WO1995014524A1 - Improved membrane type liquid purification system - Google Patents

Improved membrane type liquid purification system Download PDF

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Publication number
WO1995014524A1
WO1995014524A1 PCT/IB1994/000429 IB9400429W WO9514524A1 WO 1995014524 A1 WO1995014524 A1 WO 1995014524A1 IB 9400429 W IB9400429 W IB 9400429W WO 9514524 A1 WO9514524 A1 WO 9514524A1
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WO
WIPO (PCT)
Prior art keywords
liquid
purified
membrane
unit
purification system
Prior art date
Application number
PCT/IB1994/000429
Other languages
French (fr)
Inventor
Mike Myers
Original Assignee
Pure Pac Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Pure Pac Inc. filed Critical Pure Pac Inc.
Priority to AU11174/95A priority Critical patent/AU1117495A/en
Publication of WO1995014524A1 publication Critical patent/WO1995014524A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/025—Reverse osmosis; Hyperfiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/08—Apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
    • B01D65/02—Membrane cleaning or sterilisation ; Membrane regeneration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
    • B01D2321/02—Forward flushing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
    • B01D2321/04—Backflushing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
    • B01D2321/16—Use of chemical agents

Definitions

  • the invention relates to an improved membrane type liquid purification system, more particularly to a system using reverse osmosis.
  • the invention can be used primarily for purifying water of a lower level of purity.
  • Membrane type liquid purification is well known in the art and very high degree of purification can be reached if the purification utilizes reverse osmosis. This latter technique often requires a sufficient extent of prepuri- fication. Water purification constitutes the most dominant field of liquid purification, therefore in the following part of the description primarily this technique will be mentioned, although similar considerations may be applied in case of purifying other types of liquids.
  • the purified water will have a lower pH and will be well below the solubility limit of the contaminates that are contained in the feed water.
  • a major contaminate found in most feed water that causes a scaling problem is calcium carbonate.
  • the solubility product is a constant that indicates the total solubility of a given substance in water. Exceeding this limit will produce a scale that may be deposited on the membrane surface. This scaling will decrease the flux rate of the membrane (i.e. the amount of purified water that will pass through the membrane) and thereby require that the membrane be cleaned more frequently to remove the scale. In fact, if the scaling becomes too severe, the membrane will be irreversibly fouled and will need to be replaced.
  • Scale preventing or decreasing pretreatment methods are widely applied which include mainly softening. Salts used for softening the feedwater provide a salt loading to theen- vironment and increase operational costs. Apart from directly decreasing the flux rate through the membrane, scaling has further adverse side effects. As the amount of scale increases during use, more sites for biolo ⁇ gical growth will be available both in the membrane and in the associated piping. Biological growth has at least two negative impacts on the effectivity of membrane performance. First, the biological growth contaminates the feed side of the membrane with bacteria, viruses and the like which have the potential to migrate to the water on the purified side of the membrane thus contaminating the product water. Se ⁇ condly, the biological growth itself can foul the membrane thus reducing the flux rate.
  • German patent 3.106.772 a reverse osmosis water puri ⁇ fication method is described, in which an adjustable portion of the permeate leaving the membrane module is recycled to the atmospheric tank that contains the feed raw water.
  • the method is capable of providing a more uniform composition of the feed water by diluting the same in case of higher degree of contamination.
  • recycled water together with feed water is passed through the membrane under operational pressure conditions.
  • the primary object of the invention is to provide a mem ⁇ brane-based purification system and purification method, in which scaling is effectively reduced compared to conven ⁇ tional systems of comparable output.
  • a further object of the invention is to reduce environ ⁇ mental load by decreasing or eliminating the need of soften ⁇ ing the feed water.
  • a still further object of the invention is to provide a purification system and method with decreased tendency of biological growth.
  • puri ⁇ fied liquid can be reintroduced to the system in cleaning cycles instead of non-purified feed liquid so that this liquid can contact the input side of the semi permeable membrane, whereby contaminates present in the system, mainly those deposited on the membrane, can go into solution due to the lower solubility product and lower pH of the purified liquid and the redissolved contaminates can be removed to ⁇ gether with the reintroduced liquid.
