Water filter abstract
A drinking water filter for removing lead at point-of-use composed
of specially treated gamma alumina particles between 48 and 100
mesh (0.148-0.297 mm), gamma alumina neutral (about 7 surface pH)
or basic (about 9 surface pH) is washed in highly purified H.sub.2
O at 100.degree. C. to reduce alumina surface pH to 3.5-5.0 and
then washed with highly purified H.sub.2 O at ambient temperature.
The alumina is placed for three to twelve hours in bath having equivalent
pH value (3.5-5.0) of acid electrolyte, diluted with a highly purified
H.sub.2 O, preferably HCl, ascorbic acid or EDTA, adjusted to alumina
surface pH level and desired degree of dilution by salts such as
NaCl and/or alkalies such as NaOH to transfer to adsorbent surface
materials that effect selective ion exchange with lead and other
heavy metal ions or otherwise cause their removal from drinking
water. Upon removal of alumina from bath, it is vacuum washed and
then dried in an oven at 200.degree. C. to 350.degree. C. for about
two hours. For wet packing in cartridges about 50%, and for dry
packing about 98%, of moisture is so removed. Cartridges contain
about 200 grams alumina for each one-half gallon capacity flow per
minute, the treated alumina being tightly packed in the cartridges
to prevent channeling while not causing a pressure drop at maximum
rated capacity of more than about 10 psi across the cartridge.
Water filter claims
Having disclosed my invention, what I claim as new and to be covered
by Letters Patent of the United States is:
1. A process for removing lead and other heavy metals from drinking
water which is discharged from a drinking water facility comprising
filtering said water prior to its discharge from said facility by
directing it to flow through a filtration media of gamma alumina
that has an effective surface pH of substantially 3.5 to 5.0 and
wherein there is sufficient contacting by said drinking water of
said alumina's surface to remove lead and other heavy metals from
the drinking water while the water is flowing through said filtration
media so that the lead content of the drinking water, as discharged
from said facility, is less than about five micrograms per liter.
2. A process in accordance with claim 1 wherein the mass of said
gamma alumina filtration media is in the range of 200 to 1000 grams
and the maximum flow rates of said drinking water discharged from
said facility in said process being in proportion to the amount
of said gamma alumina filtration media in the range of one-half
to three gallons per minute.
3. A process in accordance with claim 2 wherein said filtration
media is packed in a cartridge through which said drinking water
flows at a rate so that the pressure reduction across said cartridge
is not more than about ten pounds per square inch.
4. A process in accordance with claim 1 wherein said gamma alumina's
effective adsorbent surface pH is less than the pH of the water
5. A process in accordance with claim 1 wherein said filtration
media is in the form of particles which are of a size in a range
of 48 to 100 mesh.
6. A process in accordance with claim 5 wherein said particles
are of a size which is in a range of 60 to 80 mesh.
7. A process in accordance with claim 1 wherein the lead content
of said drinking water is in an amount of up to about 350 parts
per billion before it is received by said filtration media, and
said filtration media reduces said lead content by removing approximately
99% of said lead content from said drinking water by said drinking
water contacting said filtration media as it flows therethrough
and without said filtration media causing a reduction of more than
about ten pounds per square inch effective pressure of said drinking
water at said discharge from said facility.
8. A process in accordance with claim 1 wherein the pH of said
drinking water is in a range of 6.5 to 10.
9. A process for the removal of heavy metals from dilute aqueous
solutions thereof containing one or more of said heavy metals as
well as competing ions selected from the group consisting of calcium,
magnesium and mixtures thereof, which comprises contacting said
aqueous solution with a filtration media composed of an adsorbent
of a crystalline structure, having a physio-chemical effective surface
and pore texture wherein the pH of said effective surface is substantially
3.5 to 5.0 until said heavy metals are essentially entirely removed
from said aqueous solution.
10. A process in accordance with claim 9 wherein said heavy metals
include lead and said aqueous solution consists of drinking water
which contains up to 350 parts per million of lead in solution and
has a pH in a range of 6.5 to 10.
11. A process in accordance with claim 9 wherein said heavy metals
include lead, copper and zinc.
