U.S. patent application number 13/883586 was filed with the patent office on 2013-09-05 for reactor for recovering phosphate salts from a liquid.
This patent application is currently assigned to Fraunhofer-Gesellschaft zur Forderung der angewandten Forschung e.V.. The applicant listed for this patent is Jennifer Bilbao, Dieter Bryniok, Alejandra Campos, Siegfried Egner. Invention is credited to Jennifer Bilbao, Dieter Bryniok, Alejandra Campos, Siegfried Egner.
Application Number | 20130228457 13/883586 |
Document ID | / |
Family ID | 44907865 |
Filed Date | 2013-09-05 |
United States Patent
Application |
20130228457 |
Kind Code |
A1 |
Bilbao; Jennifer ; et
al. |
September 5, 2013 |
Reactor for recovering phosphate salts from a liquid
Abstract
The invention relates to a reactor (10) for completely
separating phosphate from a liquid and for recovering phosphate
salts, comprising a housing (12) and two electrodes having
differing polarities, wherein a sacrificial anode (16) made of a
magnesium-containing material and an inert cathode (18) are
arranged concentrically inside the housing (12).
Inventors: |
Bilbao; Jennifer;
(Stuttgart, DE) ; Bryniok; Dieter; (Dusslingen,
DE) ; Campos; Alejandra; (Stuttgart, DE) ;
Egner; Siegfried; (Adelsheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bilbao; Jennifer
Bryniok; Dieter
Campos; Alejandra
Egner; Siegfried |
Stuttgart
Dusslingen
Stuttgart
Adelsheim |
|
DE
DE
DE
DE |
|
|
Assignee: |
Fraunhofer-Gesellschaft zur
Forderung der angewandten Forschung e.V.
Munchen
DE
|
Family ID: |
44907865 |
Appl. No.: |
13/883586 |
Filed: |
October 31, 2011 |
PCT Filed: |
October 31, 2011 |
PCT NO: |
PCT/EP2011/069119 |
371 Date: |
May 6, 2013 |
Current U.S.
Class: |
204/240 ;
204/272 |
Current CPC
Class: |
C02F 1/463 20130101;
C02F 2001/46152 20130101; C02F 2101/105 20130101; C02F 2201/003
20130101; C02F 11/04 20130101; C25B 9/00 20130101; C02F 2001/46133
20130101; C02F 1/001 20130101; C02F 2201/4617 20130101 |
Class at
Publication: |
204/240 ;
204/272 |
International
Class: |
C25B 9/00 20060101
C25B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 2010 |
DE |
10 2010 050 692.3 |
Claims
1.-11. (canceled)
12. A reactor for complete crystallization and recovery of MAP
(magnesium ammonium phosphate) and PMP (potassium magnesium
phosphate) from a liquid and recovery of phosphate salts, the
reactor comprising: a housing; a first electrode and a second
electrode, wherein the first and second electrodes have different
polarity; wherein the first electrode is a sacrificial anode of a
magnesium-containing material; wherein the second electrode is an
inert cathode; wherein the sacrificial anode and the inert cathode
are arranged concentrically relative to each other; a return line
connected to the housing, wherein seed crystals are supplied to the
reactor via the return line.
13. The reactor according to claim 11, wherein the housing is
comprised of an electrically conducting material and serves as the
inert cathode.
14. The reactor according to claim 11, wherein the sacrificial
anode is comprised of magnesium.
15. The reactor according to claim 11, further comprising an inlet,
an outlet, and a removal device.
16. The reactor according to claim 15, wherein the return line
branches off the outlet or branches of the removal device.
17. The reactor according to claim 11, that the reactor is flowed
through in vertical direction from the bottom to the top.
18. The reactor according to claim 11, wherein the reactor is
flowed through in vertical direction from the top to the
bottom.
19. The reactor according to claim 11, further comprising a filter
that separates crystals of MAP, PMP, and phosphate salts from the
liquid.
20. The reactor according to claim 11, wherein the housing of the
reactor is closed.
21. The reactor according to claim 11, wherein the housing of the
reactor is open.
22. The reactor according to claim 11, comprising a slanted
bottom.
23. The reactor according to claim 11, comprising a direct current
source, wherein a positive pole is connected to the sacrificial
anode and a negative pole is connected to the inert cathode.
Description
[0001] Reactor for recovering phosphate salts from a liquid
[0002] The invention concerns a reactor for complete separation of
phosphate from a liquid and recovery of phosphate salts, comprising
a housing and two electrodes of different polarity.
