Water purification means and method

A novel filtration system for purifying a relatively small volume of water, and especially for removing objectionable tastes and odors from drinking water. An inverted container of the water to be purified is supported above a filter which in turn is supported above a bottom container for receiving the effluent from the filter. The upper container is provided with an outlet tube which extends into the filter and is provided with means for regulating the flow of water to the filter. The filter holds a disposable filter medium in the form of a thin "sandwich" of two outer sheets of readily permeable material and a thin inner layer of activated carbon particles disposed uniformly between the two outer sheets. In operation, water flows from the upper container through the filter into the bottom container, the rate of flow of water from the upper container being controlled automatically by the level of water in the filter. A simple and inexpensive process for purifying a relatively small volume of water, and which is especially suitable for a one-time use of the disposable filter medium component, is thus provided.

This invention relates to the purification of water. It comprises a new and 
useful water purification process and apparatus and article of manufacture 
for carrying out the process. 
Much attention has been given, especially in the last few years, to the 
quality of community water supplies. While the bacteriological quality of 
these supplies is in general excellent, many of them contain objectionable 
tastes and odors, and some contain at least trace amounts of chemical 
substances which may be hazardous to human health. 
The most common, and almost universal, source of objectionable taste and 
odor in water is chlorine. With few exceptions, practically all community 
water supplies in the United States are disinfected with chlorine, and a 
small residue of chlorine is purposely left in, or added to, the water as 
it leaves the water plant and enters the community distribution system. 
The amount of this "residual chlorine" may be as much as 0.7 to 1.0 parts 
per million (ppm) as the water leaves the plant, but it usually drops to 
about 0.5 ppm or less in a distribution system of appreciable size by the 
time the water reaches the consumer's tap. The twofold purpose of the 
residual chlorine is to give evidence that the water has been adequately 
disinfected, and to provide protection against minor contamination in the 
distribution system. The absence of residual chlorine in the distribution 
system is usually cause for investigation and possibly for concern. 
Besides chlorine, objectionable tastes and odors may be produced, 
especially in surface waters, by trace or larger amounts of organic 
substances--objectionable either in themselves, or in combination with the 
chlorine used for disinfection. Phenols, for example, are much less 
objectionable than the chlorophenols produced by their reaction with 
chlorine; and one of the compounds resulting from chlorination that is 
currently causing serious concern is chloroform, which has been shown to 
be carcinogenic in tests with rats. 
The agent that has been found most generally effective for removing the 
several types of objectionable tastes and odors mentioned, as well as 
certain other kinds of impurities--some of them possibly hazardous to 
human health--is activiated carbon, in either granular or powdered form. 
Beds of granular carbon, in suitably designed equipment, are extensively 
used for that purpose in a wide variety of industrial plants, especially 
in food and beverage plants. Until the last few years, community water 
treatment plants used powdered activated carbon almost exclusively, in 
connection with conventional treatment processes. The development of 
improved and practical methods for regenerating spent granular carbon, and 
the availability of attractive servicing and leasing plans, have led to 
renewed interest in and use of granular carbon in community treatment 
plants. 
The taste and odor due to residual chlorine, and/or the chlorinated 
compounds that may have been formed by chlorination of the water, are as 
objectionable in the home as they are in the industries mentioned since, 
besides making the water itself unpalatable to drink, they make it 
difficult or impossible to prepare good-tasting coffee, other beverages, 
and many foods. 
For removing residual chlorine and other objectionable taste and odors from 
water in the home, a number of small filter devices, typically employing 
small beds or pads of granular activated carbon, have appeared on the 
market. The typical device of this kind is connected into the cold water 
line in the kitchen or bathroom and is provided with a separate faucet for 
drawing off the water that has been filtered through the carbon. 
Aside from the effort and expense of installing devices of this sort, there 
is a much more serious objection to them, that is, that the carbon bed can 
unfortunately become an excellent breeding ground for the growth of 
bacteria and certain other organic substances. As a result, after a short 
initial period of use, the water leaving the filter may contain many more 
bacteria and much more other organic matter than the water entering it. In 
the case of a large, commercial activated carbon filter, frequent 
backwashing of the filter helps to prevent or delay the development of 
this contaminated condition and, if and when the condition does occur, 
methods have been devised, usually employing steam, hot water, or 
chemicals, to sterilize the carbon bed and restore it to its 
non-contaminated condition. It is obvious that none of these methods of 
sterilization is available or practical in the case of the typical small 
household filter connected to the cold water line. 