  • the cleaning or re ⁇ versing of the scaling on the membrane surface is due to the increased ability of the purified liquid (e.g. water) to re- dissolve the minerals that caused the scaling due to the fact that the liquid would not be saturated with, and there ⁇ by not in equilibrum with, a given contaminant.
  • a membrane type liquid purification system which comprises:
  • -a supply means feeding a liquid to be purified
  • -a purification unit with a membrane and having an inflow port connectable to the supply means and an outflow port delivering purified liquid, the liquid to be purified is separated by the membrane from the purified liquid;
  • -pump means for passing liquid through the membrane with a predetermined first pressure in purifying cycles when the supply means is connected to the inflow port and refeeding purified liquid with a predetermined second pressure to the inflow port in cleaning cycles when the port is coupled to the redistribution loop;
  • -discharge means for discharging at least a portion of the resupplied purified liquid together with any contami ⁇ nants redissolved from the membrane during the cleaning cycles.
  • the purification unit is a reverse osmosis unit which has a reject liquid port and the dis ⁇ charge means is connected to the reject liquid port.
  • the discharge means comprises a tube with a portion having a smaller cross section and the tube has a free end connectable to a drain.
  • valve means comprises a control unit supplying switching signals in response to predeter ⁇ mined first and second liquid levels in the storage means, a feed valve connected between the supply means and the inflow port controlled by the switching signal, and the pump means comprises a first pump connected between the feed valve and the inflow port, the first pump is activated in the purify ⁇ ing cycles by the control unit and provides the first pres ⁇ sure, and wherein the second pressure is lower than the first pressure.
  • the pump means may further comprise a second pump pro ⁇ viding recirculation in the redistribution loop.
  • pressure decreasing means and biased valve means are connected in the path between the redistribution loop and the inflow port to pro ⁇ vide the second pressure during the cleaning cycles and to prevent flow of liquid to the redistribution loop from the supply means during the cleaning cycles.
  • the system may further comprise pressure regulating means keeping pressure in the redistribution loop within predetermined limit values.
  • a valve can be used for preventing reverse flow of li ⁇ quid between the unit and the storage means.
  • the liquid to be purified is water.
  • a method for purifying a liquid by a mer.brane type purify ⁇ ing unit which comprises the steps of:
  • interruption periods resupplying previously purified liquid towards the unit to get into contact with inflow side of the membrane and to dissolve any soluble contaminants that might have previously been deposited on the inflow side of the membrane;
  • the passage of the liquid to be purified is applied with a pressure that exceeds the one applied during the resupplying step.
  • the purifying unit is preferably a reverse osmosis unit and the discharging step relates to the liquid rejected by said membrane.
  • the main advantage of the invention lies in the in ⁇ creased lifetime of the membrane due to the decreased extent of scaling which reduces operational and investment costs and increases reliability.
  • An associated advantage lies in that there might be no need for specific scale preventing pretreatment of the feed water such as softening and this reduces material consumption and environmental load caused by the discharge of salt as well as costs.
  • the biological growth will also be minimized due to both the lack of sites for the biological growth to attach to and in the case of the fluid flowing past the membrane to drain in the cleaning cycles, the bacteria, etc. are continuously removed from the system thereby adding to the sanitary nature of the purified water.
  • Fig. 1 shows the schematic layout of a preferred embodi ⁇ ment of the liquid purifying system according to the invention.
  • the simplified reverse osmosis membrane type purifica ⁇ tion system shown in Fig. 1 comprises a pretreatment line for the unpurified water entering in the system which con ⁇ sists of a carbon filter 1 and a prefilter 2.
  • Feed valve 3 is connected in the outflow line of the prefilter 2 cont ⁇ rolled by control unit 20 in response to water level in sto ⁇ rage tank 9.
  • the outflow line of the feed valve 3 is connected to pressurizing pump 4 feeding input of a reverse osmosis unit comprising a semi permeable membrane 6.
  • a first check valve 5 is connected in parallel with the pressurizing pump 4 and it has a bias pressure smaller than the pressure provided by the pressurizing pump 4 so that the first check valve 5 is closed when the pressurizing pump 4 is running.
