure fine sand filtration device according to claim 2 is provided with a surface cleaning pipe for cleaning the fine sand or garnet surface or a grit for loosening the surface, and complements backwashing.

  The high-pressure fine sand filtration device according to claim 3 is characterized in that the timing of backwashing is detected by a timer or a filtration loss head and the operation is completely automated.

  The high pressure fine sand filtration method according to claim 4 is a fine sand filtration method for filtering raw water such as rivers, lakes, groundwater, and industrial wastewater treated water. Or a facility for supplying the raw water with a garnet of 0.2 to 100 cm and a filtration rate of 30 to 500 m / day, and a backwash facility for backwash regeneration with a backwash rate of 10 to 400 m / day It is characterized by having pressure resistance and pressure detection equipment for efficient filtration by increasing the filtration loss head to 2 to 40 m when filtration is finished and switching to backwash operation.

  The high pressure fine sand filtration method according to claim 5 is provided with a mechanism for cleaning or loosening the surface for cleaning the fine sand or garnet surface, and complements backwashing. The high pressure fine sand filtration method according to claim 6 is characterized in that the backwashing timing is detected by a timer or a filtration loss head and the operation is completely automated.

  The basis of the present invention is high-pressure pressure filtration. Traditionally, pressure filtration is a variation of rapid filtration, but there is little benefit from simply replacing gravity with pressure. Therefore, using fine sand, we examined in detail whether the filtration pressure (filtration loss head) could be removed from the conventional range. The filtration head loss, sand particle size, and filtration rate were independent but correlated. Although the filtration loss head has a correlation with the filtration rate, the inventors have invented a system that enables a high pressure region exceeding the conventional limit.

  Conventionally, what is called a pressure sand filter is a micro floc method using a flocculant or a chemical injection filtration method. Basically, it follows the conditions of gravity-type rapid filtration. In fact, the Japan Water Works Association design guidelines stipulate that the number of ponds, filter layer, and cleaning method are the same as those for gravity filtration ponds. Also, in the pollution prevention manager's text “Pollution Prevention Technology and Regulations-Water Quality Edition” (5th edition, Maruzen), the mechanism is exactly the same except for the way pressure is applied. The effective diameter is 0.5 to 0.7 mm, the uniformity coefficient is 1.7 or less, and the thickness of the filter layer is 500 to 700 mm. About filtration loss head, it becomes backwashing when it becomes 1.5-2m. Filtration rates are 120-150 m / day, although recent studies have allowed 200 m / day.

  The filtration conditions for rapid filtration are that the turbidity may leak if the filtration rate is too high, and the filtration loss head increases as the filtration progresses, but at the same time the filtration water turbidity gradually increases. There is. So-called water path is made. Therefore, the upper limit of filtration loss head is 1.5-2 m / day. This is a condition of conventional gravity rapid filtration and also a condition of pressure sand filtration. Slow filtration has also followed this value.

  The present invention is greatly characterized in that the upper limit of pressure (loss head) for filtration is eliminated. According to Example 7 described later, when fine sand having an effective diameter of 0.1 mm, a uniformity coefficient of 1.3, and an average diameter of 0.125 is used, it has been found that there is no problem even if the filtration loss head is 40 m. . This was a new discovery that was completely unthinkable from the conventional facts and perceptions. This is because the retention of filter turbidity was greatly increased by using fine sand. Furthermore, by not using a flocculant, the fluidity of the turbidity itself is lowered, which is due to the suppression of leakage under high pressure. In the case of sand of about 0.3 mm, there was a tendency for turbidity to flow out slightly with high-loss heads.

  We did not experiment with more head loss, but the upper limit is presumed to be higher. However, if considering the practical meaning, when considering the cost and power cost of the pressure vessel, 40 m or less is appropriate.

  An appropriate filtration rate is 30 to 500 m / day. Although there is no lower limit of the filtration rate, considering the practical limit, it will be necessary to show performance several times that of slow filtration. The upper limit needs to be determined by experiment, but according to Example 4, it can be 400 m / day or more. However, although it is slight, the turbidity of filtered water tends to increase. Such speeding-up by filtration using sand has not been considered in the past. It became possible for the first time with no drug injection and high pressure.

  The particle size of the fine sand is in the range of effective diameter 0.02-0.2 mm. The fine sand particle size may be slightly larger in the case of river surface water with organic matter pollution, but the effective diameter is about 0.1 mm or less in the case of inorganic turbidity with little organic matter such as some groundwater. It is preferable to use fine sand.