12. A process in accordance with claim 9 wherein said aqueous
solution is drinking water which contains up to 350 parts per billion,
and wherein substantially 99% of said lead content is removed by
said effective surface from said drinking water.
13. A process in accordance with claim 12 wherein said crystalline
adsorbent consists essentially of gamma alumina.
14. A process in accordance with claim 13 wherein said gamma alumina
consists essentially of particles having a particle size in a range
of 48to 100 mesh.
15. A process in accordance with claim 13 wherein said gamma alumina
consists essentially of particles having a particle size of 60 to
16. A process in accordance with claim 13 wherein said gamma alumina
is contained within a tightly packed cartridge containing 200 to
1000 grams of such gamma alumina, said drinking water flowing through
said cartridge at a rate in the range of about one-half to three
gallons per minute and the reduction in line pressure across said
cartridge caused by said filtration media therein being not more
than ten pounds per square inch.
17. The process of claim 9 wherein said crystalline adsorbent
is selected from the group consisting of alumina, carbon, silica
gel and zeolites.
Water filter descriptionFIELD OF THE INVENTION
The invention relates to a filter for the removal of lead and other
heavy metals from drinking water at its point-of-use and the method
of manufacturing the filtration media and units. More particularly,
the invention is directed to the use of a specially treated alumina
for the removal of lead and other heavy metals from drinking water
and to the preparation and packaging of the alumina into filters
to maximize the removal of lead and other heavy metals dissolved
in the metal rapidly and efficiently.
BACKGROUND OF THE INVENTION
Low levels of lead, previously considered safe, have been found
to cause high blood pressure and strokes in adults and to adversely
affect the development, mental abilities and hearing of children.
Most of the lead in water that is consumed originates from corrosion
in water-delivery systems and home plumbing. Drinking water delivered
from municipal and other water suppliers is not normally high in
lead content. Thus, the primary source of lead is derived from subsequent
corrosion of service connections, pipes, fixtures and other plumbing
parts of systems which distribute water to end consumers. Much of
this lead-bearing plumbing is privately owned, that is, it is installed
permanently within homes and buildings. Because of this, as a practical
matter, the reduction of lead in drinking water has been accomplished
primarily by introducing into the drinking water corrosion inhibitors,
by adjusting the alkalinity level of the water by raising its pH
value to eight, by service connection replacements of water distribution
systems to homes or buildings, and by public education concerning
the danger of lead in drinking water. Substantial levels of lead
have also been found in water delivered to drinking fountains such
as those installed in office buildings, schools and other public
The replacement of plumbing in a home or other building is seldom
a practical solution to achieve the desired reduction of lead and
other heavy metals in drinking water at point-of-use.
Purification of water at point-of-use is a more logical solution
to the problem. Conventional technologies which can be used for
this purpose include reverse osmosis, distillation, and filtration
utilizing activated carbon and ion-exchange resins. Reverse osmosis
and activated carbon filtration units have been widely employed
for home drinking water treatment to remove a variety of contaminants,
primarily organics from drinking water. These filtration units can
also remove lead. Further, distillation and ion-exchange resin units
are also effective in removing lead from drinking water. These technologies,
however, are non-specific in that they are not directed primarily
to the removal of lead and other heavy metals, and for this reason
their lead-removal capacities for drinking water are significantly
less than might otherwise be the case. The situation is aggravated
if alkalinity of the water is increased or corrosion inhibitors
are added, which are frequent methods utilized by water treatment
plants to reduce the corrosivity of their treated water. Current
systems of reverse osmosis do not work well using line pressures
which exist in most homes. In addition, their capacities to produce
purified water are relatively low. A high pressure pump needs to
be added which may prove expensive and impractical. Single-stage
distillation units are quite energy intensive and, for this reason,
generally should be avoided. Thus, most known technologies for reducing
lead and other heavy metals in drinking water at point-of-use are
either capital intensive or costly to operate, or both.
The use of alumina for water filters is known. In addition, gamma
alumina is known to be selective for heavy metals. Unfortunately,
the prior art experience with alumina has not demonstrated that
this filtration substance to be a satisfactory solution for point-of-use
filtration of drinking water at most locations from the standpoints
of efficiency and capacity.
