HK1061539A - Method and apparatus for treatment of drinking water - Google Patents

Description

Method and apparatus for treating drinking water

Technical Field

The present invention relates to a method and apparatus for treating drinking water, and more particularly to a treatment method utilizing a combination of a regenerable ion exchange resin and an immersed membrane filter in a single treatment tank.

Background of the invention

Raw water can be treated and purified by various methods in order to make it potable. The particular contaminants of a given water stream are suitable for use with a particular treatment process. Ion exchange resins are used in water treatment systems to remove soluble compounds, some of which are organic. Microfiltration and ultrafiltration membranes are used to remove particulates. For aqueous streams containing both compounds, a first treatment must be used followed by a second treatment. The need to employ two separate steps can be time consuming, require additional equipment, and increase the overall cost of the processing system. Accordingly, there is a need for an improved drinking water treatment system that is capable of removing particulates and soluble organic compounds and that is cost and time efficient compared to existing systems.

U.S. Pat. No.6027649 to Benedek discloses a process for utilizing ZEWEED in a single reactor tank^A method for treating drinking water in combination with a flocculant by mixing the filter with the flocculant in a reactor tank and keeping the filter in suspension with air bubbles. The flocculant will become a remover of organic matter, pigments, bacteria, cells (cysts) and other impurities. The use of the flocculant described by Benedek requires that the pH be maintained in the range of 5-9. This requires the addition of an acid or base to the raw water in order to maintain the desired pH range. Although Benedek describes the use of a single tank of flocculant in combination with a membrane filter, the use of flocculant to remove organic matter requires subsequent disposal of the remaining flocculant. Thus, not only must the remaining flocculant be properly disposed of, but new coagulant must be provided to the reactor tank in order to form the desired flocculant. Benedek also discloses that activated carbon is preferably added to the reactor tank to remove dissolved organics. However, as with flocculants, this also creates problems with disposal of the remaining activated carbon and requires replenishment of the reactor tank with fresh activated carbon.

Daly U.S. APatent No.6120688 relates to a method for purifying water, which also makes use of ZEWEED^A membrane filter. In particular, Daly describes the use of ZEWEED first^The filter performs particulate removal and then filters the water using reverse osmosis. While Daly eliminates the flocculant and activated carbon disposal problems in Benedek, Daly requires two processing steps, which increases the size of the equipment and the cost required.

The present invention is directed to overcoming one or more of the problems set forth above.

Brief introduction to the invention

A first aspect of the invention is a method for treating drinking water. Raw water is supplied to the treatment tank. Ion exchange resin is added to the treatment tank to form a raw water/ion exchange resin mixture. The treated water is discharged from the treatment tank through the membrane filter. Preferably, the ion exchange resin is a magnetic ion exchange resin. The magnetic ion exchange resin is separated from the raw water/ion exchange resin mixture by a high magnetic field gradient filter. Then, the separated ion exchange resin is preferably regenerated and then supplied again to the treatment tank. The ion exchange resin may be regenerated in an external counter-current column. Alternatively, the regeneration step is performed in the treatment tank by adding a salt solution to the treatment tank. The regenerated ion exchange resin is then separated from the raw water/regenerated ion exchange resin mixture.

Another aspect of the invention is an apparatus for treating drinking water. The apparatus includes a treatment tank for receiving raw water. An ion exchange resin supply is operatively connected to the treatment reservoir for providing ion exchange resin to the raw water in the treatment reservoir. The membrane filter is operatively connected to the treatment basin to separate particulate matter from treated water discharged from the treatment basin through the membrane filter. The apparatus may further include a resin separator operatively connected to the treatment reservoir for removing the ion exchange resin from the ion exchange resin/raw water mixture. In this embodiment, the ion exchange resin is preferably a magnetic ion exchange resin and the resin separator is preferably a high magnetic field gradient filter. Preferably, the resin regenerator receives the ion exchange resin removed by the separator to regenerate the ion exchange resin by using a salt solution. Preferably, a conveyor is also provided for conveying the regenerated ion exchange resin to the ion exchange resin supply. The resin separator may be an external counter-current column that uses a salt solution to regenerate the ion exchange resin. In a more preferred embodiment, an aerator is provided in the treatment basin to agitate the ion exchange resin/raw water mixture in the treatment basin.

