Patent Application
20190046930
The present invention relates to a membrane separation technology in which water to be treated containing impurity is filtrated by using a filtration membrane and a method for manufacturing a filtration membrane.
Regarding water treatments such as a clean water treatment, a sewage treatment, etc., a liquid-solid separation technology, in which a contamination material which is contained in water to be treated is separated from water to be treated so as to obtain clean treated water, has been widely performed. For example, a liquid-solid separation technology includes an aggregation precipitation technology in which an aggregating agent is added to water to be treated so as to make a contamination material which is contained in water to be treated aggregated and precipitated by gravity to be separated, a pressure looming technology in which micro bubble is injected in water to be treated including an aggregated material so as to make an aggregated material absorbed by micro bubble to be loomed and separated. However, regarding the above mentioned technologies, there are problems such that performing treatment is unstable because the above mentioned technologies are extremely susceptible to the property of water to be treated or an aggregated material, a water temperature, water flow, etc., and also a large precipitation water tank and a looming separation tank are necessary.
On the other hand, recently, as an alternative technology, a membrane filtration technology using filtration membrane is widely introduced. According to the above mentioned technology, by using a membrane having an infinite number of holes on a surface, water to be treated is filtrated so as to perform a liquid-solid separation. Membranes are broadly divided into an inorganic membrane which is made of an inorganic material such as ceramic, and an organic membrane which is made of a polymeric organic polymer.
According to the above mentioned technology, when a size of a contamination material in water to be treated is larger than a diameter of a hole of a membrane, a contamination material in water to be treated can be surely separated and eliminated, as a result, extremely clean treated water can be stably obtained. However, there is a problem such that, when filtration treatment is performed, a contamination material is accumulated on a surface of a membrane, a hole of a membrane is slogged with the accumulated contamination material, as a result, performing filtration treatment becomes difficult. Especially, a hydrophobic organic membrane has high affinity with a hydrophobic contamination material which is contained in water to be treated, therefore, a hydrophobic organic membrane is easily slogged. Consequently, it is difficult to stably perform filtration treatment for a long period.
As above mentioned, in a case where a membrane is slogged, it is necessary to recover a filtration ability by performing cleaning using a chemical agent such as an oxidizing agent. Regarding a method of cleaning using a chemical agent, “in line cleaning” in which from a secondary side to a primary side of a membrane, that is, a direction which is opposite to a direction when water to be treated is filtrated, a chemical agent is washed back, is well known. For example, in Patent Document 1, a cleaning method, in which when in line cleaning is performed, at least one of injection concentration of a chemical agent, injection speed of a chemical agent and injection pressure of a chemical agent is varied, is described.
Further, in Patent Document 2, a method of cleaning out strong dirt so as to clean uniformly a membrane by making a differential pressure between inside of a membrane and outside of a membrane when in line cleaning is performed, that is, ‘inter-membrane differential pressure’ a predetermined range according to an inter-membrane differential pressure when a filtration treatment is performed, is described. Further, in a case where a hydrophobic membrane is used for filtrating, by making a membrane to be hydrophilic, filtration performance can be heightened or it is possible to make a membrane not to be slogged. In Patent Document 3, a method for making a membrane to be hydrophilic using ozone of a hydrophobic organic membrane is disclosed. According to a method which is disclosed in Patent Document 3, a hydrophobic organic membrane is soaked in ozone water or ozone water is injected to a membrane which is modularized so as to make ozone water and a membrane contacted, consequently, a hydrophobic organic membrane is made to be hydrophilic.