  • a second check valve 15 is connected to the junction of the feed valve 3 and the input of the pressurizing pump 4.
  • a the se ⁇ cond check valve 15 has a smaller bias pressure than the first one and it is kept closed by the operational pressure of the feed water if the feed valve 3 is in open condition.
  • Reject fluid outflow line of the reverse osmosis unit has a restriction orifice 7 defining a flow path with re ⁇ quizd cross section.
  • the outflow opening of this line leads to a vented drain 8.
  • the reverse osmosis unit has a purified water outflow line leading through a third check valve 16 to the inlet of the storage tank 9.
  • the third check valve 16 has the task of prohibiting any reverse flow of water from the storage tank 9 to the reverse osmosis unit that would otherwise jeopardize correct operation of the membrane 6.
  • Outflow line of the storage tank 9 is connected directly or through optional deionization and ultraviolet steriliza ⁇ tion units (not shown) to repressurization pump 10 providing pressure and sufficient flow to a distribution loop 11 feed ⁇ ing outflow lines 12 connectable to end users of the puri ⁇ fied water.
  • a feedback line of the distribution loop 11 is " ⁇ O ⁇
  • the feed water is supplied through the pretreatment line at a predetermined pressure e.g. 50 psi to the input of the purification system.
  • the purity of the supplied water should fall in the operational input range of the reverse osmosis unit. If the water level in the storage tank 9 is below a predetermined maximum value, the control unit 20 opens the path of the feed valve 3 and makes the pressurizing pump 4 running. The input pressure of about 50 psi closes the second check valve 15.
  • the pressurizing pump 4 boosts the feed water pressure to a higher value e.g. to 200 psi and this pressure prevails at the semi permeable membrane 6. Purified water will pass through the membrane 6 due to the fact that the selected input pressure overcomes the osmotic pressure that would otherwise prevail between the two sides of the membrane 6. This pressure keeps the first check valve 5 closed and the purified water leaving the reverse osmosis units flows through the now open third check valve 16 in the storage tank 9.
  • the reject water that comprises the concentrated impuri ⁇ ties will flow through the restriction orifice 7 and reach the vented drain 8.
  • the repressurization pump 10 provides an output pressure in the outflow line of the storage tank 9 required in the redistribution loop.
  • the pressure regulating valve ensures that this pressure remains below a predetermined maximum value.
  • the consumers connected to the system through the outflow lines 12 will always receive purified water.
  • the control unit 20 turns over, closes the feed valve 3 and stops the pres- surizing pump 4.
  • the pressure at the input side of the reverse osmosis unit decreases, since the reject line is coupled through the restriction orifice 7 to an open end.
  • purified water will flow from the distribution loop 11 through the second restriction orifice 14 to the input side of the reverse osmosis unit.
  • This flow streams to the reject line of the reverse osmosis unit passes through the first restriction orifice 7 and leaves the system at the vented drain 8.
  • the flow rate can be adjusted by the appropriate selection of the cross sec ⁇ tion of the two restriction orifices 7 and 14 and of the connecting pipes.
  • the purified water in the distribution loop 11 contains substantially less amount of contaminants than the original feed water, therefore the solubility product of the conta ⁇ minants (e.g. calcium and carbonate ions) deposited on the input side of the membrane 6 will be lower than in case of feed water. This results in that the contaminants previously deposited or precipitated on the membrane 6 will go into solution and they will be removed with the reject water. This action is further enhanced due to the lower pH of the purified water which increases solubility.
  • the bias pressure of the third check valve 16 prevents the flow of purified water towards the storage tank 20 during the cleaning cycles.
  • the control unit 20 has a certain extent of hysteresis so that the cleaning cycle does not end in the moment when the water level in the tank starts decreasing. With approp ⁇ riate dimensioning it can be provided that a major portion of soluble contaminants will be removed from the membrane 6 which dramatically increases the useful life reverse osmosis system.
  • the cleaning cycle is connected with a given loss of purified water but in exchange of this loss an increased lifetime is obtained during which much more amount of puri ⁇ fied water can be produced.
  • the control unit 20 turns over again and the next purification cycle is started which utilizes now a sufficiently cleaned membrane 6.
  • the invention can in no way be limited to the preferred embodiment shown by way of example only.
  • the storage tank 9 can be replaced e.g. by a bladder tank and the required flow can be provided by other layout of the tubes and pumps as well.

