CA1180826A - Water purification system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A filter device for removing organic contaminants from water comprises a filter housing having an inlet for water at one end and an outlet for water at an opposite end and three layers of filter material contained in the housing. The first layer is a hydrophobic organophilic silicalite capable of functioning as a molecular seive and of adsorbing molecules as large as benzene. The second layer comprises a type I, strong base anion exchange resin of high porosity and high capacity while the third layer comprises activated carbon. The three layers are arranged one after another in series. Preferably the first layer is S-115 silicalite while the second layer is a copolymeric matrix made from styrene divinylbenzene. In the preferred embodiment the first layer of material is adjacent to the inlet.

Description

This invention relates to ~ilter devices ~or removing organic contaminants from water~
The problem of organic contaminants in domestic water supplies is well recoynized at the present time.
Some of these contaminants are quite dangerous although they may be present in drinking water in only a minute amount. It will be appreciated that it is difficult for authorities and scientists to determine the long-term harrnEul effects, if any, of these contaminants on huma lG beings, particularily in view of the fact that there are a wide variety of such materials and the particular contaminants in any given drinking supply can vary from one community to another.
In an article entitled "Water Filters" published in Consumer Repor';s, February 1983, a number of existing water filtration systemc; and devices are described. It is recognized in this article that the ~nown filters can help improve the taste or smell of the drinking water but not all are effective at controlling more dangerous contaminants. According to the same article more than 700 organic chemicals have been identified in drinking water and some of them are suspected cancer-causing agents.
Activated-carbon water filters are widely used to clean up water in bottling plants. On a more modest scale, carbon filters are used in the home -to filter tap water, Some domestic water filters are attached to the faucet of the sink while others are installed in the cold-water line which may lead to a ~aucet.

Fllters using carbon only may be una~le to remove some danyerous organic cornpounds that are pre.sent in drinking ~ater or drinkin~J supplies. As an exan~ple of contaminants -that exist in drinking water, -the fol1o~i.ny list of organic compounds and the quantity thereof was published in Homemakers m~gazine in March 1983. The list was compilecl by the organ:Lzation known as Pollution Probe and it is based on a samp:Le of water from Lake Ontario taken at a Toron-to, Ontario location.

Aromatic Hydrocarbons (parts per billion) Benzene .33 ppb Toluene .10 ppb E-thylbenzene Trace 15 O-Xylene Trace M-Xylene Trace P-Xylene Trace Pesticides .__ BMC .008 ppb 20 Lindane .003 ppb DDE .002 ppb Dieldrin .001 ppb PCBs .001 ppb Trihalomethanes 25 Chloroform 5.9 ppb Bromodichloromethane 7.5 ppb Chlorodibromomethane 1.8 ppb ~ _ 4 _ Filters that ernploy filter materials other than or i~ addition to activale-1 carhon are known. For exarnple U.S. patent 4,305,826 issued r)ecember 15, lg81 to Moses describes and illustrates a multi-layereA filter for softening and filtering water. The first layer comprises particles of activated carbon, the second layer consis~s of beads of an orgar.ic ion cation exchange resin, the third layer is made up of granules of sodium aluminum silicate, and the fourth layer consists of filter sand. The layers are arranged vertically in a tank~ The second and third layers of this filter act to soften the water. In addition the zeolite granuals in t:he third layer according to the patent will filter out most particles in the water whose size is greater than 20 microns.
Earlier U.S. patent 3,266,973 issued August 16, 1966 to Richard P. Crowley describes a method of preparing paper stock which has an affinity for particular materials.
During the manùfacturing process finely divided zeolite crystaline molecular sieve particles are added to the pulp which is then formed into a sheet and dried. The product described in the patent can be used as filter paper capable of removing particles, gases and the like of a particular size and dimension from al fluid stream. In one embodiment the molecular sieve particles are employed in combination with water insoluble ion exchange resins to incorporate a combination of ion exchange and adsorbent properties into the fibrous material.