The following is a list of literature and other publications which
reflect the skill of the art and, for such purposes, are incorporated
herein by reference:
1. Lippens, B. C. and Steggerda, J. J. (1970) Active Alumina. In
Physical and Chemical Aspects of Adsorbents and Catalysts (B. G.
Linsen, Ed.). Academic Press, New York, N.Y.
2. Srivastave, S. K. et al. (1988) Studies on the Removal of Some
Toxic Metal Ions from Aqueous Solutions and Industrial Waste. Part
I (Removal of Lead and Cadmium by Hydrous Iron and Aluminum Oxide).
Environ. Tech. Letters 9 1173-1185.
3. Hohl, H. and Stumm, W. (1976) Interaction of PB.sup.2+ with
Hydrous.alpha.-Al.sub.2 O.sub.3. J. Colloid Interface Sci. 55 281-288.
4. Huang, C. P. et al. (1986) Chemical Interactions Between Heavy
Metal Ions and Hydrous Solids. In Metal Spectation, Separation,
and Recovery (J. W. Patterson and R. Passino, Eds.). Lewis Scientific
Publishing, Comp., New York, N.Y.
5. Bilinski, H. et al. (1975) Copper and Lead in Natural Water.
Vom Wasser 43 107-116.
6. Murray, J. and Brewer, P. G. (1977) Mechanisms of Removal of
Manganese, Iron and Other Trace Metals from Sea Water. In Marine
Manganese Deposits (G. P. Glasby, Ed.) Elsevier Scientific Publishing
Company, New York, N.Y.
7. Grahame, D. G. (1955) Electrical Double Layer. J. Chem. Physic.
8. Levine, S. and Smith, A. L. (1971) Theory of Differential Capacity
of the Oxide-Aqueous Electrolyte Interface. Dis. Fara. Soc. 52
9. Matijevic, E. et al. (1960) Detection of Metal Ion Hydrolysis
by Coagulation: II. Thorium. J. Phy. Chem. 64 1157-1161.
10. Matijevic, E. et al. (1966) Stabilization of Lyophobic Colloids
by hydrolyzed Metal Ions. Faraday Soc. 42 187-196.
11. James, R. O. and Healy, T. W. (1972) Adsorption of Hydrolyzable
Metal Ions at the Oxide-Water Interface. Parts I, II and III. J.
Colloid & Interface Sci. 40 42-81.
12. Stanton, J. and Maatman, R. W. (1963) The Reaction Between
Aqueous Uranyl Ion and the Surface of Silica Gel. J. Colloid Sci.
13. Dugger, D. L. et al. (1964) The Exchange of Twenty Metal Ions
with the Weakly Acidic Silanol Group of Silica Gel. J. Phys. Chem.
14. Huang, C. P. and Stumm, W. (1973) Specific Adsorption of Cations
on Hydrous.alpha.-Al.sub.2 O.sub.3. J. Colloid & Interface Sci.
15. Stumm, W. et al. (1970) Specific Chemical Interaction Affecting
the Stability of Dispersed Systems. Croatica Chem. Act 42 223-228.
16. Baes, C. F. and Mesmer, R. E. (1976) The Hydrolysis of Cations.
John Wiley & Sons, Inc., New York, N.Y.
17. Farley, K. J. et al. (1985) A Surface Precipitation Model for
the Sorption of Cations on Metal Oxides. J. Colloid & Interface
Sci. 106 226-242.
18. Elliott, H. A. and Huang, C. P. (1984) Factors Affecting the
Adsorption of Complexed Heavy Metals on Hydrous-Al.sub.2 O.sub.3.
Wat. Sci. Tech. 17 1017-1028.
19. Kummert, R. and Stumm, W. (1980) The Surface Complexation of
Organic Acids on Hydrous.alpha.-Al.sub.2 O.sub.3. J. Colloid &
Interface Sci. 75 373-385.
20. Kim, J. S. (1988) Characteristics of Humic Substances and Their
Removal Behavior in Water Treatment. Ph.D. Dissertation, Georgia
Institute of Technology, Atlanta, Ga.