Abstract

A membrane type liquid purification system that comprises: a supply means feeding a liquid to be purified; a purification unit with a membrane (6) and having an inflow port connectable to the supply means and an outflow port delivering purified liquid, the liquid to be purified is separated by the membrane (6) from the purified liquid; a purified liquid storage means (9) connected to the outflow port for storing the purified liquid; a redistribution loop coupled to the storage means (9) for supplying users of the system with purified liquid; a valve means for alternatively connecting the inflow port with the supply means and the redistribution loop; pump means (4) for passing liquid through the membrane (6) with a predetermined first pressure in purifying cycles when the supply means is connected to the inflow port and refeeding purified liquid with a predetermined second pressure to the inflow port in cleaning cycles when the port is coupled to the redistribution loop; and discharge means for discharging at least a portion of the resupplied purified liquid together with any contaminants redissolved from the membrane during the cleaning cycles.

Description

IMPROVED MEMBRANE TYPE LIQUID PURIFICATION SYSTEM
The invention relates to an improved membrane type liquid purification system, more particularly to a system using reverse osmosis. The invention can be used primarily for purifying water of a lower level of purity.
Membrane type liquid purification is well known in the art and very high degree of purification can be reached if the purification utilizes reverse osmosis. This latter technique often requires a sufficient extent of prepuri- fication. Water purification constitutes the most dominant field of liquid purification, therefore in the following part of the description primarily this technique will be mentioned, although similar considerations may be applied in case of purifying other types of liquids.
The nature of membrane-based separation technologies, by and large, rely on rejecting a portion of the feedwater during the 'production* of the purified fluid. During the purification of water the rejection of a portion of the feed water stream allows the removal of the concentrated conta¬ minates on the 'concentrate' side of the membrane and the rejected stream is diverted to a drain or re-used in non- critical applications. The amount of the contaminates that are rejected is a function of the membrane, the feed water composition, the system design and operating conditions. The water that passes through a reverse osmosis membrane, for example, typically has 98% of the contaminants found in the feed water removed. Once the water has passed through the membrane, the purified water will have a lower pH and will be well below the solubility limit of the contaminates that are contained in the feed water. For example, a major contaminate found in most feed water that causes a scaling problem is calcium carbonate. As the calcium ion and carbon¬ ate ion are concentrated due to the nature of membrane-based systems, the possibility exists to exceed the solubility product of the calcium carbonate in the feed water. The solubility product is a constant that indicates the total solubility of a given substance in water. Exceeding this limit will produce a scale that may be deposited on the membrane surface. This scaling will decrease the flux rate of the membrane (i.e. the amount of purified water that will pass through the membrane) and thereby require that the membrane be cleaned more frequently to remove the scale. In fact, if the scaling becomes too severe, the membrane will be irreversibly fouled and will need to be replaced.
The higher the recovery, i.e. the ratio of the volume of the purified water divided by the feed water consumed, the lower is the demand on the source of the water and the lower is the capital cost of the equipment per unit volume of wa¬ ter that is purified. A trade off exists, however, between the recovery of the system and the ability of the membranes to continue to function for extended periods of time without the need for cleaning or from being irreversibly fouled by the contaminants in the unpurified feed water by the pre¬ viously mentioned scaling problem.
It has been experienced in reverse osmosis type memb¬ ranes that a portion of the contaminates in the feed water will not be rejected but be deposited on the membrane sur¬ face. These type of compounds include among other ones, calcium carbonate, barium sulfate and the like. The scaling potential is a term that expresses this tendency and it is a major design limitation in any system that uses membrane- based separation technique due to the potential loss of flux rate with time.