The apparatus and method for treating drinking water of the present invention combines two separate treatment techniques in a single tank to remove soluble contaminants and particulates in a single treatment process. The apparatus and method use ion exchange resins that can be separated from the raw water/ion exchange resin mixture and then regenerated for reuse. The method both extends the useful life of the ion exchange resin and reduces waste and disposal problems encountered in prior art water treatment systems.

Brief description of the drawings

Fig. 1 is a schematic diagram of a drinking water treatment system of the present invention.

FIG. 2 is a simplified schematic of an embodiment of the invention in which regeneration of the resin is carried out by a countercurrent column.

FIG. 3 is a simplified schematic of an embodiment of the present invention in which regeneration of the resin is performed in a treatment tank.

FIG. 4 is a schematic diagram showing a basic water treatment process.

FIG. 5 is a schematic diagram showing the film/resin treatment of the present invention.

FIG. 6A is a graph showing the effect of regeneration treatment bed volume on contactor resin concentration control using the mathematical model of the process shown in FIG. 1.

FIG. 6B is a graph showing the effect of regenerated resin contact time on control of contactor hydraulic residence time using a mathematical model of the process shown in FIG. 1.

FIG. 6C is a graph showing the effect of regeneration treatment bed volume on control of resin recovery using the mathematical model of the process shown in FIG. 1.

Description of The Preferred Embodiment

The drinking water treatment method of the present invention combines two separate technologies to remove natural organic matter and particulates in a single treatment process. This method is illustrated in figures 1, 2 and 3. Referring to fig. 1, raw water from a raw water tank 6 is introduced to a treatment tank 14 under gravity or by a pump 7. The absorbing ion exchange resin is added from the resin storage vessel 10 to a treatment tank 14 by a pumping system 11, the treatment tank 14 containing a submerged membrane filter 12. A suitable submerged filter is ZEEWEED^Film (ZENON Environmental, inc., ontario, canada). The ion exchange resin removes dissolved natural organic matter from the water, while the membrane filter removes particulates. The cell 14 is agitated by aeration by the aeration system 13 to suspend the ion exchange resin. The treated water is drawn from the hollow fibre membranes of the membrane filter 12 by means of the vacuum (outside/inside) generated by the pump 15 to the line 17 where it can be disinfected, stored and distributed.

Ion exchange resins have a limited capacity for adsorbing materials. When this capacity is reached, the resin must be discarded or regenerated. During treatment, a high concentration of ion exchange resin is formed in the treatment cell 14 and the ion exchange resin can be removed by gravity or by a pump 16. The spent ion exchange resin is then sent to a resin separator 18 where the ion exchange resin is precipitated from the remaining water at the resin separator 8. The ion exchange resin is then regenerated in a regeneration reservoir 20. Typically, regeneration is performed by treatment with a high concentration salt solution. The regenerated resin may be returned to the treatment reservoir 14 via line 23A by return pump 22 or transferred to the ion storage vessel 10 via line 23B.

In a preferred embodiment, the ion exchange resin is a magnetic ion exchange resin, such as MIEX manufactured by Orica Watercare, Australia^And (7) a DOC. Preferably, about 20mL of MIEX per liter of water is used^A DOC resin. At this point, the resin may be selectively removed from the membrane filter sump by using a high magnetic field gradient filter (HGMF)23 (shown only in fig. 2 and 3, but which may also be part of the system of fig. 1), which high magnetic field gradient filter 23 separates the resin from the water and other particulates in the sump.

Referring to fig. 2, in another embodiment, regeneration of the resin is accomplished by a countercurrent column 24 in which a salt solution is pumped upwardly through the countercurrent column 24 to remove organic matter from the resin. Regenerated resin is removed from the bottom of the column and can be returned to the treatment tank via line 30. The spent brine is processed through line 32.

Referring to fig. 3, in another embodiment, the membrane filter chambers are partitioned, salt is added, and agitated by air from an air agitation system 13 for regeneration. At this point, the bath solution is removed and passed through HGMF23 to resin reservoir 34.

In any case, the regenerated resin is returned to the membrane tank and the spent brine is suitably disposed of.