21. Chian, E. S. K. et al. (1987) Comparison of High Molecular
Weigh Organic Compounds Isolated from Drinking Water in Five Cities.
In Organic Pollutants in Water, Advances in Chemistry Series 214
American Chemical Society, Washington, D.C.
22. APHA-AWWA-WPCF (1985) Standard Methods for the Examination
of Water and Wastewater, 16th edition. American Public Health Association,
23. The Environmental Chemistry of Aluminum, (1989) CRC Press,
Inc. Boca Raton, Fla.
24. Principles of Electroplating and Electroforming, W. Blum and
G. Hogaboom, 1st Ed., Chapter XVII, McGraw-Hill Book Company, Inc.,
New York, N.Y.
SUMMARY OF THE INVENTION
Pure alumina is commercially prepared by various processes. In
one, the bauxite is treated under pressure with a hot solution of
caustic soda to form sodium aluminate and goes into solution while
the impurities remain behind as the residue known as "red mud."
Pure aluminum trihydrate is precipitated from the solution by heating
The hydrated aluminum oxide occurs in a variety of forms, such
as the trihydrate (Al.sub.2 O.sub.3.3H.sub.2 O or Al(OH).sub.3)
and monohydrate. Common forms of the aluminum trihydrate are gibbsite,
bayerite and nordstandite. Common forms of the aluminum monohydrate
are diaspore and boehmite. The structure and morphology of the raw
materials that occur as aluminum hydroxides, are of particular importance
for determining the physical characteristics of the resulting aluminas,
including their specific adsorption properties. This relates to
both the alumina's physical structure and its purity inasmuch as
the raw materials may contain impurities, such as alkali oxide,
iron oxide and sulfates.
If the trihydrate is heated to a temperature that does not exceed
600.degree. C., what is known as a low-temperature alumina is produced,
Al.sub.2 O.sub.3.nH.sub.2 O, wherein 0<n<0.6. Gamma aluminas
which are almost entirely anhydrous Al.sub.2 O.sub.3 are obtained
by heating the trihydrates to temperatures of between 900.degree.
C. and 1100.degree. C. Upon dehydration of the aluminum hydroxides
at increasing temperatures, two neighboring --OH combined to produce
H.sub.2 O and provide an oxygen ion on the adsorbent surface which
is described as a strained oxygen bridge.
At low temperatures, wherein up to one-third of the alumina adsorbent
surface is covered with --OH ions, adjacent --OH ions are randomly
removed without disturbing the local order otherwise. However, the
oxygen ions on the surface are isolated in the sense that none of
the oxide ions is on a site adjacent to another oxide ion. Upon
further hydration by heating, a vacancy disorder occurs and the
remaining --OH ions now have from zero to four oxide neighbors.
At still higher temperatures, a migration of surface ions takes
place and there is a gradual loss of surface area. The disposition
of the --OH ions are also affected by reagents which may be used
during the dehydration process.
By providing the proper physio-chemical properties of aluminas
in terms of crystallinity, pore size and texture and the chemical
nature of the adsorbent surface, which depends on thermal-chemical
dehydration processes and the selected raw material, considering
its trace impurities and optimum ratio of surface oxide-hydroxide
ions, an alumina filtration material can be produced which has an
increased selectivity for the adsorption of soluble lead and lead
High purity alumina is commercially available in beta and gamma
forms. For each of these forms it is available in accordance with
its pH value as neutral or basic or a mixture of neutral and basic.
Depending upon the raw material, the neutral gamma alumina will
have a pH of around 7 including somewhat less than 7 and thus be
acidic. The surface pH of the basic gamma alumina is about 9. For
the purpose of the instant invention, the gamma forms are preferred,
having pH ranges, as described above, in the neutral or basic ranges.
Particular attention must be paid to the crystalline characteristics
of the alumina as received. The structure and morphology of the
alumina are most important. This includes the crystalline structure,
pore texture and the chemical characteristics of the adsorbent surface.
Generally, the crystalline structure and pore texture should be
such as to maximize the adsorption qualities of the alumina. Subsequent
heat treatment for thermal dehydration and activation of the alumina
is to be avoided in the method in accordance with the invention
because it has been found to desensitize the alumina surface for
the selective filtration of lead and other heavy metals.