Scale preventing or decreasing pretreatment methods are widely applied which include mainly softening. Salts used for softening the feedwater provide a salt loading to theen- vironment and increase operational costs. Apart from directly decreasing the flux rate through the membrane, scaling has further adverse side effects. As the amount of scale increases during use, more sites for biolo¬ gical growth will be available both in the membrane and in the associated piping. Biological growth has at least two negative impacts on the effectivity of membrane performance. First, the biological growth contaminates the feed side of the membrane with bacteria, viruses and the like which have the potential to migrate to the water on the purified side of the membrane thus contaminating the product water. Se¬ condly, the biological growth itself can foul the membrane thus reducing the flux rate.
In German patent 3.106.772 a reverse osmosis water puri¬ fication method is described, in which an adjustable portion of the permeate leaving the membrane module is recycled to the atmospheric tank that contains the feed raw water. The method is capable of providing a more uniform composition of the feed water by diluting the same in case of higher degree of contamination. In this method recycled water together with feed water is passed through the membrane under operational pressure conditions.
The primary object of the invention is to provide a mem¬ brane-based purification system and purification method, in which scaling is effectively reduced compared to conven¬ tional systems of comparable output.
A further object of the invention is to reduce environ¬ mental load by decreasing or eliminating the need of soften¬ ing the feed water.
A still further object of the invention is to provide a purification system and method with decreased tendency of biological growth.
It has been found according to the invention that puri¬ fied liquid can be reintroduced to the system in cleaning cycles instead of non-purified feed liquid so that this liquid can contact the input side of the semi permeable membrane, whereby contaminates present in the system, mainly those deposited on the membrane, can go into solution due to the lower solubility product and lower pH of the purified liquid and the redissolved contaminates can be removed to¬ gether with the reintroduced liquid. The cleaning or re¬ versing of the scaling on the membrane surface is due to the increased ability of the purified liquid (e.g. water) to re- dissolve the minerals that caused the scaling due to the fact that the liquid would not be saturated with, and there¬ by not in equilibrum with, a given contaminant.
A membrane type liquid purification system has thus been provided which comprises:
-a supply means feeding a liquid to be purified;
-a purification unit with a membrane and having an inflow port connectable to the supply means and an outflow port delivering purified liquid, the liquid to be purified is separated by the membrane from the purified liquid;
-a purified liquid storage means connected to the out¬ flow port for storing the purified liquid;
-a redistribution loop coupled to the storage means for supplying users of the system with purified liquid;
-a valve means for alternatively connecting the inflow port with the supply means and the redistribution loop;
-pump means for passing liquid through the membrane with a predetermined first pressure in purifying cycles when the supply means is connected to the inflow port and refeeding purified liquid with a predetermined second pressure to the inflow port in cleaning cycles when the port is coupled to the redistribution loop; and
-discharge means for discharging at least a portion of the resupplied purified liquid together with any contami¬ nants redissolved from the membrane during the cleaning cycles.
It is preferable if the purification unit is a reverse osmosis unit which has a reject liquid port and the dis¬ charge means is connected to the reject liquid port.
In a preferable embodiment the discharge means comprises a tube with a portion having a smaller cross section and the tube has a free end connectable to a drain.
It is preferable if the valve means comprises a control unit supplying switching signals in response to predeter¬ mined first and second liquid levels in the storage means, a feed valve connected between the supply means and the inflow port controlled by the switching signal, and the pump means comprises a first pump connected between the feed valve and the inflow port, the first pump is activated in the purify¬ ing cycles by the control unit and provides the first pres¬ sure, and wherein the second pressure is lower than the first pressure.
