|Title of Invention||
METHOD AND DEVICE FOR REMOVING CONTAMINANT TRACE SPECIES, ESPECIALLY ARSENIC, FROM WATER
|Abstract||A method and a device for purifying water from contaminant trace species, especially arsenic, by co-precipitating trace species during oxidation and precipitation of iron compounds with subsequent separation. The co-precipitation is improved by contacting the water with an iron-containing material prior to oxidation to increase the iron content of the water. Arsenic and other trace species harmful to health may be removed from water effectively and in a simple manner, thus being able to comply with the more restrictive limits of arsenic in drinking water.|
Title: Method and device for removing contaminant trace species, especially arse-
nic, from water
The present invention relates to a method and a device for purifying water from contami-
nant trace species, especially arsenic, by treating said water with iron and co-precipitating
trace species during oxidation and precipitation of iron compounds with subsequent sepa-
The presence of substances harmful to the environment or health in drinking water, even
in very small amounts (so called trace species), has become a focus of attention for indi-
viduals as well as authorities, as knowledge and analytical techniques improve. Arsenic
(As) in drinking water, for example, increases the cancer risk of human beings. Therefore,
authorities have lowered the limit for As in drinking water from 50 ug/l to 5 ug/l. However,
this resulted in a large number of waterworks failing to comply with a limit of 5 u.g/1 using
existing methods, and hence had either to close down or to invest in expensive purifica-
tion equipment. To this day, no profitable methods for this purpose are known capable of
reducing the content of arsenic from a frequently encountered level of 20-35 u.g/1 down to
below 5 jig/I. The problem is particularly pronounced in waterworks having groundwater
with a low iron content.
In waterworks with groundwater having a high content of iron compounds, the problem is
less pronounced, since arsenic is co-precipitated with oxidized iron compounds, when the
water is treated in a conventional way by oxidation, typically aeration, until iron precipi-
tates in sand filters or precipitation basins. However, it is not possible to remove arsenic
by conventional oxidation of water, if the iron content of the water is not sufficient to en-
sure the desired co-precipitation of present arsenic and other contaminants, including pes-
DE 197 45 664 A1 discloses a method for treating arsenic-containing water, where the
water flows through a reactor filled with an iron-containing granulate, said granulate being
produced by mixing sand and iron powder and subsequent firing under exclusion of oxy-
gen. In the reactor, the iron is oxidized by the oxygen dissolved in water generating Fe(lll)
ions, said ions together with As forming poorly soluble iron arsenate Excess Fe(lll) ions
are precipitated as iron hydroxide binding As by adsorption. Thus, As binds to the granu-
late, wherefrom it has to be removed at suitable intervals. When precipitating Fe(lll) com-
pounds, the granulate used agglomerates comparatively quickly and has to be exchanged
frequently. The manufacture of the granulate requires work and energy. Moreover, the
method requires the supply of additional oxygen to the reactor prior to treatment, if the
treated groundwater is low in oxygen. In conclusion, the known method is work-intensive,
complicated and expensive-
US 5 951 869 describes a reactor, where water is treated with iron while simultaneously
supplying oxygen. The treatment takes place in a fluid bed with iron particles as the
source of iron. The use of a fluid bed is a high-cost and complicated method.
EP 0 737 650 A2 and US 5 368 703 provide the enrichment of water with iron using an
electrolytic method. The use of electrolysis is energy-intensive and complicated.
My ref: PA 82125
1 February 2007
New page 2a
to be incorporated on page 2 after line 16
WO 98/57893 (Nikolaidis) discloses the treatment of arsenic containing water with metallic
iron under anaerobic conditions. The arsenic compounds are reduced and the iron is oxi-
dised providing iron ions leading to co-precipitation of arsenic compounds, but siili under
US 5 358 643 (McClintock) discloses treatment of arsenic contaminated water with an iron
salt, an acid and an oxidant until the water contains more iron than arsenic and has a posi-
tive oxygen/reduction potential (ORP) of about plus 600 mV ensuring that the arsenic will
be pentavalent (step a). Then the water is made basic (step b) and the formed reaction mix-
ture is reacted to precipitate compounds of As and Fe (step c) followed by separation of the
precipitates from the water (step d). The steps a and b, and in a preferred embodiment also
step c, are carried out without exposing the water/reaction mixture to air. Thus, an inten-
tional active oxidation during the co-precipitation of As and Fe is not disclosed.