Another quality of the alumina which has been found to contribute
substantially to its overall performance in the adsorption of lead
from drinking water is its particle size, which should be from 48
to 100 mesh and preferably 60 to 80 mesh. If the mesh size is larger,
channeling is more likely to occur. If smaller, it requires undue
pressure for water to traverse the filter media.
Another important aspect of the invention is the effective removal
of impurities from the alumina such as alkali oxide, iron oxides
and sulfates, as well as other minerals, the presence of which can
adversely affect the specific adsorptive properties of the alumina.
The method of the invention includes the washing of same with deionized
and distilled water, and treatment of the media with highly diluted
water with a halogen, preferably a chloride or electrolyte solution.
In particular, the water used for these purposes should be lead
free, preferably to the extent that less than one microgram per
liter, or one part per billion, of lead remains in the water after
filtration. Water filtered first by reverse osmosis and then in
accordance with the invention has been used with satisfactory results
and all water used in the inventive method was first so processed.
In the method in accordance with the invention, the aluminum oxide,
type basic and/or neutral, size 48-100 mesh, is first washed with
the highly purified water at or about 100.degree. C. to reduce the
alumina's alkalinity to a low pH surface level of about 3.5 to 5.0
preferably nearer to 3.5. When the alkalinity has been reduced to
this level, the alumina is further washed for at least several minutes
with the highly purified water. The alumina is then treated by retention
in a water tank at ambient temperature, wherein hydrochloric acid
or other electrolyte solution diluted by about a 1 in 100 ratio
wherein the alumina is retained in the diluted halogen electrolyte
solution bath for approximately three to twelve hours. The washing
process is completed by a vacuum wash with the highly purified water.
Other solutions which have been used successfully with the invention
include ascorbic acid, which is mixed with the salt, NaCl and has
its pH value adjusted from 1 to about 5 by the addition of NaOH.
Another acid which can be used is EDTA, that is ethylenedianianetetraacetic
acid. Various other solutions known to react with lead as an electrolyte
may be used, particularly those which include a halogen such as
chlorine as a constituent.
The vacuum washing process is accomplished by placing the media
on a screen which may be stainless steel or polypropylene and subjecting
it to a substantial vacuum for removal of the water. The vacuum
pump has a capacity of 300 cubic feet per minute.
Next, the alumina is dried in an oven at temperatures of 200.degree.
C. to not exceeding 350.degree. C., for approximately two hours
until a desired portion of the water has been expelled from the
For a subsequent wet packing of the filtration cartridges, approximately
50% of the water is removed. For dry packing, approximately 98%
or more of the water is removed by this method.
Finally, the alumina, so treated, is tightly packed either by a
wet pack or for dry alumina by vibration to prevent channeling and
placed in containers known as cartridges to be used in the water
systems at point-of-use.
The filtration media in the cartridges, as packed, may be considered
as a chromatographic column in the sense that it adsorbs selected
media as it passes through the cartridge. An equivalent packed column
can be made by utilizing 100-300 mesh alumina particles which are
interconnected by polyethylene bonding so that each particle is
exposed to liquid traversing the cartridge and, at the same time,
the pressure across the cartridge at maximum flow rate is not more
than about 10 pounds per square inch.
Alumina filters prepared in accordance with the invention are extremely
selective to lead and other heavy metals, and performance is not
adversely affected by anions present in drinking water, such as
calcium, magnesium, nitrates and other chemicals. The invention
works well at all pH levels normal to drinking water. Filters are
generally designed for one year of use with flow rates up to three
gallons per minute. However, flow rates of the filters are essentially
limited only by the size and weight which can be tolerated in the
system at point-of-use and successful filters have been tested having
a flow rate of ten gallons per minute, such filters having been
prepared in accordance with the invention. The alumina media in
the filtration unit is capable of removing dissolved lead in drinking
water from approximately 350 parts per billion to 1 part per billion,
at normal flow rates and without an undue reduction in the effective
pressure at the point-of-use. The highest concentration of lead
in drinking water occurs in the first draw of water, usually in
the morning within the first two minutes of the draw. Filtration
units prepared in accordance with the invention quickly and efficiently
remove approximately 99% of the lead that occurs at this time and
subsequently, from the water which flows at point-of-use.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A high purity aluminum oxide, type basic or neutral, having a mesh
size of 48-100 (Tyler Standard Screen Scale) and preferably 60-80
is provided as the starting substance. Having particle sizes strictly
within the 48-100 mesh limits is important and is obtained by a
pneumatic separation process. In addition, high purity water is
produced which is used in all subsequent liquid treatment steps.