[Patent Document 1]
JP 2007-61697A
[Patent Document 2]
International publication WO2011-048681A1
[Patent Document 3]
JP 1993-317663A
When a membrane is cleaned or a membrane is made to be hydrophilic, it is important to uniformly contact a membrane and a chemical solution. Inventions which are disclosed by Patent Document 1 and Patent Document 2 aim to decrease unevenness of cleaning when in line cleaning is performed so as to heighten a cleaning effect. However, according to a method which is disclosed by Patent Document 1, for example, when pressure of initial cleaning is not sufficient, a chemical solution does not reach an edge part of a membrane (a part which is the farthest from a point where a chemical solution is injected) and in the vicinity of the part, consequently, a membrane and a chemical solution cannot be contacted sufficiently. On the other hand, in some cases, pressure is given too extremely, as a result, damage of a membrane is generated. Further, even by a method which is disclosed by Patent Document 2, depending on a length or a variety of a membrane to be used, in the same way as the above mentioned, a chemical solution does not reach sufficiently and consequently a membrane and a chemical solution do not contact sufficiently.
Present invention aims to solve the above mentioned problems, and provides a membrane filtration device and a method for cleaning a filtration membrane in which a membrane and a chemical solution for cleaning a membrane or a chemical solution for making a membrane to be hydrophilic can be contacted efficiently.
A membrane filtration device according to present invention has a filtration mode in which by passing water to be treated from a primary side to a secondary side of a filtration membrane, the water to be treated is filtrated, and a filtration membrane cleaning mode in which by passing ozone water from the secondary side to the primary side of the filtration membrane, the filtration membrane is cleaned, and comprises an inter-membrane differential pressure controller which controls an inter-membrane differential pressure ΔP which is a differential between liquid pressure at the primary side of the filtration membrane and liquid pressure at the secondary side of the filtration membrane, and in the filtration membrane cleaning mode, the inter-membrane differential pressure controller controls to gradually decrease the inter-membrane differential pressure ΔP from an initial differential pressure ΔP1 which is sot in advance to a final differential pressure ΔP2 which is a value smaller than a value of the ΔP1.
Further, a filtration membrane cleaning method according to present invention is a filtration membrane cleaning method which has a filtration treatment process in which by passing water to be treated from a primary side to a secondary side of a filtration membrane, the water to be treated is filtrated and subsequently, a filtration membrane cleaning process in which by passing ozone water from the secondary side to the primary side of the filtration membrane, the filtration membrane is cleaned. In the filtration membrane cleaning process, an inter-membrane differential pressure ΔP which is a differential between liquid pressure at the primary side of the filtration membrane and liquid pressure at the secondary side of the filtration membrane is gradually decreased from an initial differential pressure ΔP1 which is set in advance to a final differential pressure ΔP2 which is a value smaller than a value of the ΔP1.
Further, a method for manufacturing a filtration membrane according to present invention is a method for manufacturing a filtration membrane for filtrating liquid by passing the liquid from a primary side to a secondary side, and comprises a filtration membrane hydrophilization process in which by-passing ozone water from the secondary side to the primary side of the filtration membrane so as to hydrophilize the filtration membrane, and in the filtration membrane hydrophilization process, an inter-membrane differential pressure ΔP which is a differential between pressure at the primary side of the filtration membrane and pressure at the secondary side of the filtration membrane is gradually decreased from an initial inter-membrane differential pressure ΔP1 which is set in advance to a final differential pressure ΔP2 which is smaller than a value of ΔP1 so as to pass ozone water.
According to present invention, even when any membrane is used, proper injecting of a chemical solution considering any property of a membrane such as a length or the degree of dirty can be performed, consequently, without damaging a membrane, a membrane and a chemical solution can be contacted uniformly. As a result, an effect of excellent cleaning and an effect of hydrophilic processing can be obtained.
Embodiments of present invention will be described in the following. Embodiments in the following are examples of present invention, and present invention will not be limited to embodiments in the following.