  Since sand is greatly affected by the particle size distribution, it cannot be defined by an effective diameter of only 10% from the smallest, but the size of turbidity that can be removed by physical clogging and sieving effect is basically this definition. It is greatly affected. Although the minimum effective diameter was set to 0.02 by experiment, the filtration rate was greatly reduced. This decrease can be dealt with by pressurization.

  As shown in Examples 1 to 4, the maximum effective diameter was set to 0.2 mm. In the experiment with an effective diameter of 0.17 mm, the result of sieving filtration at the start of the experiment was poor, and 4 weeks passed after the start. This is because it took time to start up, as biofilms finally formed. This area is the upper limit of fine sand. For inorganic turbid substances, the effective diameter is 0.15 mm or less.

  According to the gravity filtration experiment, when using 0.15-0.25mm sand, turbidity leaks when the filtration speed is high, and the turbidity removal rate is 90% at 150m / day. Declined. In addition, the initial filtration loss head increased and there was a limit to practical use. In the case of the gravity type, in the filtration of inorganic matter, turbidity leaks when the filtration rate increases. When trying to use smaller fine sand, the filtration loss head was high and quickly clogged, making it impossible to operate. That is, when the turbidity is biased to mineral, fine sand filtration has been considered to have essential problems in terms of filtration speed, turbidity leakage, and filtration loss head.

  However, when a high-pressure filtration experimental device was constructed and the experiment was repeated, when inorganic turbid filtration was performed using fine sand with small sand, there was no turbidity leakage, and the initial filtration loss was not clogged. It was found that the water head is high and only rises with filtration. From this, the fine sand filtration system showed a new development. The fact that there is no leakage of turbidity at high pressure and that inorganic turbidity can be filtered by high-pressure filtration has overturned conventional common sense. This is the importance of the present invention.

  The fine sand filtration system represented by Patent Document 1 has become an invention that exceeds the conventional technical common sense that the use of fine sand has a high filtration rate and does not require a flocculant. Although the present invention is based on the fine sand filtration system, there is no leakage of turbidity even when the filtration head loss exceeds 2 m, no rapid rise with loss water, smaller fine sand. If it chooses, it discovered that it could cope with inorganic turbidity, and came to systematize.

  The uniformity coefficient is a ratio of 60% of the particle diameter to the effective diameter, which is fractionated from small sand, and is usually about 1.3 to 2. However, this alone is not adequately defined as long as the sand distribution has various spreads. Therefore, the average diameter is assumed not to exceed 0.25 mm. This is because the sand section of 0.2 to 0.3 mm is maximized. In other words, it is a condition that sand of 0.3 mm or more hardly exists as filtered sand. If present, it will have the meaning of supporting sand.

  If the sand is small, the structure of the supporting sand layer becomes difficult unless a certain particle size distribution is recognized practically. For example, it is particularly appropriate to use sand containing fine sand such as 0.02 to 0.15 mm (the sand mainly composed of 0.1 mm or less is called fine sand). However, when the backwash speed is set such that the minimum sand does not flow out, the sand of about 0.1 to 0.2 mm becomes the supporting fine sand. In this case, it is doubtful whether the definition of effective diameter 0.02 mm and uniformity coefficient 6 is meaningful. Therefore, in the present invention, the effective diameter and the average particle diameter of sand for filtration are defined.

  The smallest sand size among the fine sands was examined. First is the range of fine sand. The smaller the fine sand, the better, but the condition is that it does not flow out during backwashing. Although there is a relationship between the backwash speed and the particle size, it is important to first distinguish between mud and fine sand, and according to the experimental results, the classification is 10 μm. The average particle diameter is 20 μm, that is, 0.02 mm as a particle diameter for further clarifying the division.

  The upper limit of Cryptosporidium physical sieving is 99% for fine sands of sieving sections 0.15 to 0.25, according to experiments. According to Example 5, when the effective diameter was 0.076 mm and the average diameter was 0.1 mm, the removal rate of turbidity of 2 to 3 μm was 98.9%, and the removal rate of turbidity of 3 μm or more was 100%. That is, Cryptosporidium can be completely removed.