Because the ion exchange resin of the preferred embodiment is magnetic, it tends to accumulate and precipitate in the treatment basin 14. To overcome this tendency, the magnetic ion exchange resin is kept in suspension by an air agitation system 13. The air agitation system allows for significantly higher resin concentrations in the treatment tank. A suitable inflator is SWEETWATER^Linear piston air pumps are commercially available from Aquatic Eco-Systems, Inc. (Apopka, florida).

To further optimize the systemA mathematical model expressed in the mass balance of the resin was developed to determine when ZEEWED was used^Membrane and MIEX^Residence time and adsorption concentration in the DOC resin treatment tank. For comparison, also for the application of MIEX alone^The DOC resin and no film base treatment method was modeled (hereinafter referred to as "base method"). The values of the basic method are shown in table 1 and the values of the model are shown in table 2 and schematically represented in fig. 4. The basic method 40 includes a treatment or contact tank 42, raw water being fed into the treatment tank 42 via a conduit 44, and ion exchange resin being fed into the contact tank 42 from a resin supply 46. The resin supply 46 receives fresh resin from a fresh resin supply 48 and regenerated resin from a regenerator 50. Separator 52 serves to separate the ion exchange resin from the raw water, which is then suitably retained in the treatment basin, while treated water is output through line 54. The separated ion exchange resin is delivered to regenerator 50 via line 54 and the regenerated resin is delivered to the resin supply via line 58.

The amount OF water treated per day, TW, is 1 million gallons or 3785000 liters, which is the same as the amount OF raw water added to the system, RW, and the amount OF water output from the basin, OF. Separator underflow SU is the amount OF water leaving the separator, equal to the outflow from the cell multiplied by the resin concentration, subtracted by the resin loss, and then divided by the resin concentration by 30% (v/v), or SU ═ OF (OF RC-OF RC) RL)/0.3. The resin RG fed to regeneration is equal to the outflow multiplied by the resin concentration multiplied by the percentage OF underflow regeneration, minus the resin loss, or RG ═ OF RC U-OF RC U r RL. The recovered resin RR is returned from the separator to the contact tank, equal to the outflow multiplied by the resin concentration minus the resin loss, minus the amount sent to regeneration, or RR ═ OF RC-OF RC × -RC-RG. The amount of regenerated resin returned to the resin supply device is equal to the amount of recovered resin. The fresh resin in the supply tank is a combination of fresh and regenerated resin. The fresh resin FR is equal to the amount OF resin that must be added to compensate for the amount OF resin at each stage outside the treatment tank, or FR OF RC-RR. The new resin VR is equal to the total amount OF resin that must be added to compensate for resin loss, or VR ═ OF RL.

Trees while regeneratingFat contact time CT_RIs the concentrate times the resin concentration and takes into account the resin loss and the amount of underflow sent to regeneration, or RC_R＝RI/[OF*RC-OF*RC*(1-RL)*U]. The total amount of resin in the contact cell, RI, is equal to the amount of treated water in the contact cell multiplied by the contact time, CT, multiplied by the resin residence time, or RI, RW, CT, RT. The regeneration treatment bed volume BV is the resin contact time at regeneration times the raw water amount divided by the total resin amount in the contact tank, or BV RC_RRW/RI. The resin residence time RT is the product OF the total amount OF resin in the contact cell divided by the outflow, resin loss and resin concentration, or RT ═ RI/(OF RL RC).

TABLE 1 values used in the basic Process model

Variables of	Marking	Value of
			Contactor resin concentration	RC	6mL/L
Contact time	CT	30 minutes
			Underflow as regenerated%	U	10％
Resin loss in the separator	RL	0.10％
			Handling traffic	OF、RW、TW	1 million gallons per day

TABLE 2 basic Process model

Fluid flow	Flow rate	Resin concentration	Resin @ 100% per day
					L/day	％v/v	L/day
1. Raw water	3,785,000	0	0
				2. Resin supply	2,291	100	2,291
3. Outflow from the contact tank	3,785,000	0.60	22,710
				4. Separator underflow	75,624	30	22,687
5. Treated water	3,785,000	0.0006	23
				6. The regenerated resin	2,269	100	2,269
7. Recovery of resins	20,419	100	20,419
				8. Regenerated resin	20,419	100	20,419
9. Novel resins	23	100	23