The importance of this factor can be appreciated from the fact that the 
purification capacity of a typical commercial activated carbon filter, 
especially for removing chlorine, is so relatively enormous that the 
carbon bed remains effective for at least a year or two before it needs 
replacement. It is easy to find the explanation for this extremely long 
active life, especially when residual chlorine is the principal or only 
impurity removed by the carbon. 
When chlorine is dissolved in water, it forms hydrochloric acid (HCl) and 
hypochlorous acid (HClO): 
##STR1## 
And, when this water is passed through an activated carbon filter, the 
hypochlorous acid reacts with the carbon, forming more hydrochloric acid 
and carbon dioxide: 
##STR2## 
Multiplying equation (1) by 2, and adding the resulting equation to 
equation (2): 
##STR3## 
The last line of figures above shows the relative weights of chlorine, 
water and carbon taking part in the reaction. From these figures it is 
evident that if the carbon (atomic weight 12) is 100 percent pure and 
completely reactive (probably never quite true in either case), 12 grams 
of carbon will react with 142 grams of chlorine (molecular weight 71), 
practically 12 times its own weight. If we assume further that the typical 
community water supply contains at the tap 0.5 parts per million, or 0.5 
milligrams per liter, of residual chlorine, then one gram (1,000 
milligrams) of our theoretically pure and completely reactive carbon can 
react with the 12 grams (12,000 milligrams) of chlorine contained in 
24,000 liters (a little more than 6,000 gallons) of that water--enough to 
supply a typical family of four with its water for drinking and cooking 
for about four years. Since the typical household activated carbon filter 
usually contains much more than one gram of carbon, the volume of water 
from which the 0.5 parts per million of chlorine may be removed is really 
enormous. 
The minute amount of hydrochloric acid formed in the reaction between the 
0.5 parts per million of chlorine and the activated carbon is negligible 
and it is immediately neutralized by the alkalinity always present in 
community water supplies and practically all natural waters. 
The practical point of the above calculation is that the activated carbon 
in a typical small household filter can become badly contaminated with 
bacteria and other organic growths long before its ability to remove 
chlorine is exhausted; the filter thus may contaminate, instead of 
purifying, the water passing through it. 
Many organic and inorganic compounds which do not react chemically with 
activated carbon are adsorbed by it. These compounds include not only 
those whose presence is evident because they produce color or 
objectionable taste and/or odor, but also those that may be present in a 
water that is perfectly clear, colorless, and free from objectionable 
taste and/or odor. While some of these compounds may be present in only 
minute or even trace amounts, the toxicity of some of them is great enough 
to cause concern. 
It is the basic objective of the present invention to utilize the 
advantages of activated carbon in water treatment while avoiding the 
disadvantages noted above. This objective is accomplished by treating a 
relatively small volume of water with a novel, inexpensive and disposable 
carbon-containing filter medium which is designed specifically to permit 
discarding it after a single use, and to perform the treatment in a novel, 
simple, and automatic manner. 
A principal object of the invention is a batch process for removing 
objectionable tastes and odors from a confined and relatively small volume 
of water, especially drinking water. 
Another principal object of the invention is a batch process for purifying 
relatively small volumes of water automatically and economically. 
Another object of the invention is a batch process for removing potentially 
hazardous organic compounds from a confined and relatively small volume of 
drinking water. 
A further object of the invention is an improved filter system for carrying 
out the processes of the invention.

The novel and disposable carbon-containing filter medium used in the filter 
consists essentially of a thin "sandwich" of two outer thin sheets of an 
inert, readily permeable material and a thin inner layer of activated 
carbon particles disposed uniformly between the two outer sheets. 
