Title of Invention	METHOD FOR REMOVING SULPHATE AND HEAVY METALS FROM WASTE WATER
Abstract	The invention relates to a method for removing sulphate and heavy metals from waste water. Said method consists of the following steps: a) in a first treatment step (I) hydrogen sulphide is guided through the waste water, heavy metals that are present in the waste water are precipitated as sulphide, and are removed from the waste water, b) in a second treatment step (II), calcium sulphate is precipitated from the waste water by adding a precipitation auxiliary agent, c) the calcium sulphate is removed in the second treatment step (II) and one part thereof is guided to a third treatment step (III) in which sulphate is converted into hydrogen sulphide with the aid of sulphate-reducing bacteria, d) hydrogen sulphide formed in the third treatment step (III) is guided back to the first treatment step (I).

Title of Invention

METHOD FOR REMOVING SULPHATE AND HEAVY METALS FROM WASTE WATER

Abstract

The invention relates to a method for removing sulphate and heavy metals from waste water. Said method consists of the following steps: a) in a first treatment step (I) hydrogen sulphide is guided through the waste water, heavy metals that are present in the waste water are precipitated as sulphide, and are removed from the waste water, b) in a second treatment step (II), calcium sulphate is precipitated from the waste water by adding a precipitation auxiliary agent, c) the calcium sulphate is removed in the second treatment step (II) and one part thereof is guided to a third treatment step (III) in which sulphate is converted into hydrogen sulphide with the aid of sulphate-reducing bacteria, d) hydrogen sulphide formed in the third treatment step (III) is guided back to the first treatment step (I).