The model using the values in table 3 is a model employing the method of the present invention using a membrane and an ion exchange resin (hereinafter referred to as membrane/resin method). The values of the model are shown in table 4 and are schematically represented in fig. 5. Briefly, the schematic diagram 5A shows a membrane treatment basin 62 including a membrane filter 63. The raw water enters the membrane treatment tank through a conduit 64 where it is mixed with resin from a resin supply 66. The water drawn through the membrane filter 63 exits as treated water at line 68. The ion exchange resin/raw water mixture is withdrawn from the membrane treatment tank through line 70 to a resin separator 72. The wastewater is discharged at conduit 74 for proper disposal. The separated resin is passed through line 76 to regenerator 78 for regeneration. The regenerated resin is transferred through a conduit 80 to the resin supply 66 where it can be mixed with or replenished with new resin from a new resin supply 82 at the resin supply 66.

The model is based on a treated water flow TW of 1 million gallons per day or 378500L/day. The concentrate flows from the treatment tank to the resin separator. The concentrate is defined as the amount of treated water multiplied by the appropriate amount of loss MR through the membrane, or C ═ TW (1-MR). The raw water entering the tank was equal to 3785000L/day plus the amount of concentrate recovered C. The treated concentrate TC is discharged from the system and is equal to the amount of resin lost from the concentrate, or TC ═ C × RC × RL. The separator underflow amount is the amount of water leaving the resin separator. The separator underflow SU is equal to the concentrate fed to the resin separator multiplied by the resin concentration, taking into account the resin loss, and divided by the resin concentration by 30% (v/v), or SU [ [ C ] RC (1-RL) ]]/0.3. The separator underflow amount is divided into two parts: the regenerated resin RG and the resin RR recovered to the treatment tank. RG is the resin in the concentrate and takes into account resin losses and underflow U sent to regeneration, or RG ═ C RC — (1-RL) U. The recovered resin RR is the separator underflow minus the amount to be recoveredRaw resin, or RR ═ C RC ═ C (1-RL) - (C ═ RC ═ U)]RG. The regenerated resin sent to the resin supply device is the same resin as the resin to be regenerated. The fresh resin fed to the tank is a combination of fresh and regenerated resin. The fresh resin FR is equal to the amount of resin that must be added to compensate for the amount of resin at each stage outside the treatment tank, or FR-C RC-RR. The new resin VR is equal to the total amount of resin at each stage outside the treatment tank minus the amount of regenerated resin, or VR ═ FR-RG. Resin contact time CT at regeneration_RIs the total resin in the contact tank divided by the concentrate times the resin concentration and taking into account the resin loss and the underflow amount to regeneration, or RC_R＝RI/[C*RC*(1-RL)*U]. The total amount of resin in the contact cell, RI, is equal to the amount of raw water in the contact cell multiplied by the contact time, CT, multiplied by the resin residence time, or RI, RW, CT, RT. The regeneration treatment bed volume BV is the resin contact time at regeneration times the amount of treated water divided by the total amount of resin in the contact tank, or BV RC_RRW/RI. The resin residence time RT is the total amount of resin in the contact tank divided by the treatment concentrate, or RT ═ RI/TC.

TABLE 3 values used in film/resin treatment

Variables of	Marking	Value of
			Contactor resin concentration	RC	25mL/L
Contact time	CT	12 minutes
			Underflow as regenerated%	U	40％
Loss of resin	RL	0.10％
			Membrane treatment recovery	MR	95％
Treated water flow	TW	1 million gallons per day

TABLE 2 basic Process model

Fluid flow	Flow (L/day)	Resin concentration (% v/v)	Resin @ 100% per day
				1. Raw water	3,974,250	0	0
2. Resin supply	1,895	100	1,895
				3. Concentrate	189,250	2.5	4,731
4. Separator underflow	15,755	30	4,727
				5. Treated water	3,785,000	0	0
6. The regenerated resin	1,891	100	1,891
				7. Recovery of resins	2,836	100	2,836
8. Regenerated resin	1,891	100	1,891
				9. Novel resins	5	100	5
10. Treatment of concentrates	5	100	5

The results of a comparison of the two methods in table 5 show the improvement of the method of the invention.