This water has been treated by a reverse osmosis process and further
filtration by filters in accordance with the invention so that its
impurities, if any, are virtually unmeasurable by existing analytical
equipment in common use. Its lead content has been reduced to less
than about one microgram per liter or, as used herein, one part
The starting aluminum oxide is then washed by the high purity water,
which has been heated to 100.degree. C., to reduce the alumina's
alkalinity to a low pH surface value of about 3.5 to 5.0. When the
appropriate low level of pH surface value is reached, the alumina
is further washed with the highly purified water for several minutes.
Although the pH surface values of 3.5 to 5.0 as used herein are
considered accurate analyses of the actual pH values, a standard
test wherein twenty grams of the alumina are stirred into a beaker
having fifty milliliters of deionized water, which is then analyzed
for pH, has consistently reflected higher pH levels by providing
analyses of 4.0 to 6.5. Therefore, whenever pH surface values of
about 3.5 to 5.0 are recited herein (values which are considered
by the inventor to be accurate), it should be appreciated that these
values may appear higher as a result of the particular type of analyses
employed, which for example, may reflect 4.0 to 6.5 pH. These latter
results should be considered equivalents which do not change the
scope of the invention.
The alumina is next placed in a water tank or bath with hydrochloric
acid or other electrolyte solution, wherein the ratio to water to
concentrated hydrochloric acid is about 100 to 1. Here, the alumina
is retained for three to twelve hours and then removed. The purpose
of this step is to transfer to the adsorbent surface substances
which will effect an ion exchange with lead and other heavy metals
passing through the filter as ions or otherwise will selectively
remove the lead from the water flowing through the cartridge. To
achieve this, the pH value of the diluted hydrochloric acid or other
electrolyte solution should be about the same as the pH surface
value of the alumina being treated. This pH value can be reached
by the adding, as appropriate, other materials to the solution which
makes up the bath. For example, when ascorbic acid is being used,
NaCl, and a small amount of NaOH can be added to adjust the pH level.
Although in all cases the acid is highly diluted, the dilutions
are not always 100 to 1. For the most favorable results, testing
is required to determine the best mix of constituents and dilution.
This is accomplished by conducting kinetic ion analyses which provide
analyses of the lead ion transfer to the adsorbent surface. In general,
materials should be used which will not add unacceptable toxicity
to the drinking water. With this limitation, other acids and salts
containing different halogens, for example, may be employed. The
important object is to provide on the adsorbent surface substances
which will remove lead ions and those of other heavy metals commencing
immediately as water flows through the cartridge and continuing
to do so for a reasonable period of time such as one year without,
at the same time, adding to the toxicity of the drinking water.
Next, the alumina is washed in a vacuum system with distilled filtered
water and, thereafter, the alumina is dried in an oven at a temperature
of about 200.degree. C. and, in any event, not above 350.degree.
C. for approximately two hours until 98% of the water has been removed.
Finally, the alumina is tightly packed in wet condition under pressure
(100-200 psi) or by vibration into filter cartridges which are elongated
cylinders of different sizes that, in practice, range from about
two inches in diameter and ten inches in length, to four inches
in diameter and twelve inches in length. Plumbing connections at
opposite ends for 1/4 inch up to 11/2 inch pipe sizes are provided.
The filters are designed to reduce lead levels in water from 350
parts per billion to 5 or less parts per billion, at 100%-90% efficiency
for a period in excess of one year.