  In the present invention, even if the upper limit of the pressure (loss head) required for the filtration is high, the fine sand does not solve the problem. In this case, it is necessary to reduce the thickness of the fine sand layer. In Example 5, the thickness is suitably 1 to 3 cm because of economic restrictions considering the filtration loss head. It can be inferred that the lower limit of the fine sand having an average diameter of 0.02 mm is that the filtration layer has a thickness of 1 mm or less, and the filtration loss water head rapidly increases and can be filtered. In this case, considering the ease of backwashing, the thickness is 2 mm or more. Thus, it is also the basis of the present invention to make the filtration layer thinner as the fine sand becomes smaller.

  The filtration sand thickness is 0.2 to 100 cm. It seems that the range is very wide because the sand particle size may be large or small. In the case of large fine sand, it is a very common story that the sand layer is up to 100 cm.

  The backwash speed varies depending on the size of the fine sand. Sand with an effective diameter of 0.02 mm can be fluidized even at 10 m / day. Example 6 shows the standard. It is determined appropriately depending on the particle size of sand and the nature of raw water within a range of about 10 to 400 m / day.

  The problem at the time of backwashing is not only the backwashing speed but also how to separate the turbidity and fine sand to be backwashed. In the case of river surface water and river water, it was confirmed by experiments that separation is often difficult at a backwash speed of 100 m / day or less. Therefore, in the case of fine sand, particularly when the particle size is small, it is used only when there is no large turbidity such as groundwater. Speaking of the average sand particle size, it is generally about 0.1 mm or less. Fine sand filtration was made possible by limiting the use of fine sand filtration to raw water containing large turbidity.

  In the case of river surface water, if the average particle size of fine sand is about 0.1 mm or less, fine sand may flow out if turbidity is washed away by backwashing. It is preferred to remove turbidity.

  In order to improve the separation of fine sand and turbidity, it is convenient for fine sand filtration to use a filter medium with a large specific gravity such as garnet. The specific gravity of sand and garnet is 2.7 and 3.5, respectively. The ratio of the settling speed is proportional to the difference from the specific gravity of water, and is 1.7: 2.5. That is, in the case of the same particle size, the maximum backwash speed can be increased by 47%, so that separation from turbidity becomes easier. Two-layer filtration with garnet as the lower layer and sand as the upper layer is also preferred.

  Anthracite is one of the filter media used for filtration. This is slightly disadvantageous because the specific gravity is smaller than that of sand, and is difficult to use as fine sand. In addition, various artificial filter media have been developed. Of course, any filter media having the same particle size as fine sand or fine sand can be used as it is in the present invention. There are no points to be noted other than specific gravity.

  It describes about filtering an inorganic turbidity by a non-flocculating agent. In the present invention, the use of small fine sand, that is, fine sand, is extremely effective even when there is no flocculant and no biofilm. For example, high-pressure fine sand filtration only by sieving fine sand having an average diameter of about 0.1 mm with respect to groundwater that does not easily generate biofilm and has neither organic matter nor iron is practical as a countermeasure against Cryptosporidium. It is also suitable for filtration containing disinfectants such as chlorine.

  Inorganic turbid filtration using fine sand may be considered to correspond to an MF membrane because it is a pressure type and sieve filtration. The difference is that the MF membrane is a single membrane whereas the fine sand filtration is a three-dimensional filtration. Therefore, membrane filtration may break, but fine sand filtration does not have it, and there is a big difference in the amount of retained turbidity. Backwashing is an incomplete MF membrane, while fine sand filtration is completely restored. In addition, although the membrane is vulnerable to organic pollution, the fine sand is covered with a biofilm and is expanded, and the water loss may be reduced and the water quality may be improved. Thus, the present invention can be regarded as a system that exceeds the MF membrane.

  Most raw waters produce microorganisms in the sand. If filtration is continued, a biofilm (filtration membrane) will be generated and adsorb turbidity. Therefore, a flocculant is unnecessary even when the size is slightly larger with fine sand. In addition, by using no flocculant, filtration water quality is improved by biological filtration. This feature is the same not only in gravity type fine sand filtration but also in the present invention.

  The present invention is basically provided with a device for unwinding the sand surface by surface cleaning or grit lattice during backwashing. Even turbidity that does not have much cohesion gradually becomes a mudball-like one. In the case of turbidity with particularly high cohesiveness, an air cleaning device may be laid.