Full Text	Description Method for removing sulfate and heavy metals from waste water The invention relates to a method for processing waste waters containing sulfate and heavy metals. Such waste waters are produced in large amounts, in particular, in mining during transport, refining and extraction of metal ores. Conventionally, sulfate is precipitated out of such waste waters as calcium sulfate by pH reduction and addition of a precipitant such as milk of lime, and removed from the waste water using sedimentation tanks or filter stages. Owing to the heavy metal content of the waste waters, the sulfate sludges must be treated as special waste and stored in special landfills at high expense. US 5,587,079 discloses a method in which the heavy metals are precipitated out by introducing hydrogen sulfide and are separated off. Some of the sulfate- containing water is fed to a bioreactor in which sulfate is converted to H2S using sulfate-reducing bacteria, which H2S is used for the precipitation of heavy metals. Excess sulfate is converted to H2S in the bioreactor, wherein this is reacted to form metal sulfides. A disadvantage of this method is, especially, that the total amount of waste water must be passed through the bioreactor in order to separate off all of the sulfate contained therein. This requires not only a very large bioreactor having corresponding operating and service expenditure, but in addition further method steps and corresponding apparatuses for reacting the hydrogen sulfide generated to form metal sulfides. A further disadvantage is that in the case of large amounts of sulfate, a correspondingly large amount cf metal sulfides is formed which are in addition to the metal sulfides which are precipitated out of the waste water containing heavy metals. Therefore, in total a very large amount of metal sulfides is produced which, in the lack of possibilities for reutilization lead to considerable problems of disposal and/or landfill. For instance, there is the risk, for example, that on contact with acidic water, hydrogen sulfide is expelled from the sulfides. In the light of this the object of the invention is to propose an alternative processing method for waste water containing sulfate and heavy metals, by which method, in particular said disadvantages can be avoided. This object is achieved according to claim 1 by a method in which, in a first treatment stage, hydrogen sulfide is passed through the waste water. In this process heavy metals present in the waste water, such as copper, iron or manganese, are precipitated cut as sulfides and removed from the waste water before, in a second treatment stage, calcium sulfate is precipitated out of the waste water by addition of a precipitant. This procedure has the advantage that the separation of the sulfate from the waste water can proceed essentially only in a single step, if appropriate with downstream connection of filtering for separating off residual water. In contrast, separating off sulfate in the known method requires at least two steps, namely passing virtually all of the amount of waste water through the bioreactor and subsequent reaction to form metal sulfides, which obviously requires the use of corresponding salts, that is an additional expenditure on chemicals. In contrast to metal sulfides, precipitated calcium sulfate (gypsum) can be utilized in the construction industry as additive for production of bricks or as binder. It is further advantageous that in the proposed method only a relatively small bioreactor is required since it serves exclusively for generating the amount of hydrogen sulfide required for precipitating out the heavy metals present in the waste water. The respective amount of hydrogen sulfide required may be controlled in a simple manner by the amount of calcium sulfate fed to the third treatment stage, namely in such a manner that stoichiometric fractions of sulfides and heavy metal ions are present. In order, for example, in the case of fluctuating heavy metal content, to reduce the expenditure on analysis, an excess of hydrogen sulfide, in particular 20 mol%, can be employed, compared with the stoichiometric amount. In the case of lower heavy metal contents, unused hydrogen sulfide can, for example, be temporarily stored, in order to be reused when required. The precipitant used is preferably calcium aluminate. The use of sodium aluminate is also conceivable. The invention will now be described in more detail with reference to the accompanying drawing which shows a flow diagram of a method according to the invention. For the waste water treatment method in question, essentially in total three treatment stages are required which are characterized by I-III in the drawing. A waste water to be purified is first fed to the treatment stage I. This comprises a reactor 1 for treating the waste water with hydrogen sulfide. The reactor 1 is charged with waste water via a line 2. Via a line 3, hydrogen sulfide is fed to the reactor 1 at a position lying in its bottom region. In order to distribute the hydrogen sulfide as finely as possible in the waste water, a circulation appliance is present. This comprises a circulation line 5 which branches off in the lid region of the reactor and opens out into the reactor 1 at a lower position, in which circulation line a pump 6 is arranged. This circulates the waste water at high velocity, wherein strong turbulence occurs within the reactor 1, which turbulence promotes mixing of the reactants. Heavy metal sulfides formed by introducing hydrogen sulfide are conducted upward by the flow of the waste water and pass via an outlet 7 arranged in the region adjacent to the lid into a filter unit 8 which is arranged downstream of the reactor 1. Here, the heavy metal sulfides are filtered out of the waste water. In the bottom region of the filter unit 8, primary sludge containing heavy metal sulfide is taken off via a line 9 and subjected to a filtration, for example using a plate filter press 10. The filtrate and/or waste water purified of heavy metal sulfides is withdrawn from the filter unit 8 via a line 12 and fed to the treatment stage II. The treatment stage II comprises a settling container 13 having a funnel- or wedge-shaped bottom 14. At a position close to the top 15 of the settling container 13, the line 12 coming from the filter unit 8 opens out into the settling container 13. From a storage container 16, calcium aluminate as precipitant is introduced into the settling container 13. To accelerate the precipitation process, a stirrer appliance 17 is present in the settling container 13, which stirrer appliance is driven by a motor 18. The precipitated calcium sulfate, when the stirrer appliance 17 is still, collects at the bottom 14 of the settling container 13 and is taken off as secondary sludge via a line 19 whereas waste water essentially freed from sulfate is withdrawn via a line 20 which is arranged close to the top 15. A part of the secondary sludge is fed to the treatment stage III via a line 22 which branches off from the line 19. The treatment stage III is formed essentially by a bioreactor 23 in which sulfate is converted to hydrogen sulfide in a manner known per se using sulfate-reducing bacteria. In order that this conversion can take place, anoxic conditions are maintained in the bioreactor 23. Reaction of the sulfate to form hydrogen sulfide reguires an electron donor or a carbon source. This is fed to the bioreactor 23 in the form of organically polluted waste water 24 via a storage container 25 and a line 26. Hydrogen sulfide and carbon dioxide form as reaction products of the microbiological metabolic processes. The reactor 1 of treatment stage I is charged with this gas mixture via the line 3. By means of the reactions in the bioreactor 23, solids especially of organic nature are formed which, via a line 27 which opens out in a region close to the bottom of the bioreactor 23, are fed to a filter unit, for instance likewise a filter plate 10. The filtrate can if appropriate be recirculated to the bioreactor 23. Patent claims 1. A method of removing sulfate and heavy metals from waste water having the following steps: a) in a first treatment stage (I), hydrogen sulfide is passed through the waste water, wherein heavy metals present in the waste water are precipitated out as sulfides and removed from the waste water, b) in a second treatment stage (II), calcium sulfate is precipitated out of the waste water by addition of a precipitant, c) the calcium sulfate is removed from the second treatment stage (II) and a part thereof is fed to a third treatment stage (III) in which sulfate is converted to hydrogen sulfide with the aid of sulfate- reducing bacteria, d) hydrogen sulfide which is formed in the third treatment stage 'III) is fed to the first treatment stage (I). 2. The methc:i as claimed in claim 1, in which the precipitant used is calcium aluminate. 3. The method as claimed in claim 1 or 2, in which calcium sulfate is fed to the third treatment stage (III) until at least an amount of hydrogen sulfide required for the stoichiometric reaction of the heavy metals contained in the waste water is formed. 4. The method as claimed in claim 3, in which a hydrogen sulfide excess of 20 mol% is employed. The invention relates to a method for removing sulphate and heavy metals from waste water. Said method consists of the following steps: a) in a first treatment step (I) hydrogen sulphide is guided through the waste water, heavy metals that are present in the waste water are precipitated as sulphide, and are removed from the waste water, b) in a second treatment step (II), calcium sulphate is precipitated from the waste water by adding a precipitation auxiliary agent, c) the calcium sulphate is removed in the second treatment step (II) and one part thereof is guided to a third treatment step (III) in which sulphate is converted into hydrogen sulphide with the aid of sulphate-reducing bacteria, d) hydrogen sulphide formed in the third treatment step (III) is guided back to the first treatment step (I).