US 2002/003116 A1 (Golden) discloses treatment of arsenic containing water first with an
oxidant (hydrogen peroxide) and thereafter with an iron salt (ferric sulfate).
JP 2003 126874 A (Hitachi) teaches to feed the water to be treated to an oxidizing vessel
where the water is aerated with an aerating means.
The above-mentioned methods have the common feature that the iron treatment takes
place concomitant with aeration or requires that the water has a suitable oxygen content
from the very start Accordingly, there is an increased risk that the system is clogged by
the precipitated oxidized iron compounds.
Hence, there is still a need for an uncomplicated and profitable method for removing arse-
nic and other trace species harmful to health from drinking water, especially drinking water
based on low-iron groundwater.
Disclosure of Invention
It has been found that arsenic, optionally residual pesticides and other trace species
harmful to health, are removable from water, especially drinking water, in a considerably
less complicated and at the same time more efficient manner, if the water to be treated is
first enriched with iron, while the oxygen content of the water is comparatively low, and
subsequently exposed to strong aeration.
Accordingly, the present invention relates to a method for purifying water from contami-
nant trace species, especially arsenic, by treating said water with iron and co-precipitating
trace species during oxidation, and precipitation of iron compounds with subsequent sepa-
ration, characterized in that
- first, the water is contacted with an iron-containing material for enriching the wa-
ter with iron compounds,
- then, the iron-enriched-water oxidizes for co-precipitation of the contaminant
trace species together with oxidized iron compounds, and
- finally, the precipitated compounds are separated from the water.
The iron compounds may be added to the water in a simple and reliable manner at ac-
ceptable cost by contacting the water with an iron-containing material, preferably iron ore
or metallic iron, particularly iron filings or swarfs, available as an inexpensive waste prod-
uct in the form of calcinated waste iron from cutting machines. This may be accomplished
by leading the water through a bed of iron ore, iron particles, iron filings or swarfs or any
other natural iron-containing material having a large surface. The water may be distributed
across the bed, e. g. by naturally spraying the bed, and after treatment, it may be removed
from the bottom of the bed by means of suitable openings.
Next, the iron-treated water is led to a conventional aerator and, if necessary, a suitable
filter, e. g. a sand filter, to remove arsenic and other trace species. This treatment is car-
ried out in a conventional manner and ensures precipitation of iron compounds necessary
for co-precipitation of arsenic and other trace species.
In a preferred embodiment, the water is returned once or several times after precipitation
and separation of the iron compounds for renewed contact with the iron-containing mate-
rial. With this treatment, the content of arsenic and other trace species may be reduced
Thus, the method according to the invention permits to lower the content of substances
harmful to health and environment, such as As and residual pesticides, in drinking water
to a harmless low level below limits currently in force and in a profitable manner.
According to a particular embodiment, water is contacted with an iron-containing material
under low-oxygen conditions, e. g.. in a suitable closed system, such as a closed box.
Thus, the formation of Fe(lll)-containing compounds and premature precipitation of iron
compounds is reduced.
The scope of the applicability of the invention will appear from the detailed description be-
low, it is apparent, however, that the detailed description and the specific examples illus-
trating preferred embodiments of the invention are only given by way of example, and
various alterations and modifications falling within the scope of the invention will become
apparent to those skilled in the art upon reading the detailed description.
Best Modes for Carrying out the Invention
During conventional treatment of groundwater to be used as drinking water one treatment
process is the removal of the iron and manganese content from groundwater. This is ac-
complished by simple oxidation and filtration at waterworks, Traditionally, this treatment is
carried out, because groundwater often contains iron in such high concentrations that it
has to be removed prior to distribution. The content of iron compounds in the groundwa-
ter, said compounds mainly being Fe(ll) compounds, is not harmful to health, but may
cause problems with bacterial growth (iron-oxidizing bacteria), precipitation in the water
distribution system, discoloration of clothes and basins, bad taste and clouding. Iron is
removed by means of aeration and subsequent precipitation and filtration.
As mentioned above, several contaminant trace species co-precipitate with iron com-
pounds, so that it is normally not a problem to comply with established limits of such sub-
However, not all waterworks have groundwater with such high iron concentrations. In such
waterworks, the new more restrictive limits, in the case of As lowered by one order of
magnitude from 50 µm/l to 5 µm/I, cause serious problems, since co-precipitation with
modest amounts of iron compounds is not sufficiently effective.