The filter device described herein employs at least three different filtering ma~erial~ and thi~ enables the device to remove a wide range of organic materials from water. The preferred filter device i5 easy to conSitruct and can be produced at a relatively low cost. Accordingly it is believed that the device is particularly suitable for home or domestic use. Because the purchase cost of the device is reasonably low, the homemaker need not regenerate the filter materials although this could be done with a large filter system such as one that might be used by a commercial op~ration or a utility~
According to the present invention a filter device for removing organic contaminants from wa~er comprises a filter housing having an inlet for water at one end and an outlet for water at an opposite end and three layers o~ filter material~ The first layer comprises a hydrophobic, organophilic ~i~icalite capable of functioning as a molecular sieve and oi~ adsorbing molecules as large as benzene. The second layer comprises a type I strong base anion exchange resin of high porosity and high capacity while the third layer i8 activated carbon. 1~e three layers are arranged in series in the housing.
In a particularly preferred embodiment the irst layer is S-115 silicalite, a crystalline silica material produced by Union Carbide. The second layer is Dowex*-ll resin which is a copolymeric matrix made from styrene divinylbenzene.

* Trade Mark i Furthe~ features and advantages wil:L become apparent from the followin~ detaileci description ~aken ir conjunction with the accompanyiny drawings wherein:
Figure 1 is a side view of one embodiment of the filter device;
Figure 2 is a sectional view taken along the line II-II of Figure l; and Figure 3 is a graph illustrating the flow dependency of the filter of the presen~ invention.
Referring to F:igure 1 which is an illustration of one preferred embodiment of the present invention designed for domestic use, a filter device 10 for removing organic contaminants from water :includes an elongate filter housing 12, This housing includes a relatively long, tubular main section and two end caps 16 and 18. Each end cap may be provided with an intregal half inch nipple 20~
22 adapted for connection in a cold water supply line such as one supplying a faucet where drinking water is obtained, In the i].lustrated embodiment the nipple 20 forms an inlet for water while the nipple 22 forms an outletO Thus water leaving the outlet 22 would be substantially deconta~minated by the fi].ter device and would be available to be dispensed out of a faucet.
The illustrated filter housing can be made frorn standard plumbing parts and thls permits the cost to be kept relatively low. Both the main section 14 and the end caps can be constructed from inexpensive polyvinyl c:hloride.
One of the end caps such as the cap 18 can be permanently glued to the main section i.n a well known manner.

Preferably the other cap 16 is removable in order that the con-tents of the filter device can he removed for regeneration or replacement~ In the illustrated emhodiment the cap 16 is simply threaded onto ~he threaded end of the main section 14 and thus can be removed by simply rotating the end cap relative to the main section. In one preferred embodiment intended ~or domestic use the main sec-tion is constructed of one and a ~half inch diameter pipe and the overall length of the device measured between the outer ends of the two nipples i, approximately 26".
Preferably in order to prevent the possible escape of filter material out the outlet 22, a screen member or perforated disk 24 is provided in the housing adjacent to the inner end of the nipple 22.
The present filter device is constructed with at least three layers of filter material indicated at 26, 28 and 30~ The layer closest to the inlet is composed of a hydrophobic, organophilic silicalite capable of functioning as a molecular sieve and of adsorbing molecules as large as ~0 benzene. I'his rnaterial forms the thinnest layer of the three. The second layer comprises a type I, strong base anion exchange resin of high porosity and hlgh capaci-ty.
Although this layer is substantially thicker than the flrst layer, in a preferred embocliment its length L2 is considerably less than th~ length L3 oE the third layer 30. The third layer is composed of relatively inexpensive and well known actlvated carbon. As can be seen from Figure 2 the three layers 26, 28 ancl 30 are arranged in series so that water entering the inlet must pass through each of the layers in c,rder to reach the outlet a'c I:he nipple 2 2 .
Turning no~ t.o a more detailed description o the material.s formin~ each of the three :I,a~ers in this fi,lter 5 clevice an~ the func-t:ion thereof the preferred silica1ite used to form the first layer is that sold by Union Carbid~
under trade name S-115 . This material is a crys-ta:l, line, silica material which exhibits characteristics of molecular sieves~ Its composition is SiO2 and it is more than g9%
10 pureO At ambient temperatures S-115 silicalite will adsorh molecules as larye as benzene (kinetic diameter 5.~35 i~) hut re jects molecules larger than 6 A). Unlike aluminos.ilicate zeolite surfaces, S-115 silicalite has a very low selectivity for the adsorption of water and a very high 15 preference for the adsorption of organic molecules smaller than its lirniting pore size. Because the process of adsorption hy this material is irreversihle under normal conditions (for example the conditions that would be encountered during household use o:~ the filter device ) 20 removal of organi.cs having a small molecular weit~t is assured for at least a considerable length o:E timeO
Moreover the removal of these organics can help to protec t the other two layers o:f-' filter rnaterial which could he damaged by the presence of -trihalomethanes, phenol 25 derivatives and other nnaterials that might be present in the water supply and that are adsorhed by the s.ilicalite.
It will be appreciated by those skilled in the art that the other filter materials used in the present :Eilte:r are flow-dependent while the silicali te layer is not under normal 0~