Full Text

Description
Method for removing sulfate and heavy metals from waste water
The invention relates to a method for processing waste waters
containing sulfate and heavy metals. Such waste waters are
produced in large amounts, in particular, in mining during
transport, refining and extraction of metal ores.
Conventionally, sulfate is precipitated out of such waste
waters as calcium sulfate by pH reduction and addition of a
precipitant such as milk of lime, and removed from the waste
water using sedimentation tanks or filter stages. Owing to the
heavy metal content of the waste waters, the sulfate sludges
must be treated as special waste and stored in special
landfills at high expense. US 5,587,079 discloses a method in
which the heavy metals are precipitated out by introducing
hydrogen sulfide and are separated off. Some of the sulfate-
containing water is fed to a bioreactor in which sulfate is
converted to H2S using sulfate-reducing bacteria, which H2S is
used for the precipitation of heavy metals. Excess sulfate is
converted to H2S in the bioreactor, wherein this is reacted to
form metal sulfides. A disadvantage of this method is,
especially, that the total amount of waste water must be passed
through the bioreactor in order to separate off all of the
sulfate contained therein. This requires not only a very large
bioreactor having corresponding operating and service
expenditure, but in addition further method steps and
corresponding apparatuses for reacting the hydrogen sulfide
generated to form metal sulfides. A further disadvantage is
that in the case of large amounts of sulfate, a correspondingly
large amount cf metal sulfides is formed which are in addition
to the metal sulfides which are precipitated out of the waste
water containing heavy metals. Therefore, in total a very large
amount of metal sulfides is produced which, in the lack of
possibilities for reutilization lead to considerable problems

of disposal and/or landfill. For instance, there is the risk,
for example, that on