The pump means may further comprise a second pump pro¬ viding recirculation in the redistribution loop.
In a preferable further embodiment pressure decreasing means and biased valve means are connected in the path between the redistribution loop and the inflow port to pro¬ vide the second pressure during the cleaning cycles and to prevent flow of liquid to the redistribution loop from the supply means during the cleaning cycles.
The system may further comprise pressure regulating means keeping pressure in the redistribution loop within predetermined limit values.
A valve can be used for preventing reverse flow of li¬ quid between the unit and the storage means.
In most cases the liquid to be purified is water.
A method has also been provided according to the invention for purifying a liquid by a mer.brane type purify¬ ing unit which comprises the steps of:
-passing the liquid to be purified towards the purifying unit;
-passing at least a portion of the liquid through the membrane in the unit to provide a purified liquid;
-collecting the purified liquid in a storage tank, wherein the improvement lies in the steps of:
-periodically interrupting the passage of the liquid to be purified towards the purifying unit;
-during the interruption periods resupplying previously purified liquid towards the unit to get into contact with inflow side of the membrane and to dissolve any soluble contaminants that might have previously been deposited on the inflow side of the membrane; and
-discharging the resupplied liquid together with the dissolved contaminants.
It is preferable if the passage of the liquid to be purified is applied with a pressure that exceeds the one applied during the resupplying step.
The purifying unit is preferably a reverse osmosis unit and the discharging step relates to the liquid rejected by said membrane.
The main advantage of the invention lies in the in¬ creased lifetime of the membrane due to the decreased extent of scaling which reduces operational and investment costs and increases reliability. An associated advantage lies in that there might be no need for specific scale preventing pretreatment of the feed water such as softening and this reduces material consumption and environmental load caused by the discharge of salt as well as costs.
By ensuring that the scale is kept to a minimum, the biological growth will also be minimized due to both the lack of sites for the biological growth to attach to and in the case of the fluid flowing past the membrane to drain in the cleaning cycles, the bacteria, etc. are continuously removed from the system thereby adding to the sanitary nature of the purified water.
The invention will now be described in connection with a preferable embodiment thereof, in which reference will be made to the accompanying drawing. In the drawing:
Fig. 1 shows the schematic layout of a preferred embodi¬ ment of the liquid purifying system according to the invention.
The simplified reverse osmosis membrane type purifica¬ tion system shown in Fig. 1 comprises a pretreatment line for the unpurified water entering in the system which con¬ sists of a carbon filter 1 and a prefilter 2. Feed valve 3 is connected in the outflow line of the prefilter 2 cont¬ rolled by control unit 20 in response to water level in sto¬ rage tank 9.
The outflow line of the feed valve 3 is connected to pressurizing pump 4 feeding input of a reverse osmosis unit comprising a semi permeable membrane 6. A first check valve 5 is connected in parallel with the pressurizing pump 4 and it has a bias pressure smaller than the pressure provided by the pressurizing pump 4 so that the first check valve 5 is closed when the pressurizing pump 4 is running. A second check valve 15 is connected to the junction of the feed valve 3 and the input of the pressurizing pump 4. A the se¬ cond check valve 15 has a smaller bias pressure than the first one and it is kept closed by the operational pressure of the feed water if the feed valve 3 is in open condition.
Reject fluid outflow line of the reverse osmosis unit has a restriction orifice 7 defining a flow path with re¬ duced cross section. The outflow opening of this line leads to a vented drain 8. The reverse osmosis unit has a purified water outflow line leading through a third check valve 16 to the inlet of the storage tank 9. The third check valve 16 has the task of prohibiting any reverse flow of water from the storage tank 9 to the reverse osmosis unit that would otherwise jeopardize correct operation of the membrane 6.
Outflow line of the storage tank 9 is connected directly or through optional deionization and ultraviolet steriliza¬ tion units (not shown) to repressurization pump 10 providing pressure and sufficient flow to a distribution loop 11 feed¬ ing outflow lines 12 connectable to end users of the puri¬ fied water. A feedback line of the distribution loop 11 is "~ O ~