  Filtration includes constant pressure filtration and constant flow filtration. In principle, constant flow filtration is used in the present invention. If the pressure is increased by constant pressure filtration, the initial flow rate becomes extremely large and turbidity leaks out. However, constant flow filtration does not need to be strictly controlled. It is the present invention that can withstand flow rate fluctuations. When the filtration is started, the low filtration loss head is gradually increased to a high filtration loss head. It is a standard method to determine the backwash timing by detecting this filtration loss head. Timer control can also be used.

  The high pressure fine sand filtration apparatus and method of the present invention can provide safe drinking water from various raw waters. In organic matter and river water and dam water with a lot of turbidity, turbidity and dissolved organic matter and off-flavor can be removed. In the gravity method, the frequency of backwashing becomes high, and even when the yield of purified water from raw water decreases, high yielding operation becomes possible. For organic matter such as groundwater and raw water with low turbidity, water can be purified using the sieve filtration effect by making the fine sand particle size small. This is a low-cost technology that replaces the MF membrane. It is useful as a countermeasure against groundwater cryptosporidium. The system is useful as a pretreatment for membrane filtration, rapid filtration, and slow filtration. By using this as a pre-treatment, maintenance and management are greatly facilitated, leading to a cost reduction. The present invention is not only used for water purification itself, but also useful for pretreatment of ultrapure water, purification of industrial water, or recycling of wastewater treatment water. In particular, since the filtration does not add chemicals, there is a great advantage in subsequent processing and water utilization.

Embodiments of the present invention will be specifically described below with reference to FIGS.
FIG. 1 is an explanatory view of a typical high pressure fine sand filter. The raw water taken by the intake pump 1 and put in the landing tank 2 is put into the high pressure fine sand filtration tank 4 by the raw water pump 3 through the raw water valve 14. In the high pressure fine sand filtration tank 4, there are a filter sand 10, a supporting sand layer 9 and a supporting gravel layer 8 below the surface cleaning device 11, and a water collecting device 7 at the bottom. The filtered water from the water collecting device 7 is sent from the filtered water valve 18 to the water purification tank through the washing water tank 5 and becomes the filtered water 6. The filtration loss head is detected by a differential pressure gauge 19. When the differential pressure gauge detects a predetermined pressure, the backwash mode is entered. The backwash pump 13 is activated, the surface washing valve 16 and the bottom backwashing valve 17 are opened, and backwashing is started. The backwash drainage is discharged through the backwash drain valve 15. The internal air is removed by the air venting device 12.

  The flow rate adjustment is made constant by the raw water pump 3 or a flow rate adjustment valve provided separately. The filtration loss head is low at the start of filtration and is several times to 10 times before backwashing. Therefore, complete control is more preferable, and it is a fact that there is a limit to the constant flow rate in the constant flow valve and gate valve adjustment. However, even if the flow rate increases by about 50%, there is no particular problem, so an inexpensive method can be used.

  The laminated height of the fine filter sand is 0.2 cm or more in the case of fine sand, and the sand becomes thicker as the average diameter of the fine sand increases, but the maximum is about 100 cm. When the filtration loss head is set high, it is desirable to make it slightly thicker. This is to disperse the pressure.

  The filtration rate is in the range of 30 to 500 m / day, and the effective diameter of fine sand is 0.02 to 0.2 mm. When used as a pretreatment, the filtration rate is high and the effective diameter of fine sand is also large. On the contrary, when it is just purified water, the filtration rate is low with small sand. The sand particle size and filtration rate are also affected by the organic matter concentration of the raw water. When the organic substance concentration is low, fine sand is preferable, and a high loss head is used, and the filtration rate is slightly low. In particular, turbidity is low in groundwater, and when used as a countermeasure against Cryptosporidium, the average sand diameter is preferably about 0.1 mm or less.

  The filtration loss head immediately before backwashing is in the range of 2 to 40 m, but 3 m or more is preferable for taking advantage of the characteristics. For example, when the effective diameter of fine sand is 0.17 mm, the filtration rate is 100 m / day, the maximum filtration loss head is 10 m, and the surface water of the river basin is filtered. The gravity type fine sand filtration is operated at 50 m / day. Compared with the case, the filtrate water obtained by the next backwash was 4 to 8 times. Therefore, the ratio of the amount of backwash water to the amount of filtration decreases, so it can be applied to raw water that has a sudden change in turbidity like river surface water.