The membrane filtration device 1 shown in
In a filtration mode, the water to be treated 2 is introduced to the water tank 4 via the water to be treated introducing pipe 3. In the water tank 4, activated sludge 5 is stored and an organic contamination material which is contained in the water to be treated 2 is decomposed and removed. The water to be treated 2 which is purged through a predetermined residence time is sucked by the filtrating pump 15 and is filtrated by the filtration membrane 9, and treated water which is obtained is discharged through the treated water transporting pipe 20 to latter stage. In a process of the filtration mode, a differential pressure between a primary side that is a side of un-permeated water and a secondary side, that is a side of permeated water of the filtration membrane 9, that is, an inter-membrane differential pressure is measured by a pressure measuring part 11, that is, a differential pressure gauge 14. The pressure measuring part 11 may be comprised only by a measuring device which can measure an inter-membrane differential pressure as a discrete component such as a differential pressure gauge 14, also the pressure measuring part 11 may have the configuration in which an inter-membrane differential pressure is calculated by using combination of a device which measures only pressure in the treated water transporting pipe 20 and calculating equipment which is provided separately. That is, the pressure measuring part 11 may be equipment or the configuration by which an inter-membrane differential pressure can be measured and is not limited to the configuration shown in
An inter-membrane differential pressure which is measured will be transmitted to the inter-membrane differential pressure controller 13. When an inter-membrane differential pressure which is measured reaches a predetermined value by which cleaning of a filtration membrane is judged to be necessary, a filtration mode will be stopped, a filtration mode will be switched to a filtration membrane cleaning mode in which by an ozone water injection treatment device 12, an ozone water injection treatment is performed from a secondary side to a primary side of the filtration membrane 9. Further, in a filtration mode, a valve 22 is opened and a valve 23 is closed, however, in a filtration membrane cleaning mode, the valve 22 is closed and the valve 23 is opened. In the ozone water injection treatment device 12, ozone gas which is generated by the ozone generator 16 is concentrated by the ozone concentrator 17 so as to be exhausted as ozone gas having high concentration, the ozone gas having high concentration is introduced to the ozone water generator 18 so as to generate ozone water, by the ozone water injecting pump 19, ozone water which is generated is injected to the filtration membrane 9 and the filtration membrane 9 is treated.
Here, as the ozone generator 16, any generator which can generate ozone gas is acceptable, for example, a silent discharge type ozone generator using a glass electrode is taken as an example. Further, by introducing the ozone concentrator 17, ozone gas having higher concentration can be obtained. As the ozone concentrator 17, a concentrator using silica gel as an absorbent may be taken as an example, however, any concentrator having the configuration in which ozone gas can be concentrated and concentrated gas can be taken out freely is acceptable. By providing the ozone concentrator 17, ozone gas having higher concentration can be used, ozone concentration in ozone water which is generated by the ozone water generator 18 can be increased and ozone water injection treatment can be completed in shorter time. However, the ozone concentrator 17 is not necessarily required in present invention.
Regarding the configuration of the ozone water generator 18, the configurations shown in
On the other hand, in
As described in the above, when a chemical solution such as ozone water, etc. is injected from a secondary side to a primary side of a filtration membrane, there is a problem such that a chemical solution and a filtration membrane cannot be contacted uniformly. Especially, inventors of present invention found a problem, that is, according to any existing invention or combination of existing inventions, deficiency and excess of pressure when a chemical solution is injected is generated, a chemical solution can not sufficiently reach an edge part of a filtration membrane or in the vicinity of an edge part, cleaning or hydrophilic treatment cannot be sufficiently performed or a filtration membrane may be damaged. Inventors of present invention grapple with the above mentioned problem earnestly, as a result, the inventors found out such that regarding ozone water injection treatment, by considering the property of membrane and starting injection of a chemical solution with proper pressure and decreasing the pressure to a predetermined injection pressure, a chemical solution can be permeated efficiently to an edge part of a membrane and in the vicinity of an edge part.
That is, in the inter-membrane differential pressure controller 13, an inter-membrane differential pressure, which should be given to a filtration membrane when ozone water injection treatment is performed according to equation (1), is set, and based on the set value, injecting of ozone water is performed by the ozone water injection treatment device 12.