It has now been found, that the concentrations of As and other harmful substances in
drinking water may be lowered in a surprisingly simple manner to well below the obligatory
limits according to the present method by ensuring a sufficiently high iron concentration in
the water prior to conventional oxidation and precipitation of oxidized iron compounds,
typically Fe(lll) compounds.
Preferably, the iron concentration in water is increased by contacting the water intimately
with an iron material having a suitably large contact surface. An inexpensive material is
iron swarfs, available as a waste product of machining, said swarfs having being calci-
nated prior to their use to remove residual cutting oil. Another material is iron ore.
in practice, the contact between water and the iron material may be achieved by spraying
a suitable bed of iron material, for example a layer of iron swarfs having a thickness of
10-30 cm and arranged in a perforated tray made of plastic or stainless steel. The thick-
ness of the bed of iron swarfs is adjusted so that the desired amount of iron to be added
to the water is achieved. The tray is provided with a plurality of holes, e. g. having a di-
ameter of 3-4 mm, at the bottom of the tray. The water is supplied to the bed of iron
swarfs in a manner ensuring a good and uniform distribution This may be accomplished
in a manner well-known to a person skilled in the art, for example by means of a suitable
number of nozzles or from an overhead distributor tray adapted as a drip tray with a plu-
rality of holes so that the bed of iron swarfs is constantly sprayed with water. The water
thereby takes up rust/iron, and the content of iron in the water increases.
The water thus enriched with iron is subsequently treated in a traditional manner by oxida-
tion, precipitation and separation, usually by means of sedimentation and/or filtration, thus
obtaining pure drinking water, said water not only being freed from iron and manganese
again, but also freed from various contaminant trace species, such as for example As and
pesticides co-precipitated with Fe(lll) compounds.
As mentioned above, iron oxidation may be accomplished in a manner known per se in a
conventional aeration device, such as a splasher, drip-type sheet, cascade aerator or by
blowing in air or oxygen, resulting in precipitation and separation of Fe(lll) compounds. In
an advantageous embodiment, oxidation is accomplished in an aeration device of the type
described in EP Patent No. 1 070 022. Usually, this device achieves an oxidation of water
10 times more effective compared to common known cascade aerators. Using suitable
dimensioning a saturation of about 95% may thus be obtained.
EP 1 070 022 provides an aeration device for the treatment of water by means of a perfo-
rated plate being a plate formed with holes where water flows through at the beginning of
the treatment and is changed into drops. Below the perforated plate, there is an assembly
of ensuring a division of the drops The assembly comprise several layers of tubular ele-
ments, the walls of each of said pipes being constructed of a wire net. The tubular ele-
ments in each layer are arranged horizontally and mutually in parallel, while the tubular
elements in adjacent layers are arranged perpendicular to each other.
The method of operation of the aeration device includes groundwater being pumped to the
top of the unit and running down over the tubular elements so that the water drops im-
pinge on obstacles 60-80 times and are divided into microdrops prior to the water being
collected in a collection container or basin, wherefrom the purified water may be with-
drawn. Oxidized iron compounds are precipitated in the collection container, wherefrom
they may be removed as necessary by light flushing. Subsequently, the water may be fil-
tered, if required, typically in an sand filter, to ensure further precipitation of iron and trace
species. In many cases however, separation in the collection container is sufficiently ef-
fective so that sand filtration may be dispensed with.
In combination with the above-mentioned aeration device the bed of iron material men-
tioned above, for example a bed of iron swarfs in a perforated tray made of plastic or
stainless steel mentioned above, may be arranged directly above the aeration unit. Ac-
cordingly, groundwater may be pumped directly to the distributor tray above the bed of
iron swarfs, where it passes first through the bed of iron filings without further pumps,
where it is enriched with oxidizable iron compounds, whereupon it passes through the
aeration device ensuring precipitation of the iron compounds and co-precipitation of con-
taminant trace species
As mentioned above, precipitation in the collection container or basin is often satisfactory
in the known aeration device, if necessary however, residual iron compounds with bound
trace species may be precipitated during subsequent filtration, e. g. in a sand filter.
In practice, the bed of iron-containing material is dimensioned such that it is ensured that
water takes up the amount of iron compounds necessary for binding present As, pesti-
cides and other harmful trace species for binding them effectively to the iron which is pre-
cipitated during the aeration process.