  Backwashing is basically to loosen the fine sand surface. At the surface water level of the river, the filter membrane on the sand surface has a weak binding force, so it is normal to use a weak surface wash. The surface washing water amount may be about 20% of the bottom back washing amount. Air cleaning is not required unless it is sticky turbid.

  At the time of backwashing, in rapid filtration, the expansion rate of sand is about 30%, but it is preferably higher than that and may exceed 200%. The backwash speed is determined by the size of the fine sand and the nature of the raw water. In the river surface water, the fine sand is slightly larger, and it may be necessary to distinguish it from fine garbage.

  FIG. 2 shows an example of two-stage high pressure filtration of river surface water. In the first stage, most of the turbidity is removed, and in the second stage, filtration is performed mainly using biological treatment. The raw water taken from the upstream intake pump 20 enters the upstream landing tank 21. The raw water is put into the pre-stage high pressure fine sand filtration tank 23 by the pre-stage raw water pump 22 and filtered through the pre-stage fine sand filtration layer 24. The filtered water is put into the pre-cleaning tank 27. Backwashing is performed using the front-stage backwash pump 26, and backwashing is performed using the front-surface cleaning device 25 and the bottom backwashing device. The filtered water from the upstream washing tank 27 is subjected to the subsequent filtration. The subsequent processing is the same as in FIG. Two-stage filtration can produce high quality filtered water that is always stable against changes in river turbidity. In river water, turbidity rises rapidly during heavy rain, and in the gravity type, the number of backwashes increases significantly. For this reason, the amount of backwash water increases, and only a small amount of filtered water may be obtained. By adopting a high-pressure type, the number of backwashing operations is reduced, the amount of backwashing water is greatly reduced, and the amount of purified water is the same as that in fine weather. Since the latter stage basically has few backwashing times, the high pressure type can be replaced with a gravity type.

  Thus, by placing a high-pressure fine sand filter as a pretreatment in the previous stage, a stable amount of purified water can be obtained even when turbidity is high. It is also a notable advantage that this system is automatic and does not require an operator. Conventionally, there has been no suitable method for water purification facilities for small to medium-sized river surface water, but the present invention responds to this.

  Next, the present invention will be described in more detail by way of examples.

  In the plant of the high pressure type filtration apparatus as shown in FIG. 1, fine sand having an effective diameter of 0.17 mm and a uniformity coefficient of 1.8 was used as filtration sand, and 50 cm was filled and started up. At the time of start-up, that is, at the stage where a filtration membrane (biofilm) is not generated, river surface water having an average turbidity of 1.1 degrees was filtered. The filtration was started at a filtration loss water head of 0.7 to 5 m and a filtration rate of 100 m / day. The result was a filtration time of 19 hours, and the filtered water turbidity was 0.2 to 0.23 degrees except for the initial 3 hours. Even when the filtration loss head was close to a very high value of 5 m, the filtrate turbidity did not increase.

  As a result, the turbidity removal rate was not high, but extremely important data was obtained in the following two points. First, the initial filtration time was 2 to 3 times that of the gravity type 50 m / day. When the amount of filtration is 4 to 9 times. High pressure (high loss head) filtration generally has been thought that the filtration layer is compressed and suddenly reaches high filtration loss head, and the filtration time does not become as long as expected. The usefulness of became clear.

  Next, it was confirmed that fine sand filtration has a flat turbidity change and no turbidity leakage due to high pressure. In conventional rapid filtration, if a high-loss head is used, water is formed in the filtration layer, and turbidity leaks out. However, in the condition of fine sand and no flocculant, turbidity did not leak out with high loss water head. This is extremely useful data. The present invention could not have been possible if the leakage of turbidity became severe at the time of high loss water head.

  A turbidity of 0.2 to 0.23 degrees is a turbidity removal rate of 80%, which is not good. That is, turbidity removal was incomplete from the beginning to the end of 19 hours under the very special condition of only sieve filtration in the absence of a filtration membrane. From this, it was found that the fine sand used in Example 1 was too large in the filtration of inorganic materials and the like.

  After the experiment in Example 1, the operation was continued with a maximum filtration loss head of 5 m. It is a measurement after 3 weeks after startup. The average turbidity of the raw water was 1 degree. The filtration loss head was 0.7 m at the beginning and 10 m before backwashing, and the pressure was higher than in Example 1. As a result, the filtration time was about 40 hours, which is several times the gravity type, and the average turbidity of filtered water was 0.1 degree. It is estimated that the filtration turbidity was reduced to about half that of Example 1, and the filtration membrane was gradually formed. Further, the filtrate turbidity did not increase at all even when the filtration loss head approached 10 m. It was found that there was no leakage of turbidity even when the filtration loss head was 10 m.

