Process and apparatus for removal of impurities from liquids

A unit is disclosed for removal of impurities present in liquids such as waste water effluent. The unit comprises a vessel containing a loose quantity of particulate treating material for absorption or reaction with the impurities in the liquid. A wall of the unit has multiple small openings therein, each of the openings filled with a finely-divided, compacted, particulate filter material such as diatomaceous earth which is retained in the openings by one or more layers of a woven inert material such as nylon or polyester having mesh openings sufficiently small to prevent passage of the particulate filter material therethrough. The woven material is secured over the outer surface of the openings in the wall of the vessel. Means are mounted within the vessel to progressively sweep over the inner surface of the wall just out of contact therewith and over the openings in which the particulate filter material is retained to remove impurities lodged thereon and prevent blinding of the filter material by such impurities. The same means also acts to uniformly mix the particulate treating material held within the vessel. The liquid with the impurities removed, because of the pressure differential between the inside and outside of the vessel, passes through the particulate filter material retained in the small openings of the vessel and is discharged from the housing surrounding the vessel. The treating material, once spent, is replaced as necessary.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a unit for removal of impurities from liquids and 
to a method for doing so. 
2. Description of the Prior Art 
Removal of impurities from liquids such as aqueous solutions, particularly, 
heavy metals present in small quantities in waste water effluent, is an 
acute problem due to the toxicity of the heavy metals and the increasingly 
stringent water quality regulations regulating discharge of such materials 
into water bodies. In many areas, water containing small quantities of 
heavy metals such as chromium, lead, mercury, cadmium, beryllium, etc. 
cannot be discharged into municipal sewage systems without removal of the 
heavy metals to an extremely low level. 
For other purposes, filtering of aqueous solutions is not adequate with 
conventional filtering devices because of the nature of the material to be 
filtered. For example, ferric hydroxide is a gelatinous solid which is 
very difficult to filter. Fruit juices containing impurities rendering the 
solution cloudy are also difficult to filter and clarify. 
Liquids such as used motor oils, tallow, etc. are difficult to purify by 
conventional means. 
The removal and recovery of hexavalent chromium from aqueous metal treating 
baths by contact of the hexavalent chromium with a lead compound to form a 
water-insoluble lead chromate is disclosed in U.S. Pat. No. 3,493,328. 
U.S. Pat. No. 3,791,520 also discloses a system for removing chromium 
anions present in small quantities from waste waters by contacting the 
waste water stream with a particulate carrier having a water insoluble 
lead compound adsorbed thereon, the lead compound reacting with the 
chromium in the waste water stream to form a water-insoluble lead 
chromate. The system for chromium removal disclosed in U.S. Pat. No. 
3,791,520 provides an effective method of chromium removal; however, the 
flow rate through the system must be closely controlled to prevent 
"channeling" which results in inadequate removal of the chromium anions 
from the incoming waste water stream. In an effort to overcome the 
problems encountered with the unit described in U.S. Pat. No. 3,791,520, 
the unit disclosed and claimed herein was designed. 
The use of chitin and chitosan to remove metal ions from aqueous solutions 
is known from U.S. Pat. Nos. 3,533,940 and 3,635,818. 
SUMMARY OF THE INVENTION 
It is a primary object of this invention to provide a unit for removal of 
impurities from liquids, the impurities generally present in small 
quantities, by contacting the liquid containing the impurities with a 
loose, particulate treating material which acts to remove the impurity 
from the liquid stream by reaction, by ion exchange or by adsorption, the 
treating material held in a vessel having a wall with multiple small 
openings therein, each filled with an inert, compact, finely-divided 
filter material retained therein. 
It is a further object of this invention to provide a unit for removal of 
metal ions present in small quantities in waste water streams by feeding 
the metal ions into a vessel having multiple small-sized openings in a 
wall thereof filled with an inert, particulate, finely-divided filter 
material retained in the openings of the vessel by a fine mesh material 
covering the outer surface of the wall and the openings, the vessel filled 
with a particulate treating material which removes the metal ions 
contained in the aqueous stream, the metal ions retained within the vessel 
while the water with the ions removed passes through the particulate 
filter material for discharge. 