To begin with, the invention was tested with respect to fulfilling the new more restrictive
limit for arsenic in drinking water. However, initial experiments have also confirmed co-
precipitation of pesticides and MTBE (methyl t-butyl ether) together with the oxidized iron
One potential application of the method according to the invention relates to the removal
of residual arsenic from chemically treated waste materials, such as chemically treated
timber waste. Timber waste is immersed in a water basin, where residua! arsenic eventu-
ally permeates into the water The water from the basin is continuously pumped through a
bed of iron-containing compounds and further through an aeration device and from there
recycled back to the water basin. Precipitated iron compounds bind the arsenic dissolved
in the water and settle at the bottom of the basin. The process continues, until the arsenic
has been washed out of the wood to a satisfactory extent.
The method and device according to the invention are uncomplicated and inexpensive.
The enrichment of water with iron requires no critical precise dosing of iron compounds,
since a suitable system for distributing the water across the iron swarfs in a plastic tray
having suitably dimensioned holes has been found to work in an effective manner over a
long period of time, such as 6 months, until the iron swarfs ought to be exchanged. Ac-
cordingly, the device may be monitored by persons without any special training and is just
as usable in industrial countries as it is in developing countries.
Brief Description of the Drawing
The invention is explained in detail below with reference to the drawing, in which
Fig. 1 is a schematic view of a device according to the invention having a bed of iron
swarfs arranged above an aeration device, and
Fig.. 2 shows the bed of iron swarfs in a plastic tray.
As shown in Fig. 1, groundwater is pumped with a pump 1 over the top of the device to a
drip tray 2, wherefrom it is uniformly distributed across a bed of iron swarfs 3 approx.
10 cm thick, said bed being arranged in a perforated plastic tray 4. During its passage
through the bed 3 water takes up iron, predominantly in the form of Fe(ll) compounds.
From the plastic tray 4 water drips down to an aeration device of the type described in
EP 1 070 022, where it is aerated effectively in an aeration chamber 5 filled with special
tubular elements as described above, said tubular elements ensuring an air saturation of
up to 95%, The aerated water is directed to a collection container 6, where precipitated
iron compounds settle with co-precipitation of arsenic and other trace species. In a simple
embodiment, pure drinking water may be taken out directly from the collection container 6,
since sedimentation of the iron precipitate ensures sufficient separation. To improve
sedimentation, the water from the collection container 6 may be fed to a sand filter 8 by
means of a pump 7, wherefrom the pure drinking water 9 may be taken out.
In another embodiment, the aeration chambers may be formed as an empty gravity
chamber, where water drops from the perforated plastic tray 4 are aerated during the free
fall down in the collection container 6.
if the treated drinking water has an As content of above the limit 5 µm/l, the water in the
collection container 6 may be recycled to the drip tray 2 at the top of the device through a
pipe 10 using a pump for renewed treatment with iron addition and subsequent aeration
Above an aeration device of the type described in EP 1 070 022 (Microdrop-MP1 L, avail-
able from MicroDrop Aqua, Taastrup, Denmark), there is arranged a bed of iron filings
having a thickness of 10 cm in an approx. 700 x 550 mm perforated plastic tray, said bed
having an overhead drip tray for distributing the water. Groundwater having a low iron
content and 30 ppm As was introduced above the drip tray in an amount of 0,5 m3/h.
When passing through the bed of iron filings, the water took up approx. 1 mg iron per litre.
After aeration to a saturation of up to 95% with precipitation of iron in the collection con-
tainer, the water withdrawn therefrom had an As content of 10 ppm, i e. one third of the
original As content.
After a single passage, the water may be recycled for a new iron treatment, aeration and
precipitation, thus reducing the As content to approx. 3-4 ppm, a value below the new
more restrictive limit for drinking water.
The present example illustrates a device according to the invention provided for a flow of
0,05-1,0 m3/h and set up at a waterworks. Iron swarfs are arranged in a bed with a thick-
ness of 10 cm in a perforated 800 x 605 mm plastic tray. Before start-up of the device, the
iron swarfs were sprinkled with water for 4 days to ensure rust formation on the surface of
the iron swarfs. On the first day after start-up of the device, the supplied groundwater, the
water after passage through the iron filings, the water in the collection container (tank) af-
ter the aerator and the water in the outflow of a sand filter, respectively, were analysed.
The results are shown in table 1.
As is apparent, the limit for As of 5 µg/l has been complied with.