  Using the same plant as in Example 1, measurements were taken after 4 weeks. The filtration loss head was 0.7 to 10 m, the same as in Example 2. The result is shown in FIG. In FIG. 3, the turbidity of the filtered water was as low as 0.08 to 0.11 degrees and was stable although the raw water turbidity was as high as 5 degrees. That is, the turbidity removal rate was about 98%. The high turbidity was due to rain and heavy rivers at night and night, and there was a lot of inorganic turbidity. Therefore, the filtration time is also 8 hours, which is shorter than that of Example 1.

  After startup, it takes about 3 months for the filtration membrane to be completed. In this experiment, the filtration membrane is incomplete because it is 4 weeks later. Nevertheless, filtration is good. It is clear that the turbidity becomes 0.1 degrees or less after 3 months, and the turbidity of 0.1 degrees as a countermeasure against cryptosporidium of tap water can be cleared.

  In the case of Example 2, since the improvement in filtration performance was moderate, there was a concern that it would be difficult to produce a filtration membrane at a filtration rate of 100 m / day, but the result of this Example was worried about the concern. Prove that. That is, it was found that there is no problem with high pressure fine sand filtration even with high speed filtration comparable to rapid filtration. Here is one of the basis of the present invention.

  However, the gradual improvement in filtration performance indicates that the upper limit of the filtration membrane filtration sand is about 0.2 to 0.3 mm. In the slow filtration, the sand particle size is as large as 0.4 to 1 mm because the filtration rate is as small as 4 to 5 m / day.

  It is an important result that high-pressure fine sand filtration does not leak turbidity even in filtration using a filtration membrane. In both the sieve filtration of Example 2 and the filtration membrane filtration of Example 3, turbidity did not leak due to high pressure. This is an important result of the present invention.

  The same plant as in Example 1 was used, and the filtration rate was changed with a slight biofilm of filter sand and a main state of sieve filtration. The raw water was mainly an inorganic turbidity and had a turbidity of 4.5 to 6.9. The filtration water turbidity removal rate was 92% at a filtration rate of 100 m / day, 84% at 200 m / day, 81% at 300 / day, and 80% at 400 m / day. The experiment was started at a filtration loss head of 3 m, but finally increased to 10 m. The turbidity removal rate is higher when the filtration rate is lower, but even when the filtration rate is 400 m / day, the removal rate is still high. Under this high filtration rate condition, it cannot be purified as it is, but it is useful depending on the method of use if it is used as a pretreatment. In order to achieve a turbidity removal rate of about 85 to 95% at a high filtration rate, it is necessary to further reduce the fine sand particle size, but the filtration loss head is increased. In the results of this example, if the relationship between the increase in filtration loss head and the decrease in turbidity removal rate is taken into consideration, approximately 500 m / day is a practical limit.

  When 6.5 cm of fine sand having an effective diameter of 0.075 mm, a uniformity coefficient of 1.42 and an average particle size of 0.10 mm is packed and the inorganic turbid matter is sieve-filtered at a filtration rate of 150 m / day, the filtration loss head is 1.3 m. Met. The filtered water was able to remove 98.9% of turbidity of 2 to 3 μm and 100% of 3 microns or more. According to this data, a sand thickness of 1-2 cm is sufficient to remove 5 μm Cryptosporidium. When the average particle size of the fine sand is 0.03 mm, even if the sand thickness is about 0.2 to 0.3 cm, considering that a supporting fine sand of about 0.1 mm is placed under the sand, sufficient capacity is shown. become.

  Example 5 shows that the fine sand corresponding to the large pore size MF membrane is about 0.1 mm. When fine sand having an effective diameter of 0.02 mm and an average particle diameter of 0.03 mm is used as filtration sand, it is considered to be comparable to the MF membrane itself.

  The sand of Example 5 was backwashed. When the backwash speed was 31 m / day, the expansion rate was 17%, and when the backwash speed was 83 m / day, the expansion rate was 91%. In other words, in the case of fine sand having an average diameter of less than 0.1 mm, it was found that it was difficult to directly filter river surface water with an expansion rate of about 30%. If the separation of turbidity and fine sand of river surface water is complete at 150 m / day or more, the particle size at which the expansion rate is 100% is about 0.12 mm, but the maximum expansion rate is 200%. 0.1 mm is a turning point for whether pretreatment of river surface water is necessary.