It is a primary object of this invention to provide a unit for removal of 
impurities from non-aqueous liquids such as hydrocarbon oils, tallow, etc. 
by contacting the non-aqueous liquid containing the impurities with a 
loose, particulate treating material which acts to remove the impurity 
from the liquid, the treating material held in a vessel having a wall with 
multiple small openings therein, each filled with an inert, compact, 
finely-divided filter material retained therein. 
It is a further object of this invention to provide a unit for removal of 
impurities employing means within the treating vessel to progressively 
sweep the inner surface of the vessel over the openings therein to prevent 
blinding of the filter material retained in the openings by solids and to 
uniformly distribute the treating material within the vessel. 
It is a further object of this invention to provide a unit for removal of 
heavy metals present in small quantities from water streams by contact of 
the water stream containing the heavy metal with particulate, 
naturally-occurring polysaccharide polymer held within a cylindrical 
vessel having multiple small openings therein filled with a compact, 
inert, finely divided filter material. 
These and other objects are accomplished by a system which comprises (1) a 
vessel holding a charge of a particulate treating material which acts to 
remove impurities from the liquid fed therein, the vessel having multiple 
small openings in a wall thereof filled with a compact, inert, 
finely-divided filter material retained in the openings by suitable means, 
and (2) means for repeatedly and progressively sweeping the inner surface 
of the vessel over the openings therein and just out of contact with the 
inner vessel wall to prevent blinding of the particulate filter material 
retained in the openings, the same means also mixing and distributing the 
treating material within the vessel.

DETAILED DESCRIPTION OF THE INVENTION 
Aqueous streams containing heavy metal ions such as chromium, banium, lead, 
zinc found in waters in the plating industry can be treated with the unit 
disclosed to remove the metal ions to such a low level that there is no 
problem in discharging the resultant effluent into water bodies. 
The unit may be also used to remove ferric hydroxide, phosphates, and 
cyanide from aqueous streams, remove impurities from water discharged from 
leather tanneries, filter fruit juices or wines, filter waste petroleum 
oils, etc. 
FIG. 1 illustrates one system for removing impurities from liquids. An 
outer cylindrical housing 10 having end walls 16 and 18 is provided with a 
discharge port 12 for discharge of treated liquid after it passes into and 
through the openings in the wall of an inner cylindrical vessel 14. End 
walls 16 and 18 include shoulder portions 17 and 19 of substantially the 
same diameter as the inner diameter of shell 20 of the inner cylindrical 
vessel. The end walls 16 and 18 cap the open ends of vessel 14. O-ring 21 
provides an effective seal between wall 20 and the shoulder portion 17 of 
end wall 16. End wall 18 includes a flange portion 11 which is secured to 
an integral flange portion 13 of housing 10 by suitable fastening means 
15. O-ring 23 provides an effective seal between portion 13 and housing 
10. Cylindrical wall 20 is secured by suitable means over the flange 
portion 19 of end wall 18. End wall 19 has an inlet port 25 therein for 
introducing the liquid to be treated into the interior of vessel 14. The 
inlet port may be fitted with a pressure meter 27 and/or flow meter if 
desired. Cylindrical wall 20 has multiple small openings 22 therein (see 
FIG. 3). The size of the openings may vary but preferably range from 1/8 
to 1/2 inch in diameter. The outer housing 10, cylindrical vessel 20 and 
end walls 16 and 18 are preferably manufactured from a synthetic plastic 
material which can withstand highly acidic materials without damage 
thereto. The units may also be manufactured from stainless steel or other 
suitable metals if desired, depending on the water to be treated. 
Imbedded in each of the openings 22 is a finely-divided, particulate, 
inert, filter material 24, such as diatomaceous earth. The particle size 
of the filter material is chosen depending on the solids to be retained. 