Preferably the starting material is a mixed blend of high purity
alumina, basic and aluminum oxide neutral. The pH of the filtration
media is reduced to 3.5 to 5 and impurities are removed by the steps
recited above. A crystalline structure, having a physio-chemical
effective surface and pore texture results wherein in combination
with the particle size and the tightly packed nature of the media
in the filtration units provides very sensitive filtration of lead
and other heavy metals for drinking water at the point-of-use. The
media is capable of removing dissolved lead in drinking water so
that a reduction of approximately 350 parts per billion to 1 part
per billion occurs in one pass. By creating a low pH value, lead
ions are attracted to the alumina's adsorbent surface, irrespective
of expected pH levels of the water that is being filtered, assuming
that it is in a pH range of 6.5 to 10 as normally found in drinking
In contrast, alumina that has not been purified or treated by a
process, such as exemplified by the instant invention, removes lead
only at fifty percent efficiency. This is considered to be due primarily
to such alumina's alkali and unstable adsorbent surface. Aluminum
oxide which has not been purified generally has a surface pH value
of 10 to 14 and this, in turn, causes the pH in the water being
filtered to become unstable due to its high alkalinity and high
soda content. The filtration media is highly selective to lead and
other heavy metals, and its filtration performance is unaffected
by other ions which may be present in the drinking water such as
calcium, magnesium, nitrates and other chemicals. Accordingly, not
only lead, but also copper, zinc and other heavy metals are continuously
and simultaneously removed from the drinking water.
The alumina used in the invention is safe to the extent that it
will not leach more than 50 parts per billion of alumina in the
most adverse water conditions wherein there is a very low pH level.
Filters constructed in accordance with the invention have efficiently
reduced lead in drinking water in a wide range of temperatures (34.degree.-120.degree.
F.) without the efficiency of the lead removal or the water flow
being adversely affected.
The rate at which lead is removed is dependent on the contact time
of the water containing the lead with the media.
The inventor has found that some lead formation in water appears
as a result of radon gas in water in an unstable form. Units in
accordance with the invention remove lead efficiently even in the
presence of radon.
Evaluations of the invention using EPA Method 239.2 and also in
NSF Standard 53 have confirmed that lead is consistently removed
from drinking water at point-of-use by the invention to levels at
about or below 5 parts per billion.
The same process has been used by the inventor or, in theory, may
be used to prepare other adsorbents as filtration media such as
activated carbon, silica gel and various zeolites. In tests conducted
with adsorbents other than alumina wherein, in particular, the adsorbent
surfaces were treated as taught by the instant invention, roughly
the same level of removal of lead and other heavy metals resulted
except that the lifetime of such filters proved to be substantially
less. For example, a filter of activated carbon prepared in accordance
with the invention had a lifetime which is only about twenty percent
of that obtained in using gamma alumina.
The cartridges are loaded with approximately 200 to 1000 grams
of alumina according to the desired flow rate through the cartridge
which, at point-of-use, is typically from one-half to three gallons
per minute with a reduction in line pressure of not more than 10
pounds per square inch when a flow rate through the cartridge is
at the rate of capacity. Thus, there may be a reduction of the flow
rate from say, 40 pounds per square inch to 30 pounds per square
inch, in a typical home or office.
There are two types of packing used with the invention. One is
an extrusion method against a pressure of about 200 pounds per square
inch which is used for wet packing wherein only about 50% of the
moisture has been removed in the drying process. The pressure, which
should be at least 100 pounds per square inch and preferably 200
pounds per square inch in this process of loading the cartridges
should, in any event, be sufficient to prevent the formation of
channels through the filtration media whereby much of the media
will not be bypassed by the water flow and, at the same time, not
so much pressure as to cause a blockage. As indicated above, the
desired pressure reduction of water flowing through the cartridge
at capacity is about 10 pounds per square inch.
Another packing method is used wherein about 98% of the moisture
has been removed from the alumina in the drying process which is
termed a dry pack and is accomplished by vibrating the cartridge
at a rate of 3900 vibrations per second. The result is a densely
packed cartridge wherein channeling of the water through the cartridge
does not occur and, again, the pressure reduction caused by the
cartridge is not greater than about 10 pounds per square inch. Equipment
for the vibration is obtained from Alpine Pneumatics.
The foregoing description has been given for clearness of understanding
and unnecessary limitations should not be understood therefrom.
Modifications and further details will be obvious to those skilled
in the art.