This "sandwich" filter medium may be formed in any suitable manner. Using 
the apparatus shown in FIG. 3 in the drawings, powdered activated carbon 
is mixed with water and a water-soluble or water-insoluble binder adhesive 
to form a fluid paste 5, and, by means of a feed roll 6 passing through a 
container 7 of the paste, continuously depositing a coating 8 of the paste 
on the under surface of a moving strip 10 of one of the outer sheets of 
permeable material. The other outer sheet 11 is then applied continuously 
and synchronously under the moving coated one. The "sandwich" 12 thus 
formed passes through compressing rolls 13--13 to a drying chamber 14. The 
web leaving the dryer 14 may be wound up in a roll form. Alternately the 
web may be formed into special shapes before or after drying. 
The method of forming the "sandwich" filter medium 12 may be varied in many 
ways, both as to materials and as to details of processing. The outer 
sheets 10 and 11 may be composed of any readily permeable water-insoluble 
material capable of holding back the particles of activated carbon and 
preventing their escape into the water being treated. I have found 
satisfactory for this purpose, loosely woven filter paper or cloth, paper 
towelling, porous plastic, etc. Scott brand towelling has been used. 
Whatman #1 filter paper available from B & R Balston, Ltd., England and 
qualitative filter such as Fisher Brand, coarse porosity (crimped) filters 
(200 ml/min./in..sup.2 with 2 inches head) available from Fisher 
Scientific Co. , may also be used. 
There is also a wide choice of materials serving as a binder and adhesive 
in forming the paste 5. Among those that may be used are starch, sodium 
carboxymethyl cellulose (CMC), water-soluble or water-insoluble resins, 
mixtures thereof, etc. Ther choice of a water-soluble or water-insoluble 
binder will depend on the type of filter medium desired. The advantage of 
a water-soluble binder is that it quickly escapes with the first flow of 
water through the filter, thus freeing additional surface of the activated 
carbon particles. The obvious disadvantage of a water-soluble binder is 
that the first volume of effluent will contain the binder, the ingestion 
of which in some cases may not be desirable, in which event the initial 
small volume of effluent should be discarded. 
Instead of aqueous mixtures of activated carbon, adhesive binder and water, 
I may use mixtures of non-aqueous solvents miscible with other binding 
materials. Alternatively, I may utilize as a binder a known 
pressure-sensitive or thermoplastic adhesive thereby avoiding the need for 
a final drying step. In using a thermoplastic resin adhesive as the 
binder, as in so-called "hot melt" operations, the operation is conducted 
at a temperature high enough to effect sufficient fluidity in the mixture, 
but below a temperature that would injure the outer permeable layers of 
the "sandwich". 
Still another method of forming the "sandwich" filter medium, which I 
consider somewhat less desirable than those already mentioned, is to brush 
or spray a thin layer of finely powdered activated carbon, without a 
binding material, on the upper surface of one continuously moving outer 
layer, and subsequently lay down the other outer layer in the manner 
previously described. 
The "sandwich" filter medium may be formed into any desired size and shape. 
For purposes of illustration, it is shown in the drawing as a folded 
filter disc 20 such as in common use with glass funnels in chemical 
laboratories. Other shapes may also be used to conform to the design of 
the apparatus in which it is to be employed. For example, the filter 
medium may be pre-formed with fluted sides and nested in various 
quantities in the same manner that paper filters for automatic electric 
coffee makers are preformed and nested. The general objective is to 
provide maximum filter surface consistent with that type of apparatus so 
as to permit maximum flow of water through the filter. 
The following two examples of aqueous mixtures of adhesive binder and 
activated carbon which may be utilized in the process of forming the 
"sandwich" filter medium 12 as shown in FIG. 3 of the drawing are given by 
way of illustration and without limitation: 
EXAMPLE 1 
______________________________________ 
Powdered activated carbon - 
10.0 parts by weight 
"Darco" "S-51" 
Powdered corn starch - 
4.0 " 
food grade 
Water 100.0 " 
______________________________________ 
"Darco" activated carbon is a product of ICI, United States. "Argo" corn 
starch is a product of Best Foods, a division of CPC International, Inc. 
The starch is mixed with about 12 to 15 parts of the water (cold) to form a 
thin slurry; this is then added with vigorous stirring to the remainder of 
the water which has been heated to boiling. Almost immediately a 
translucent paste is formed, embracing the entire volume of the mixture. 
The activated carbon is then added gradually, with continued stirring, 
until the carbon is distributed uniformly throughout the mixture which now 
has a fluidity suitable for use with the feed roll shown in FIG. 3. 