connected both to a pressure regulating valve 13 leading back to the storage tank 9 and to a second restriction ori¬ fice 14 connected to the second check valve 15.
The operation of this water purification system is as follows:
The feed water is supplied through the pretreatment line at a predetermined pressure e.g. 50 psi to the input of the purification system. The purity of the supplied water should fall in the operational input range of the reverse osmosis unit. If the water level in the storage tank 9 is below a predetermined maximum value, the control unit 20 opens the path of the feed valve 3 and makes the pressurizing pump 4 running. The input pressure of about 50 psi closes the second check valve 15.
The pressurizing pump 4 boosts the feed water pressure to a higher value e.g. to 200 psi and this pressure prevails at the semi permeable membrane 6. Purified water will pass through the membrane 6 due to the fact that the selected input pressure overcomes the osmotic pressure that would otherwise prevail between the two sides of the membrane 6. This pressure keeps the first check valve 5 closed and the purified water leaving the reverse osmosis units flows through the now open third check valve 16 in the storage tank 9.
The reject water that comprises the concentrated impuri¬ ties will flow through the restriction orifice 7 and reach the vented drain 8.
The repressurization pump 10 provides an output pressure in the outflow line of the storage tank 9 required in the redistribution loop. The pressure regulating valve ensures that this pressure remains below a predetermined maximum value. The consumers connected to the system through the outflow lines 12 will always receive purified water.
When the storage tank 9 has been filled i.e. the water level has reached the preset maximum value, the control unit 20 turns over, closes the feed valve 3 and stops the pres- surizing pump 4. The pressure at the input side of the reverse osmosis unit decreases, since the reject line is coupled through the restriction orifice 7 to an open end. When the pressure drops below the level of the first and second check valves 15 and 5, purified water will flow from the distribution loop 11 through the second restriction orifice 14 to the input side of the reverse osmosis unit. This flow streams to the reject line of the reverse osmosis unit, passes through the first restriction orifice 7 and leaves the system at the vented drain 8. The flow rate can be adjusted by the appropriate selection of the cross sec¬ tion of the two restriction orifices 7 and 14 and of the connecting pipes.
The purified water in the distribution loop 11 contains substantially less amount of contaminants than the original feed water, therefore the solubility product of the conta¬ minants (e.g. calcium and carbonate ions) deposited on the input side of the membrane 6 will be lower than in case of feed water. This results in that the contaminants previously deposited or precipitated on the membrane 6 will go into solution and they will be removed with the reject water. This action is further enhanced due to the lower pH of the purified water which increases solubility. The bias pressure of the third check valve 16 prevents the flow of purified water towards the storage tank 20 during the cleaning cycles.
The control unit 20 has a certain extent of hysteresis so that the cleaning cycle does not end in the moment when the water level in the tank starts decreasing. With approp¬ riate dimensioning it can be provided that a major portion of soluble contaminants will be removed from the membrane 6 which dramatically increases the useful life reverse osmosis system. The cleaning cycle is connected with a given loss of purified water but in exchange of this loss an increased lifetime is obtained during which much more amount of puri¬ fied water can be produced. When the water level in the storage tank 9 decreases below a threshold level, the control unit 20 turns over again and the next purification cycle is started which utilizes now a sufficiently cleaned membrane 6.
The invention can in no way be limited to the preferred embodiment shown by way of example only. The storage tank 9 can be replaced e.g. by a bladder tank and the required flow can be provided by other layout of the tubes and pumps as well.
While the best results can be reached with a reverse osmosis type water purification unit, the removal of con¬ taminants deposited on the input side of the membrane will take place also if an other membrane type purification unit is used.