  From this experiment, it can be estimated that the expansion rate when the effective diameter is 0.02 mm and the average particle diameter is 0.03 mm is also inversely proportional to the sedimentation speed. Since the sedimentation speed is about 1/10, when the expansion rate is 100%, it becomes about 9 m / day. In the case of this particle size, it can be used as it is for groundwater, but it is indispensable to perform sufficient pretreatment for river surface water.

  25 cm of fine sand having an effective diameter of 0.1 mm, a uniformity coefficient of 1.3, and an average particle diameter of 0.125 mm was packed and subjected to sieving filtration of raw mineral water. The raw water turbidity was 870 degrees, the filtration rate was 100 m / day, and the filtration loss head was increased from 7 m to a maximum of 38 m. The filtered water turbidity was slightly higher, 10 to 12.4 degrees, but was almost constant. The average turbidity is 11.5 degrees and the removal rate is as good as 98.7%. From this, it was revealed that the filtration performance does not deteriorate even when the head loss is higher than that in Example 2.

  Although no higher pressure experiment was conducted, it can be inferred that there is no problem even under the condition of a high-loss head, and that filtration is possible. However, as a practical condition, considering the power cost, it is considered that the filtration loss head is preferably 40 m or less.

It is explanatory drawing of the high pressure type fine sand filter apparatus in embodiment of this invention. It is explanatory drawing of the two-stage high pressure type fine sand filter apparatus in other embodiment of this invention. It is a graph which shows the experimental result based on Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Intake pump 2 Landing tank 3 Raw water pump 4 High pressure type fine sand filtration tank 5 Washing water tank 6 Filtrated water 7 Water collecting device 8 Support gravel layer 9 Support sand layer 10 Filter sand 11 Surface cleaning device 12 Air venting device 13 Cleaning pump 14 Raw water valve 15 Backwash drain valve 16 Surface wash valve 17 Bottom backwash valve 18 Filtration water valve 19 Differential pressure gauge 20 Pre-stage water intake pump 21 Pre-stage water intake tank 22 Pre-stage raw water pump 23 Pre-stage high pressure fine sand filtration tank 24 Pre-stage fine sand filtration Layer 25 Pre-stage surface cleaning device 26 Pre-stage backwash pump 27 Pre-stage water tank

Claims (6)

In a fine sand filtration device that filters raw water such as rivers, lakes, groundwater, and industrial wastewater treatment water, this is a non-flocculating agent high pressure filter, and the effective diameter of fine sand or garnet is 0.02 to 0.2 mm. A pump for supplying the raw water having an average diameter of 0.25 mm or less, filled with 0.2 to 100 cm of filtration sand and having a filtration rate of 30 to 500 m / day, and a backwash rate of 10 to 400 m / day The pressure resistance and pressure detection for efficient filtration by increasing the filtration head loss to 2-40m when filtration is finished and switching to backwash operation. A high-pressure fine sand filtration device comprising an instrument. 2. The high pressure fine sand filtration device according to claim 1, further comprising a surface cleaning pipe for cleaning the fine sand or garnet surface or a grit for loosening the surface to complement backwashing. 3. The high pressure fine sand filtration device according to claim 1, wherein the timing of backwashing is detected by a timer or a filtration loss head and the operation is completely automated. In a fine sand filtration method for filtering raw water such as rivers, lakes, groundwater, and industrial wastewater treatment water, this is a non-flocculating agent high pressure filtration, and 0.2 to 100 cm of fine sand or garnet is filled, and the filtration rate is 30. When equipped with equipment for supplying the raw water of up to 500 m / day and backwash equipment for backwash regeneration with a backwash speed of 10 to 400 m / day, when filtration is completed and switching to backwash operation A high-pressure fine sand filtration method comprising pressure resistance and pressure detection equipment for efficient filtration by increasing the filtration loss head to 2 to 40 m. 5. The high pressure fine sand filtration method according to claim 4, further comprising a mechanism for cleaning the surface of the fine sand or loosening the surface, and supplementing backwashing. The high pressure fine sand filtration method according to claim 4 or 5, wherein the timing of backwashing is detected by a timer or a filtration loss head, and the operation is fully automated.

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