The particle size of the filter material 24 should be sufficiently small 
to prevent passage therethrough of particulate solids in the waste water. 
A preferred particle size is on the order of 2 to 5 microns, on the 
average. Too small a particle size of filter material results in too slow 
filter rate while too large a particle size does not effectively remove 
the impurities sought to be removed. To retain the filter material within 
the openings 22, a woven fabric 23 or other suitable material having a 
mesh size small enough to prevent passage of the particulate filter 
material therethrough is placed over the outer surface of the cylindrical 
shell 20 and over the openings 22. For example, a woven nylon or polyester 
knit cloth adhesively bonded to the outer surface of the cylindrical shell 
has been found to work adequately. 
Mounted within the vessel are a series of blades 26 which extend 
substantially the length of the vessel. Each blade is secured by suitable 
struts 28 to a rotatable shaft 30 axially mounted in the vessel. The outer 
periphery of each of the blades is designed to pass over the inner 
openings as close as possible to the inner surface of the wall 20 without 
affecting the filter material 24 contained in the opening 22. The 
clearance between the blades and the inner surface of wall 20 is 
preferably about 1/64-inch. Shaft 30 extends through an opening in wall 18 
and is connected to suitable power means 32, such as a hydraulic motor by 
a connector 29 for rotation thereof. A standard shaft packing gland 31 
surrounds shaft 30 to prevent leakage through end wall 18. 
For removal of hexavalent chromium from waste water solutions the interior 
of vessel 14 may be filled with a water-insoluble lead compound which 
reacts with chromium anions in the water being treated to form 
water-insoluble lead chromate. The lead compound used may be lead oxide, 
lead carbonate, lead hydroxide, or other water-insoluble lead compound. 
The particle size of the particulate filter material 24 retained in the 
openings of the cylindrical shell 20 is chosen to prevent passage of the 
finely divided lead chromate precipitate which forms as a result of the 
reaction of the water-insoluble lead compound in the vessel with the 
chromium anions contained in the waste water stream. The smaller the 
particle size of filter material used, the lower the rate of filtration. A 
pressure differential between the interior and exterior of vessel 14 of 3 
to 6 psi is maintained for adequate filtration. It has also been found 
that a wall thickness of the cylindrical shell 20 should be from 1/4" to 
1/2" and preferably 3/8" for optimum results. The depth of the 
diatomaceous earth 24 filling the openings 22 in the cylindrical shell is 
equal to the wall thickness. The vessel is filled with the particulate 
lead compound in loose form or adsorbed in the pores of a particulate 
carrier such as disclosed in U.S. Pat. No 3,791,280. Waste water 
containing small quantities of chromium anions is fed into the vessel 
through inlet port 25. On contact with the lead compound in the 
cylindrical vessel, a finely-divided water-insoluble lead chromate 
precipitate is formed. The water passes through the diatomaceous earth 
filter material 24, (FW50 with a particle size of about 1/64-inch), the 
diatomaceous earth preventing passage of the lead chromate precipitate 
therethrough. The blades 26 within the vessel are rotated at a speed 
sufficient to prevent blinding of the diatomaceous earth filter material 
24 by the finely-divided lead chromate precipitate. The blades also 
continuously mix the lead compound within the vessel to prevent 
channeling. The water with the chromium removed is discharged from the 
housing 10 through port 12. If desired, monitoring means, such as a 
conductivity meter, may be used to continuously sample the discharge water 
to determine the level of chromium anions in the water being discharged. 
When the bed of lead within the vessel is substantially spent 
water-soluble chromium will pass through the filter material causing a 
change in the conductivity of the water being discharged. The monitor, if 
desired, can be connected to suitable control means to automatically 
discontinue feeding water into the unit or to notify an operator to take 
appropriate action. Two or more units can be run in tandem so that when 
one unit is spent the waste water to be treated can be fed into the 
adjacent unit. The lead chromate precipitate contained within the vessel 
can be recovered and sold as a pigment to the paint industry, or otherwise 
used. 