conditions tpressure and temperat~re) because the adsorption of the organic materials is perrnanent. Thus a change in the rate of flow of water through the filter device will not remove the adsorbed materials from the silicaLite and brlng them back into solution.
Turning now to the second layer of filter material, the preferred anion exchange resin is Dowe~-ll which is a type 1, strong base resin of high porosity~
Such a material removes organics from the water in two different ways. The first is an actual ion exchange which occurs with organics containing carboxyl groups. The second methocl is adsorption of organics on the porous surface of the resin beads by a mechanism based on Van-Der Waals forces.
A~ an example of the type of material that can be removed using Dowex*-ll, humic acids can be removed as they have at least one carboxyl group~ An acid of this type will react chemically with the resin even after the active sites on the resin have been exhausted by reaction with such materials as silicates, carbonates and other inorganics. The reason for this is that the resin has a higher affinity towards organic materials than to inorganics~ 'Fhe organic thus replaces the inorganic which may very well be a harmless material in any event.
The aforementioned second method by which the resin removes organic materials is a purely physical phenomenom. I'here is no formation oE a covalent bond.

*Trade Mark .. . .
i

2~

Another preferred anion exchange resin that can be used in the present filter device i5 sold unaer the trade name Ionac* A~642. This material i5 a type 1, strong base macroporous resin. It is highly efficient and durable 5 and has a high capacity. It can be obtained from the Ionac Chemical Company.
It will be appreciated by those skilled in the art that the anion exchange re~in will remove many contaminants that are not adsorbed by the first layer. In particular it will remove organic materials whose size exceeds that of benzene. Although some of the organic materials captured by the second layer would likely be caught by the third layer comprising activated carbon, certainly not all of them would be and moreover this second layer of filter material is less flow dependent than the third layer of activated carbon. Thus the use of this second layer contributes to the overall efficiency of the filter device.
The third layer 30 comprising activated carbon polishes the product. In other words it will remove any disagreeable smell from the water as well as any bacl taste that might exist including residual chlorine~ The carbon also ca-tches suspended particles that manage to pass through ~he city's filtration plant. Finally the carbon will catch organics that were not adsorbed or otherwise removed by the ~irst kwo layers of the fil-ter. The efficiency and capabili-ty oE ~he third layer is increased by making the distance ~3 as long as practically possible .