ΔP=f×α×L (1)
Here, ΔP indicates ozone water injecting inter-membrane differential pressure (kPa), f indicates coefficient (m−1), α indicates un-permeability potential (kPa), and L indicates a length of a filtration membrane (m).
ΔP indicates ozone water injecting inter-membrane differential pressure, and indicates an inter-membrane differential pressure which should be given to a filtration membrane when ozone water treatment is performed. f indicates a coefficient. α indicates un-permeability potential and is a value which indicates a degree of permeability of a filtration membrane. That is, α indicates an inter-membrane differential pressure which is detected by the pressure measuring part 11 in membrane filtrating when a filtration mode is terminated just before a filtration mode is switched to a filtration membrane cleaning mode, and is a maximum inter-membrane differential pressure in membrane filtrating. L indicates a length of a filtration membrane. The filtration membrane 9 shown in
In conventional inventions, injection pressure is determined without considering a length of a filtration membrane. According to examination of the inventors of present invention, a length of a filtration membrane is an important factor in determining injection pressure, by injecting a chemical solution with injection pressure which is appropriate to a length of a filtration membrane, a chemical solution can be reliably contacted with whole of a filtration membrane. Pressure loss which is generated by a filtration membrane is in proportion to a length of a filtration membrane, further, it is considered such that the pressure loss is also in proportion to un-permeability potential such as clogging. Consequently, as expressed in equation (1), as a set parameter of inter-membrane differential pressure ΔP which should be generated when ozone water is injected, by introducing a length of a filtration membrane L and a coefficient f, by setting a proper value as a value of a coefficient f, by determining an inter-membrane differential pressure when ozone water is injected, cleaning of a filtration membrane can be effectively performed. Further, regarding a material of a hollow-fiber membrane module and a flat membrane, a material having ozone resistance is preferable, and as a fluorine based organic membrane, polyvinylidene fluoride (PVDF) or poly-tetra-fluoro-ethylene (PTFE) is taken as an example, however, a material is not limited to the above mentioned and any material having ozone resistance and sufficient physical strength which can be resistant to membrane filtration is acceptable.
Further, as a result of the inventors' earnest examination, it is found out such that by injecting ozone water while gradually decreasing a value of ΔP which is obtained by the equation (1) from an initial differential pressure (ΔP1) which is determined in advance to a final differential pressure (ΔP2) when ozone water injection treatment is terminated (ΔP2ΔP1), ozone water can be contacted efficiently, that is, can be contacted uniformly to an end part of a membrane with small amount of ozone water. That is, it is revealed such that it is good for a range of a coefficient f (will be referred as f1, ΔP1=f1×α×L) when P1 is determined to be a range of 0.15≤f1≤1.7, preferably, to be a range of 0.2≤f1≤1.7, and it is good for a range of a coefficient f (will be referred as f2, ΔP2=f2×α×L) when ΔP2 is determined to be a range of 0≤f2≤0.15. However, when ΔP2 is too small, injection pressure will be lacking and injection will be unstable. Further, when ΔP2 is large, a differential between ΔP1 is small, and same effect of present invention can be obtained, however, large pressure with large amount of water has to be kept giving, that is, the above mentioned will be uneconomical. Consequently, it is more preferable to be a range of 0.01≤f2≤0.14, further, it is more preferable to be a range of 0.05≤f2≤0.1, and f1 and f2 will be set individually, and in the above mentioned range, it is good for f1 and f2 to be gradually decreased.