The system disclosed is also useful for removal of other heavy metals, such 
as nickel, cadmium, mercury and lead present in small quantities in water 
streams, using a particulate treating material containing a 
naturally-occurring polysaccharide polymer such as chitin or chitosan as 
disclosed in U.S. Pat. Nos. 3,533,940 and 3,635,818. Chitin is the main 
structural component of lobster, shrimp and crab shells as well as the 
exterior skeletons of other crustaceans, insects and spiders. Chitin is 
composed of chains of glucose units in which one hydroxyl in every glucose 
fragment is replaced by acetamido group. "Chitosan", a deacylated form of 
chitin produced by heating chitin in aqueous acid, has similar properties 
to chitin. Both chitin and "Chitosan" act as ion exchange materials for 
the removal of heavy metals such as chromium, lead, mercury, zinc and 
cadmium contained in water soluble form in water streams. The cylindrical 
vessel 14 is filled with particulate shrimp, lobster or crab shells or 
other source of chitin, the chitin or chitosan acting as an ion exchange 
material to remove the solubilized heavy metals in the water stream fed 
into the vessel. The pH of the entering stream to be treated is preferably 
adjusted to the pH of less than about 7, such as pH 6.5. The cylindrical 
vessel 14 is filled with the particulate chitin polymer. The particle size 
of the chitin or chitosan should range between 6 and 60 mesh (U.S. Sieve 
Series). As mentioned earlier the small openings in the vessel wall are 
filled with a compact, finely-divided, particulate filter material such as 
idatomaceous earth. Blades within the vessel are used to uniformly mix the 
particulate treating material contained therein to prevent channeling and 
to assure uniform action of the heavy metals contained in the water stream 
with the treating material. As mentioned previously, the water discharged 
from the unit can be continuously monitored to determine the effective 
removal of the heavy metals contained therein. When the ion exchange 
properties of the chitin or chitosan have been substantially spent, the 
incoming water to be treated can be transferred to a second unit. The 
heavy metals sequestered by the treating material in the cylindrical 
vessel can be recovered by pyrolysis of the material. Pyrolysis is a known 
technique involving the heating of the bed of treating material in a 
closed vessel in the absence of oxygent sufficient to decompose the 
treating material and recover the metal. 
One of the problems associated with the use of shrimp or crab shells is 
that they begin to smell very quickly after the meat is removed from the 
shells due to decay. This makes them almost impossible to use because of 
the odor associated therewith. It has been found that soaking the shells 
in a solution of 0.5 to 4 percent by weight formaldehyde prevents their 
decay. After soaking in formaldehyde the shells can be dried and used 
without any odor associated therewith. 
The addition of formaldehyde or other aldehyde to the treating material 
also has the advantage of destroying free and/or chemically combined 
cyanide present in the aqueous solution to be treated, as described in 
U.S. Pat. No. 3,505,217. 
If the aqueous stream to be treated contains gross amounts of heavy metals 
it is preferable to subject it to pretreatment to reduce the level of the 
heavy metals. For example, acid solutions such as pickle liquor solutions 
may be pretreated by adjusting the pH of the solution with caustic or 
other suitable base and preferably to around pH 6.5, and then adding 
sodium sulfide to precipitate out the heavy metal. 
The unit may also be used in conjunction with chitin or chitosan to remove 
cyanide present in aqueous streams. For example, in a solution containing 
caustic and nickel cyanide, an aldehyde such as formaldehyde or 
acetaldehyde is added which reacts with and breaks down the cyanide. The 
pH of the solution is then preferably adjusted to around pH 6.5 and sodium 
sulfide added to precipitate out the heavy metal which is retained within 
the filter unit by the filter material 24. 
The unit may also be used in conjunction with conventional filter aids 
(diatomaceous earth) as the treating material to filter and clarify fruit 
juices such as apple juice and wines. A coarser grade of diatomaceous 
earth is used for the treating material than for the filter material 24. 
For cleaning crankcase oil the unit may be filled with an acid clay as the 
treating material.