contact with acidic water, hydrogen sulfide is expelled from
the sulfides.
In the light of this the object of the invention is to propose
an alternative processing method for waste water containing
sulfate and heavy metals, by which method, in particular said
disadvantages can be avoided.
This object is achieved according to claim 1 by a method in
which, in a first treatment stage, hydrogen sulfide is passed
through the waste water. In this process heavy metals present
in the waste water, such as copper, iron or manganese, are
precipitated cut as sulfides and removed from the waste water
before, in a second treatment stage, calcium sulfate is
precipitated out of the waste water by addition of a
precipitant. This procedure has the advantage that the
separation of the sulfate from the waste water can proceed
essentially only in a single step, if appropriate with
downstream connection of filtering for separating off residual
water. In contrast, separating off sulfate in the known method
requires at least two steps, namely passing virtually all of
the amount of waste water through the bioreactor and subsequent
reaction to form metal sulfides, which obviously requires the
use of corresponding salts, that is an additional expenditure
on chemicals. In contrast to metal sulfides, precipitated
calcium sulfate (gypsum) can be utilized in the construction
industry as additive for production of bricks or as binder. It
is further advantageous that in the proposed method only a
relatively small bioreactor is required since it serves
exclusively for generating the amount of hydrogen sulfide
required for precipitating out the heavy metals present in the
waste water.
The respective amount of hydrogen sulfide required may be
controlled in a simple manner by the amount of calcium sulfate

fed to the third treatment stage, namely in such a manner that
stoichiometric fractions of sulfides and heavy metal ions are
present. In order, for example, in the case of fluctuating
heavy

metal content, to reduce the expenditure on analysis, an
excess of hydrogen sulfide, in particular 20 mol%, can be
employed, compared with the stoichiometric amount. In the case
of lower heavy metal contents, unused hydrogen sulfide can, for
example, be temporarily stored, in order to be reused when
required.
The precipitant used is preferably calcium aluminate. The use
of sodium aluminate is also conceivable.
The invention will now be described in more detail with
reference to the accompanying drawing which shows a flow
diagram of a method according to the invention.
For the waste water treatment method in question, essentially
in total three treatment stages are required which are
characterized by I-III in the drawing. A waste water to be
purified is first fed to the treatment stage I. This comprises
a reactor 1 for treating the waste water with hydrogen sulfide.
The reactor 1 is charged with waste water via a line 2. Via a
line 3, hydrogen sulfide is fed to the reactor 1 at a position
lying in its bottom region. In order to distribute the hydrogen
sulfide as finely as possible in the waste water, a circulation
appliance is present. This comprises a circulation line 5 which
branches off in the lid region of the reactor and opens out
into the reactor 1 at a lower position, in which circulation
line a pump 6 is arranged. This circulates the waste water at
high velocity, wherein strong turbulence occurs within the
reactor 1, which turbulence promotes mixing of the reactants.
Heavy metal sulfides formed by introducing hydrogen sulfide are
conducted upward by the flow of the waste water and pass via an
outlet 7 arranged in the region adjacent to the lid into a
filter unit 8 which is arranged downstream of the reactor 1.
Here, the heavy metal sulfides are filtered out of the waste
water. In the bottom region of the filter unit 8, primary
sludge containing heavy metal sulfide is taken off via a line 9