Depending on ozone concentration in ozone water, it is good for ozone water injection time t (minute) to be one minute or longer, preferably, to be a range of 5≤t≤80. Even when ozone water injection time is too long, an effect of present invention will not be lost, however, unnecessary injection is uneconomical. Further, regarding decrease from ΔP1 to ΔP2, while injection time t, it may be linearly decreased or may be exponentially decreased (e−at, a0). According to a method for exponentially decreasing a differential pressure, at first, inside of a filtration membrane will be roughly cleaned, as a result, the ratio of recovery of inter-membrane differential pressure is good. Further, in a case where present invention is performed aiming to clean a membrane, by operating for an inter-membrane differential pressure ΔP to be gradually decreased between an initial differential pressure ΔP1 and a final differential pressure ΔP2, and to repeat increasing or decreasing in a range, which does not exceed ΔP1 as shown with a solid line in
As above mentioned, a flow chart of operation of a membrane filtration device according to Embodiment 1 of present invention will be shown in
As above mentioned, by interlocking the inter-membrane differential pressure controller 13 and the ozone water injection treatment device 12, by injecting ozone water according to a predetermined inter-membrane differential pressure, a filtration membrane can be uniformly contacted with ozone water by using small amount of ozone water, and consequently, cleaning of the filtration membrane 9 can be efficiently completed. Further, when the inter-membrane differential pressure controller 13 has a function for receiving a signal from the pressure measuring part 11 such as PLC or a language controller so as to be able to perform computation of ΔP1 and ΔP2, and based on the calculated result, transmitting a signal to the ozone water injection treatment device 12, based on the above-mentioned logic, performing an ozone water injection treatment, the inter-membrane differential pressure controller 13 can be operated automatically, however, in a case where automatic operation is not necessarily required, when a person who takes charge of operation functions a role of the inter-membrane differential pressure controller 13 and performs an ozone water injection treatment manually according to the above-mentioned logic, an effect of present invention can be obtained.
In Embodiment 2, a process which is same as a filtration membrane cleaning process which is described in Embodiment 1 will be performed as a filtration membrane hydrophilization process in a manufacturing method of a filtration membrane. In a filtration membrane hydrophilization process, in the water tank 4 in which the clean water 50 is stored, a filtration membrane 9 to be manufactured, that is, the filtration membrane 9 which is an objective of hydrophilization will be set, and by an ozone water injection treatment device 12, ozone water is passed from a secondary side to a primary side of the filtration membrane 9.
Regarding the way of decreasing an inter-membrane differential pressure ΔP gradually from ΔP1 to ΔP2, as described in Embodiment 1, it may be linearly decreased or may be exponentially decreased. Further, as shown in
As described in Embodiment 1, at this time, in a case where un-permeability potential of a filtration membrane is α, a length of a filtration membrane is L when a filtration membrane hydrophilization process starts, by introducing a coefficient f, an inter-membrane differential pressure ΔP may be determined by α×L×f.
When a coefficient f for determining an initial membrane differential ΔP1 is set to be f1 and a coefficient f for determining a final membrane differential pressure is set to be f2, f1may be 0.15 or larger, or less than 1.7, and f2 may be 0 or larger, or less than 0.15.
Further, in this case, it is not always necessary to measure un-permeability potential α of all filtration membranes. That is, in a case where quality is stable at a manufacturing stage, it is sufficient to measure un-permeability potential α of at least one filtration membrane per each lot, and regarding other filtration membrane module which constitutes a lot, by using a value of the same α, a filtration membrane hydrophilization process may be performed.
As above mentioned, in Embodiment 2, present invention is applied to a filtration membrane hydrophilization process in a manufacturing method of a filtration membrane, ozone water uniformly can be contacted to an end part of a membrane with small amount of ozone water, as a result, a method for efficiently manufacturing a filtration membrane can be provided.
Hereinafter, in a filtration membrane device which is described in Embodiment 1, an example in which after water to be treated is filtrated, cleaning of a filtration membrane is performed by ozone water injection treatment which is based on present invention, and a comparative example in which cleaning of a filtration membrane is performed by ozone water injection treatment which is not based on present invention will be described.