Claims

Claims :
1. A membrane type liquid purification system compris¬ ing:
-a supply means feeding a liquid to be purified;
-a purification unit comprising a membrane, said unit has an inflow port connectable to said supply means and an outflow port delivering purified liquid, the liquid to be purified being separated by said membrane from said purified liquid;
-a purified liquid storage means connected to said out¬ flow port for storing said purified liquid;
-a redistribution loop coupled to said storage means for supplying users of said system with purified liquid;
-a valve means for alternatively connecting said inflow port with said supply means and said redistribution loop;
-pump means for passing liquid through said membrane with a predetermined first pressure in purifying cycles when said supply means is connected to said inflow port and refeeding purified liquid with a predetermined second pres¬ sure to said inflow port in cleaning cycles when said port is coupled to said redistribution loop; and
-discharge means for discharging at least a portion of said refed purified liquid together with any contaminants redissolved from said membrane during said cleaning cycles.
2. The liquid purification system as claimed in claim 1, wherein said purification unit is a reverse osmosis unit comprising a reject liquid port.
3. The liquid purification system as claimed in claim 2, wherein said discharge means is connected to said reject liquid port.
4. The liquid purification system as claimed in claim 3, wherein said discharge means comprises a tube with a portion having a smaller cross section and said tube has a free end connectable to a drain.
5. The liquid purification system as claimed in claim 1, wherein said valve means comprising a control unit supplying switching signals in response to predetermined first and second liquid levels in said storage means, a feed valve connected between said supply means and said inflow port controlled by said switching signal, and said pump means comprises a first pump connected between said feed valve and said inflow port, said first pump being activated in said purifying cycles by said control unit and provides said first pressure, and wherein said second pressure being lower than said first pressure.
6. The liquid purification system as claimed in claim 5, wherein said pump means further comprises a second pump providing recirculation in said redistribution loop.
7. The liquid purification system as claimed in claim 6, wherein pressure decreasing means and biased valve means being connected in the path between the redistribution loop and the inflow port to provide said second pressure during said cleaning cycles and to prevent flow of liquid to said redistribution loop from said supply means during said cleaning cycles.
8. The liquid purification system as claimed in claim 1, further comprising pressure regulating means keeping pres¬ sure in said redistribution loop within predetermined limit values.
9. The liquid purification system as claimed in claim 1, comprising means for preventing reverse flow of liquid bet¬ ween said unit and said storage means.
10. The liquid purification system as claimed in claim 1, wherein said liquid is water.
11. In a method for purifying a liquid by a membrane type purifying unit which comprises the steps of:
-passing the liquid to be purified towards said unit;
-passing at least a portion of the liquid through the membrane in the unit to provide a purified liquid;
-collecting said purified liquid in a storage tank, the improvement lies in the steps of:
-periodically interrupting the passage of said liquid to be purified towards said unit;
-during the interruption periods resupplying previously purified liquid towards said unit to get into contact with inflow side of the membrane and to dissolve any soluble contaminants the might have previously been deposited on the inflow side of the membrane; and
-discharging said resupplied liquid together with said dissolved contaminants.
12. The method as claimed in claim 11, wherein said pas¬ sage of said liquid to be purified is applied with a pres¬ sure that exceeds the one applied during the resupplying step.
13. The method as claimed in claim 12, wherein said pu¬ rifying unit is a reverse osmosis unit and said discharging step relates to the liquid rejected by said membrane.
PCT/IB1994/000429 1993-11-26 1994-11-23 Improved membrane type liquid purification system WO1995014524A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU11174/95A AU1117495A (en) 1993-11-26 1994-11-23 Improved membrane type liquid purification system

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
HU9303360A HUT71424A (en) 1993-11-26 1993-11-26 Mebranic water purification system and method for using thereof for purification of liquids
HUP9303360 1993-11-26

Publications (1)

Publication Number Publication Date
WO1995014524A1 true WO1995014524A1 (en) 1995-06-01

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HU (1) HUT71424A (en)
WO (1) WO1995014524A1 (en)

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CN103657424A (en) * 2012-09-20 2014-03-26 山东康辉水处理设备有限公司 Built-in system cleaning and disinfecting device of ultrapure water machine
WO2016049504A1 (en) * 2014-09-26 2016-03-31 Staubach Barror Water Systems, Inc. Water recovery system, assembly and method for use of retentate recovered from membrane-based filtration devices
WO2016089890A1 (en) * 2014-12-01 2016-06-09 Organic Fuels Algae Technologies, LLC Method of cleaning a membrane contactor

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Also Published As

Publication number Publication date
AU1117495A (en) 1995-06-13
HUT71424A (en) 1995-11-28
HU9303360D0 (en) 1994-03-28

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