and subjected to a filtration, for example using a plate filter
press 10. The filtrate and/or waste water purified of heavy
metal sulfides is withdrawn from the filter unit 8 via a line
12 and fed to the treatment stage II.
The treatment stage II comprises a settling container 13 having
a funnel- or wedge-shaped bottom 14. At a position close to the
top 15 of the settling container 13, the line 12 coming from
the filter unit 8 opens out into the settling container 13.
From a storage container 16, calcium aluminate as precipitant
is introduced into the settling container 13. To accelerate the
precipitation process, a stirrer appliance 17 is present in the
settling container 13, which stirrer appliance is driven by a
motor 18. The precipitated calcium sulfate, when the stirrer
appliance 17 is still, collects at the bottom 14 of the
settling container 13 and is taken off as secondary sludge via
a line 19 whereas waste water essentially freed from sulfate is
withdrawn via a line 20 which is arranged close to the top 15.
A part of the secondary sludge is fed to the treatment stage
III via a line 22 which branches off from the line 19.
The treatment stage III is formed essentially by a bioreactor
23 in which sulfate is converted to hydrogen sulfide in a
manner known per se using sulfate-reducing bacteria. In order
that this conversion can take place, anoxic conditions are
maintained in the bioreactor 23. Reaction of the sulfate to
form hydrogen sulfide reguires an electron donor or a carbon
source. This is fed to the bioreactor 23 in the form of
organically polluted waste water 24 via a storage container 25
and a line 26. Hydrogen sulfide and carbon dioxide form as
reaction products of the microbiological metabolic processes.
The reactor 1 of treatment stage I is charged with this gas
mixture via the line 3. By means of the reactions in the
bioreactor 23, solids especially of organic nature are formed
which, via a line 27 which opens out in a region close to the
bottom of the bioreactor 23,

are fed to a filter unit, for instance likewise a filter plate
10. The filtrate can if appropriate be recirculated to the
bioreactor 23.

Patent claims
1. A method of removing sulfate and heavy metals from waste
water having the following steps:
a) in a first treatment stage (I), hydrogen sulfide is
passed through the waste water, wherein heavy metals
present in the waste water are precipitated out as
sulfides and removed from the waste water,
b) in a second treatment stage (II), calcium sulfate is
precipitated out of the waste water by addition of a
precipitant,
c) the calcium sulfate is removed from the second
treatment stage (II) and a part thereof is fed to a
third treatment stage (III) in which sulfate is
converted to hydrogen sulfide with the aid of sulfate-
reducing bacteria,
d) hydrogen sulfide which is formed in the third treatment
stage 'III) is fed to the first treatment stage (I).

2. The methc:i as claimed in claim 1, in which the precipitant
used is calcium aluminate.
3. The method as claimed in claim 1 or 2, in which calcium
sulfate is fed to the third treatment stage (III) until at
least an amount of hydrogen sulfide required for the
stoichiometric reaction of the heavy metals contained in the
waste water is formed.
4. The method as claimed in claim 3, in which a hydrogen
sulfide excess of 20 mol% is employed.

The invention relates to a method for removing sulphate and heavy metals from
waste water. Said method consists of the following steps: a) in a first treatment
step (I) hydrogen sulphide is guided through the waste water, heavy metals that
are present in the waste water are precipitated as sulphide, and are removed
from the waste water, b) in a second treatment step (II), calcium sulphate is
precipitated from the waste water by adding a precipitation auxiliary agent, c)
the calcium sulphate is removed in the second treatment step (II) and one part
thereof is guided to a third treatment step (III) in which sulphate is converted
into hydrogen sulphide with the aid of sulphate-reducing bacteria, d) hydrogen
sulphide formed in the third treatment step (III) is guided back to the first
treatment step (I).

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Patent Number

269690

Indian Patent Application Number

619/KOLNP/2009

PG Journal Number

45/2015

Publication Date

06-Nov-2015

Grant Date

30-Oct-2015

Date of Filing

17-Feb-2009

Name of Patentee

SIEMENS AKTIENGESELLSCHAFT

Applicant Address

WITTELSBACHERPLATZ 2, 80333 MUNCHEN

Inventors:

#	Inventor's Name	Inventor's Address
1	MICHAEL RIEBENSAHM	HUEICOLLA 14042, SANTIAGO, CHILE

PCT International Classification Number

C02F 1/52,C02F 3/34

PCT International Application Number

PCT/EP2007/058294

PCT International Filing date

2007-08-10

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10 2006 038 207.2	2006-08-16	Germany