*Trade Mark It is well recognized t'hat adsorption in activated car'bon i5 an important tool for water purification and this appLies especially to dissolved organic substances which are responsible for taste or odour or may actually be of an irritating or poisonous nature.
Activate~ car'bon is capable of removing some substances by catalytic reaction. For example chlorine is removed in this manner by activated carbon. Some kypes of particulate matter are removed by carbon by a mechanical filtration action.
Capacity tests have been run cn a filter device constructed in accordance with the present invention and containing about 500 grams of activated carbon, 100 grams of Dowex*-ll resin and 40 grams o S-115 silicalite. These tests have shc~wn that there is no breakthrough of the filter materials for a run of up to 800 irnperial gallons of water. However the filter is flow dependent as illustrated by the graph of Figure 3. The graph illustrates the ability of the filter to remove contaminants over thle pra~tical ran~3e or the size of the filter that was tested.
The testing for capacity and flow dependency was done by monitoring absorbancy at 254 nm using a Pye-unicam UV
Spectrophotometer. Figure 3 illustrates that the ability o the filter device to remove contaminants was excellent at a flow rate of up to 200 millilitres per minute.
However this ability decrea,sed at a uniform rate as the * Trade Mark .

~f~8f~

flow rate WclS increased t:o 800 milliliters per minute but even at the latter rate t,he percentage of contarninants removed is corlsiderable. The horizontal dash line rl~nning across the t:op of the graph represents the quantity of contaminants in the unfi].tered tap water which was used for the tests. The tests were carried out at 254 nanometers because the absorbance at: this level is accepted by those working in t.his art as a rough measure oF organic rnaterial.
~ Th.e filter of t:he present invention 'nas been tested to determine its efficiency in the removal of organic material from the ordinary tap water. The sample tap water that was used was from the city of Toron-to water system, which water contains organic materials amounting to around 4 ppm. This come~; as a rough estimate from 2 ppm of total organic carbon as proven by tests. The test results on this tap water were a~i follows:
Sample Identification TOC mg~l tap water l.77 aEter filter water 0.32 The letters TOC represent total organic carbon.
The test was carried out by an independent testing organization and it revea,ls that the present filter is capable oE removing 81 ]./'2% of organic materials from tap water. It will be appreciated that a removal of this high percent of contamination could very well be of considerable benefit to users of -the app]icant's filter device.

2~

For comparison purposes tests were also conducted to determine t,he efficierlcy of a filter device employing only activated carbon and another filter employing both activated carbon and a suitable ion exchange resin. Both filters performed less efficiently ~han the filter device of the present invention and in fact the carbon on],y filter was considerably less efficient as indicated by the following resul-ts:
ACTIVATED CARBON ONLY
10 Sample Identification TOC mg/L
tap water 2.15 after filter water 1.97 As can be seen from the above figures t'he filter device employing activat,ed carbon only was able to remove only 8% oE the total organics. Improved results from a carbon filter could probably be obtained by altering the -filter or the conditions of use. Nevertheless carbon filters suffer from other deficiencies including the fact that adsorption can be t:emporary and can be reversed. For example a sudden increase of flow through the filter or an interrupttion in the flow and subsequent re-estab]ishment thereof ecln cause adsorbed molecules to be released from the pores of the filter mat,erial and to re-enter the water.
A test on -the filter device employing activated carbon together with an ion exchange resin produce -the following results:

CA~BON AND RESIN F'ILTÆR
______t_ ication TOC rn~/L
tap water 2~15 after filter water ~.6 Thus this test resulted in a 72~ removal of organic cont:aminants from the tap water. Although this results is a considerable improvement over the result produced by the carbon only filter~ i~ is clearly not as good as the filter of the present invention. Moreover it should be kept in mind that the almost 10% improvement provided by the filter device of the present invention may siynify that important and dangerous contaminants are being removed substantially from the water while they are not being removed by the filt,er employing only two filter rnaterials.
Although it may not be practical for small filters intended for home use, it is possible to regenerate the filter rnaterials used in the filter devi,ce of the pcesent invention. If the present filter device was used by a utility or a large commercial operation, it would of course be constructed on a much larger scale than that indicated for a domestic filter device. ~lowever the commercial filter would be const,ructed in essentialLy the same manner as that illustrated in the drawings. In many commercial applications it would be practical to remove one end of the filter device and remove the filter matecials for regeneration. This possibility is indicated in Figure 2 by the threads 32 on the end caps 16. The end oE the main section 14 is also threaded in order to detachably receive the end cap.
Regeneration of the silicalite i8 carried out by the use of solvents and subsequent evaporation o~ the solvent from the material~ Other known techniques are also available. The preferred resin Dowex* -11 can be regenerated by means of a brine and HCl treatment. A salt solution subjects the resin to different osmotic pressures and different surface tens:ions. The effect is to counteract the Van-Der Waals forces so that the organics are released. In practice this brine treatment is accompanied by the injection of hydrochloric acid which regenerates the active sites of ~he resin and releases from them the carboxyl-containing molecules. In each case the removal effect is permanent under normal conditions.
The activated carbon material is the least expensive material and it may be more practical in many applications to simply rep]ace this material with new activated carbon rather thzln attempt to regenerate used material. However the service life of activated carbon can in some cases be extended by means of a steam treatment.
Objections have been raised in the past to the use of adsorbing filters on the grour~lds that there may be a health hazard due to possible bacterial growth and their service life can be rather limited because their ability to function terminates when they reach the saturation point.
With respect to the first objection, a filter constructed in accordance with the pre~ent invention was left in a wet state for about two and a half weeks and then treated with a countercurrent flow of tap water having about 0O08 ppm *Trade Mark -- 1.6 -of free chlorine. After al].owing the filter bed to settle, rinse samples were taken and subjected to BOD tes~s which showed negative every t.ime. For domestic use the filter can be combined with a bacteria kill.ing device such as the known one using ultravi.olet light.
With respec-t to the possible saturation of -the present ilter, it shou.ld be appreciated tha-t every fil-ter of a certain si.ze has a safe service life before saturation will occur. However a problem can occur if the filter is subjected to vigorous shaking which can. release trapped organics into effluent. It ic2 submi-tted however tha-t sa-turation should not be a problem with -the present filter if proper care is taken by the user and it is not used beyond its recommended service lifeO Proper use of -the filter would include initial rinsing in, placing the filter at one steacly angle or position and an occasional backwash~

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A filter device for removing organic contaminants from water comprising a filter housing having an inlet for water at one end and an outlet for water at an opposite end, a first layer of filter material comprising a hydrophobic, organophilic silicalite capable of functioning as a molecular sieve and of adsorbing molecules as large as benzene, a second layer of filter material comprising a type I, strong base anion exchange resin of high porosity and high capacity, and a third layer of filter material comprising activated carbon, said three layers being arranged in series in said housing.

2. A filter device according to claim 1 wherein said silicalite is S-115 silicalite.

3. A filter device according to claim 1 wherein said resin is a copolymeric matrix made from styrene divinylbenzene.

4. A filter device according to claim 1, 2, or 3 wherein said housing is elongate with said first layer of filter material provided adjacent to said inlet.

5. A filter device according to claim 1, 2, or 3 for domestic use wherein said housing is constructed of polyvinyl chloride pipe and a screen member is provided in said housing and over said outlet to prevent escape of carbon through said outlet.

6. A filter device according to claim 2 wherein said resin is Ionac A-642.

7. A filter device according to claim 3 wherein said resin is Dowex-ll resin.

8. A filter device according to claim 1 wherein said resin is a gel-type and can be regenerated.

9. A filter device according to claim 1, 2, or 3 containing at least 40 grams of silicalite, at least 100 grams of resin and about 500 or more grams of said carbon.

10. A filter device according to claim 1, 2, or 3 including means for opening up said housing to permit removal of said filter materials.