TABLE 5 comparison of results for the basic Process and the film/resin Process

Variables of	Marking	Basic treatment	Film/resin treatment
				Resin contact time (hrs) upon regeneration	CTR	5	10.5
Bed volume of regeneration treatment	BV	1668	2002
				Total amount of resin in contact cell (L)	RI	473	828
Resin residence time (day)	RT	21	175
				Fresh resin dose (mL/L)	FR	0.61	0.50
New resin dose (mL/L)	VR	0.0060	0.0012

The resin contact time during regeneration increased from 5 hours to 10.5 hours. The volume of the treatment bed in the regeneration step also increased from 1668 to 2002. The total amount of resin in the contact cell increased greatly from 473L to 828L. Because the design of the system allows for multiple resin recoveries, the resin contact time will be significantly higher than the water retention time, HRT (retention time of the water to be treated in the treatment system). Resin residence time also increased greatly from 21 days to 175 days. Meanwhile, the dose of the fresh resin is reduced from 0.61mL/L to 0.50mL/L, and the amount of the new resin is also reduced from 0.0060mL/L to 0.0012 mL/L.

The output of the film/resin process model when the input is varied is also shown in fig. 6A, 6B and 6C. FIG. 6A shows the effect of regeneration treatment bed volume on contactor resin concentration control. FIG. 6B shows the effect of regenerated resin contact time on contactor hydraulic dwell time control. FIG. 6C shows the effect of regeneration treatment bed volume on resin recovery control.

Devices employing some or all of the advantageous principles of the present invention may be used in a wide variety of specific systems. The water treatment systems of fig. 1, 2 and 3 are typical and schematic and are not to be considered as a selection of the scope and implementation of the present invention.

Claims (16)

1. A method for treating drinking water, comprising:

a) supplying raw water to a treatment tank;

b) adding an ion exchange resin to the treatment tank to form a raw water/ion exchange resin mixture; and

c) the treated water is drained from the treatment tank through the membrane filter.

2. The method of claim 1, wherein: the ion exchange resin is a magnetic ion exchange resin.

3. The method of claim 1, further comprising: the raw water/ion exchange resin mixture is agitated sufficiently to keep the ion exchange resin in suspension.

4. The method of claim 1, further comprising: the ion exchange resin is separated from the raw water/ion exchange resin mixture.

5. The method of claim 2, further comprising: the ion exchange resin is separated from the raw water/ion exchange resin mixture using a high magnetic field gradient filter.

6. The method of claim 5, further comprising: the ion exchange resin is regenerated.

7. The method of claim 6, further comprising: the regenerated ion exchange resin is supplied to the treatment tank.

8. The method of claim 6, wherein: the regeneration step is carried out in an external countercurrent column.

9. The method of claim 6, wherein: the regeneration step is carried out in the treatment tank by adding a salt solution to the treatment tank.

10. An apparatus for treating drinking water comprising

A treatment tank for receiving raw water;

an ion exchange resin supply source operatively connected to the treatment reservoir for providing ion exchange resin to the raw water in the treatment reservoir;

a membrane filter operatively associated with the treatment basin for separating particulate matter from treated water discharged from the treatment basin through the membrane filter.

11. The apparatus of claim 10, further comprising: a resin separator operatively connected to the treatment reservoir for removing the ion exchange resin from the ion exchange resin/raw water mixture.

12. The apparatus of claim 11, wherein: the ion exchange resin is a magnetic ion exchange resin and the resin separator is a high magnetic field gradient filter.

13. The apparatus of claim 11, further comprising: a resin regenerator that receives the ion exchange resin removed by the separator;

14. the apparatus of claim 13, further comprising: means for transferring regenerated ion exchange resin from the resin regenerator to the ion exchange resin supply.

15. The apparatus of claim 13, further comprising: the resin separator is an external counter-current column that uses a salt solution to regenerate the ion exchange resin.

16. The apparatus of claim 10, further comprising: an aerator in the treatment tank for agitating the ion exchange resin/raw water mixture in the treatment tank.