By using a membrane having a length of 1.2 m of module L, according to a membrane separation activated sludge method having the configuration which is same as that shown in
Recovery Ratio of Differential Pressure (%)=[1−{(Pa−Pb)/30}]×100 (2)
A length of cleaning time is fixed to be 30 minutes and a value of f2 is fixed to be 0.14. Further, a cleaning treatment is performed automatically by an inter-membrane differential pressure controller for 30 minutes so as for an inter-membrane differential pressure ΔP to decrease linearly from ΔP1 to ΔP2. α is 30 kPa. Obtained result will be shown in
By using a membrane having a length of 1.2 m of module L, according to a membrane separation activated sludge method having the configuration which is same as that shown in
Obtained result will be shown in
By using a membrane having a length of 1.2 m of module L, according to a membrane separation activated sludge method having the configuration which is same as that shown in
Obtained result will be shown in
By using a membrane having a length of 1.2 m of module L, according to a membrane separation activated sludge method having the configuration which is same as that shown in
Under the condition which is same as that of Embodiment 4, an inter-membrane differential pressure in cleaning is exponentially decreased from ΔP1 to ΔP2, for 30 minutes.
Under the condition which is same as that of Embodiment 4, from ΔP1 to ΔP2, in a range which does not exceed ΔP1, so as for ΔP to be a maximal value or a minimal value alternatively, every four minutes, an inter-membrane differential pressure ΔP is decreased step by step by repeating increase and decrease.
By using a membrane having a length of 1.2 m of module L, by setting an inter-membrane differential pressure α to be 30 kPa, by setting the upper limit of an inter-membrane differential pressure in cleaning to be 5 kPa, by setting the lower limit of an inter-membrane differential pressure in cleaning to be 3.6 kPa, by setting a length of cleaning time to be 30 minutes, and by setting ozone water concentration to be 50 mg/L, a cleaning process using ozone water is performed by using alternately the upper limit of pressure and the lower limit of pressure in cleaning every 4 minutes.
By using a membrane having a length of 1.2 m, of module L, by setting an inter-membrane differential pressure α to be 30 kPa, by setting ozone water concentration to be 50 mg/L, while a differential pressure is maintained to be 95 kPa, a cleaning process is performed using ozone water.
By using a membrane having a length of 1.2 m of module L, by setting an inter-membrane differential pressure α to be 30 k Pa, by setting ozone water concentration to be 50 mg/L, while a differential pressure is maintained to be 19 kPa, a cleaning process is performed using ozone water.
By using a membrane having a length of 1.2 m of module L, by setting an inter-membrane differential pressure α to be 30 kPa, by setting the upper limit of an inter-membrane differential pressure in cleaning to be 19 kPa by setting the lower limit of an inter-membrane differential pressure in cleaning to be 7.2 kPa, by setting a length of cleaning time to be 30 minutes, and by setting ozone water concentration to be 50 mg/L, a cleaning process using ozone water is performed by using alternately the upper limit of pressure and the lower limit of pressure in cleaning, every 4 minutes.
Transition of an inter-membrane differential pressure in cleaning with ozone water in Examples 4 to 6 and Comparative Examples 1 to 4 will be shown in
Results of Examples 4 to 6 and Comparative Examples 1 to 4 will be shown in Table 1. In Examples 4 to 6 to which present invention is applied, high recovery ratio of an inter-membrane differential pressure can be obtained. Especially, according to a cleaning method of Example 6, the highest recovery ratio of an inter-membrane differential pressure is obtained. On the other hand, in Comparative Examples 1 to 4, a membrane is damaged, recovery ratio of an inter-membrane differential pressure is low, and an amount of ozone injection is large, that is, the operation is not effective.
By considering a length of a membrane and by maintaining a value of f1 and f2 to be a proper range, by adding proper pressure and by passing ozone water from a secondary side to a primary side of a filtration membrane, excellent cleaning effect can be obtained. As above mentioned, it is clear such that present invention is superior to conventional inventions.
Further, it is understood such that in present invention, combination of each embodiment proper arrangement or omitting may be resorted to without departing from the spirit and scope thereof.
1. membrane filtration device
2. water to be treated
9. filtration membrane
12. ozone water injection treatment device
13. inter-membrane differential pressure controller
17. ozone concentrator
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/056796 | 3/4/2016 | WO | 00 |