EXAMPLE 2 
______________________________________ 
Powdered activated carbon - 
20.0 parts by weight 
"Nuchar" 
Sodium carboxymethyl cellulose - 
2.0 " 
(CMC) 
Water 100.0 " 
______________________________________ 
"Nuchar" activated carbon is a product of Westvaco Corporation. CMC used is 
a product of Hercules, Inc. 
The activated carbon and CMC are thorougly mixed in the dry state. This 
mixture is added to the water at room temperature and stirred vigorously 
for several minutes until the swelling of CMC produces a paste with 
sufficient fluidity for use with the feed roll 6 (FIG. 3). 
Referring now to FIG. 1, this shows one arrangement for readily carrying 
out my invention in the home or field or elsewhere. Upper container 22 and 
lower container 23 are readily available half-gallon wide-mouth bottles, 
with bayonet-type metal closures, and widely used for fruit juices. 
Container 22 rests in and is supported by the inwardly dished top band 24 
of the stand indicated generally at 25. For convenience in carrying or in 
the field, stand 25 may be made foldable or collapsible, using well-known 
expedients for accomplishing such construction. Container 22 is provided 
with a removable closure 26 from which extends outlet tube 27 which is 
provided with a quick-opening valve 28. Outlet tube 27 extends down into 
and below the top of funnel 21 which has an outlet tube 30 provided with 
controlling means 31 that extends down to or just below the top of lower 
container 23. Funnel 21 may be ribbed or provided with other means for 
minimizing contact of the outer surface of the disposable filter medium 20 
with the inner surface of the funnel 21. 
It will be obvious that other suitable types of containers may be employed 
in place of those shown in the drawing for purposes of example. 
In practice, empty container 22 is filled not quite full with the water to 
be treated, leaving at least about a half inch air space below closure 26 
on filling. Closure 26 with the outlet tube 27 attached is tightened in 
place and then the container is inverted and put in place on stand 25. The 
apparatus is now ready fo use and the valve 28 is opened, allowing air to 
enter and pass upwardly into container 22. As a result, water begins to 
flow from container 22 into the filter funnel 21 and will rise in it until 
its level is above the bottom of outlet tube 27, thus shutting off the 
ingress of air into container 22 and stopping the flow of water from it. 
Flow of water through the filter element 20 may be regulated as desired by 
adjusting the valve 31. In most cases no restriction of flow is necessary 
beyond that provided by the filter medium itself. If, however, taste or 
chemical tests show that removal has not been complete, reducing the rate 
of flow may be indicated. An alternative procedure is to put the same 
water through the filter more than once. 
Ordinarily, the disposable filter medium 20 of my invention should not be 
used more than once or twice, and only on one day. To do otherwise can 
defeat a basic objective of the invention which is to prevent the 
self-contamination of the activated carbon previously mentioned. The low 
cost of the disposable filter medium 20 makes a single use of it entirely 
practical and economical. 
The filter system of my invention is designed specifically for removing 
objectionable tastes and odors and incidentally minute amounts of some 
types of organic and inorganic matter from drinking water. It is not 
designed to disinfect water contaminated with pathogenic bacteria or other 
organisms, and no claim or intimation of claim of disinfection is made. 
For emergency disinfection in the field, water suspected of being 
biologically contaminated may be disinfected in known manner by adding to 
the water an effective excess of chlorine in the form of sodium 
hypochorite from a commercial bleaching solution and, after a prescribed 
length of time, removing residual chlorine by means of the filter system 
of my invention; but this procedure of "super chlorination" and 
"dechlorination", as it is known in the water purification art, should be 
practiced only by a person with a thorough understanding of the procedure, 
with the knowledge and materials for making and interpreting the 
appropriate tests, and who will assume responsibility for the results. 
Nor is the filter system of my invention designed to clarify a turbid water 
or a highly colored one (the color being due most often to dissolved 
organic matter), although some degree of clarification and removal of 
color (and of some other organic and inorganic impurities) may be 
accomplished; generally speaking, neither a turbid water nor a highly 
colored one is suitable for drinking and must be given specific treatment 
to remove the turbidity or color as is done routinely in conventional 
filter plants.