The iron swarfs used are an inexpensive material usable for 6 months, based on experi-
ence. When treating groundwater with iron swarfs prior to aeration, severe coating of the
iron swarfs are avoided, said coatings being capable of blocking the release of iron com-
pounds into the water. To avoid the formation of coatings, the water ought not to remain in
contact with the bed of iron swarfs over a longer period. In practice, the water is treated
immediately after iron enrichment by passing through a bed of iron swarfs in an aeration
device with strong aeration, whereupon iron and arsenic are precipitated, partly in the
subsequent collection tank and partly in the sand filter.
The invention having been described herein, it is apparent that it may be modified in many
ways. Such variations are not to be considered as deviating from the scope of the inven-
tion, and all such modifications apparent to those skilled in the art are to be understood as
being comprised by the scope of the appended claims.
Application no. PCT/DK2006/000250
Our ret 82125 Zeu/NG
28 June 2007
Proposed amended claims
1. A method for purifying water from contaminant trace species, especially arsenic,
by treating said water with iron and co-precipitating trace species during oxidation, and
precipitation of iron compounds with subsequent Separation, characterized in that
a) first, the water is contacted without aeration with an iron-containing material for enrich-
ing the water with iron compounds,
b) then, the iron-enriched-water is oxidized for co-precipitation of the contaminant trace
species together with oxidized iron compounds, and
c) finally, the precipitated compounds are separated from the water.
2. The method according to claim 1, characterized in that the water in step a) is en-
riched with Fe(ll) compounds.
3. The method according to claim 1, characterized in that the iron-containing mate-
rial is iron ore or metallic iron, including iron particles, iron filings or swarfs, or any other
natural iron-containing material having a large surface.
4. The method according to claim 1, 2 or 3, characterized in that the water is con-
tacted with an iron-containing material in a closed system.
5. The method according to any of the preceding claims, characterized in that the
contact between iron and water is achieved by natural spraying of an iron-containing ma-
terial arranged In a bed mounted above an aerator,
6. The method according to claim 1, characterized in that after co-precipitation of
the trace species during oxidation and precipitation of iron compounds with subsequent
separation, the water is recycled once or several times for renewed treatment comprising
adding an additional amount of iron compounds with subsequent oxidation, precipitation of
iron compounds and separation.
7. The method according to any of the preceding claims, characterized in that the
co-precipitated trace species comprise arsenic and/or pesticides.
Application no. PCT/DK2006/000250
Our ref: 82125 2eu/NG
38 June 2007
8. A device for purifying water from contaminant trace species by co-precipitating
the trace species comprising an aerator (5) for oxidation and precipitation of iron com-
pounds with subsequent separation, characterized in that a non aerated assembly (2, 3,
4) for supplying iron compounds to the water is Incorporated prior to the aerator (5).
9. The device according to claim 8, characterized in that the assembly for supplying
iron compounds comprises a distributor means (2) for distributing water across a bed (3)
of iron particles, iron filings or swarfs, iron ore or any other natural iron-containing material
having a large surface, as well as one or more openings below the bed for the outflow or
10. The device according to claim 8 or 9, characterized in that the assembly (2, 3, 4)
for supplying iron compounds to the water is arranged above a perforated plate to form
drops, said perforated plate being positioned above a drop division assembly composed
of a plurality of tubular elements in the form of pipes having pipe walls made of wire net,
said tubular elements being placed in horizontal layers of several parallel tubular elements
stacked in such a way that the longitudinal axis of the tubular elements in one layer are
angularly displaced in relation to the tubular elements in the one or more adjacent layers,
preferably with an angle of 90°.
11. The device according to claim 8 to 10, characterized in that it further comprises a
recirculation pipe (10) for recycling the treated water to the assembly (2, 3, 4) for supply-
ing of iron compounds to the water.
A method and a device for purifying water from contaminant trace species, especially arsenic,
by co-precipitating trace species during oxidation and precipitation of iron compounds
with subsequent separation. The co-precipitation is improved by contacting the
water with an iron-containing material prior to oxidation to increase the iron content of the
water. Arsenic and other trace species harmful to health may be removed from water effectively
and in a simple manner, thus being able to comply with the more restrictive limits
of arsenic in drinking water.
|Indian Patent Application Number||4228/KOLNP/2007|
|PG Journal Number||28/2013|
|Date of Filing||02-Nov-2007|
|Name of Patentee||MICRODROP ACQUA APS|
|Applicant Address||HELGESHOJ ALLE 12, HOJE TAASTRUP DK-2630, TAASTRUP|
|PCT International Classification Number||C02F 1/52, C02F 1/58|
|PCT International Application Number||PCT/DK2006/000250|
|PCT International Filing date||2006-05-11|