[0003] Phosphate salts such as magnesium ammonium phosphate (in the
following abbreviated as MAP) or potassium magnesium phosphate (in
the following abbreviated as PMP) are high-value plant adjuvants
for which there is high demand. The elements nitrogen, potassium,
magnesium, and phosphate of which these plant adjuvants are
comprised are typically contained in all solid or liquid organic
waste materials. While potassium, magnesium and other ions are
present in the form of water-soluble cations, nitrogen and
phosphate are predominantly bound to or in organic material or cell
mass. Accordingly, a major proportion of nitrogen and phosphate are
not available for the production of plant adjuvants. For this
reason it is necessary to convert nitrogen and phosphate into their
inorganic form that is suitable for precipitation.
[0004] The spontaneous precipitation of MAP or PMP is limited by
the usually very low magnesium concentration in wastewater. Known
is the addition of magnesium hydroxide, magnesium oxide or soluble
magnesium salts for MAP precipitation. The disadvantage in this
context is the bad solubility of the oxides as well as of the
salt-like hydroxides. Upon addition of magnesium hydroxide or
magnesium oxide to the wastewater, these compounds dissolve only
very slowly and with a minimal proportion. This has the result that
it is necessary to continuously perform stirring or mixing which,
however, causes extra expenditure in regard to technology and
energy and thus also with respect to costs. Moreover, both
compounds, because of their bad solubility, must be added in
over-stoichiometric amounts because otherwise an incomplete
precipitation of the desired plant adjuvants occurs and significant
quantities of phosphate remain in the wastewater. When magnesium
salts are beforehand transferred into a solution, the efficiency of
the method decreases because of the dilution with water.
[0005] The optimal pH value for precipitation of MAP is at 9.
Wastewater has usually pH values between 5 and 7. Therefore, for
increasing the pH value, a base is added. By using a soluble base,
for example, sodium hydroxide. When using a base that is sparingly
soluble, for example, magnesium hydroxide, the latter will hardly
dissolve in water and the aforementioned disadvantages will
occur.
[0006] A further possibility for adjusting a pH value that is
favorable for precipitation is disclosed in DE 101 12 934 B4. The
aeration of primary sludge mentioned therein with subsequent
CO.sub.2 stripping is however very energy-intensive and causes
therefore high additional costs.
[0007] WO 00200101019735 A1 discloses a reactor for removal of
dissolved nitrogen and phosphate from the aqueous portion of liquid
manure by means of electrochemical precipitation.
[0008] The reactor described therein requires relatively high
electrical voltages and is therefore energy-intensive and
cost-intensive. A disadvantage is also that nitrogen and phosphate
that are present organically bound in the aqueous portion of the
liquid manure cannot be removed by the disclosed method. As a
result of this, this wastewater must therefore be subjected to a
subsequent purification in a water treatment plant. The
construction of the reactor is disadvantageous in that, due to the
arrangement of the electrodes, large areas are generated in which
the liquid to be purified has no direct contact with the
electrodes. Moreover, as a result of the geometry of the
sacrificial anode more magnesium than required is released. Both
effects reduce the efficiency of the reactor significantly.
Moreover, in this method, due to the use of aluminum-containing
electrodes, the plant poison aluminum ends up in the precipitation
product. When this product is applied to the soil, the aluminum can
be released and the plant growth can be affected negatively.
[0009] An electrochemical precipitation reactor for MAP is
disclosed in WO 2007/009749 A1. The reactor is however not suitable
for the precipitation of other phosphate salts. Also, the
construction of the reactor does not allow for automatic separation
between purified wastewater and precipitated MAP so that it is
necessary to arranged downstream of the reactor a further apparatus
for solid/liquid separation. Also, a significantly higher apparatus
expenditure is required because, as a result of the construction,
the housing of the reactor cannot be operated as a cathode. In
addition, the magnesium is dissolved non-uniformly because, due to
the spatial arrangement of the electrodes in the reactor, only one
side of the anode is participating in the reaction.
[0010] The invention has the object to provide a reactor by means
of which phosphate-containing wastewater can be treated and
supplied to a further use. Moreover, the invention has the object
to provide a reactor for recovery of phosphate salts as plant
adjuvants which overcomes the aforementioned disadvantages of the
prior art.
[0011] The object is solved according to the invention by a reactor
with a housing. At the center of the housing a sacrificial anode of
magnesium or a magnesium-containing material is arranged. An inert
cathode is arranged concentrically about the sacrificial anode. In
this way, the arrangement of the electrodes in accordance with the
invention provides for a best possible control of the release of
magnesium ions. Since the spacing between magnesium anode and
cathode is kept as minimal as possible, the ions that are required
for the precipitation of the phosphate salts are immediately in
contact with each other and a constantly high concentration of
magnesium ions in the reaction space is ensured. At the same time,
because of the geometry of the sacrificial anode, its surface is
very small so that only little magnesium is spontaneously released.
In this way, advantageously an unnecessary excess of magnesium ions
is prevented.
[0012] By means of the reactor according to the invention, it is
possible by application of a minimal electrical direct current,
smaller than 1 V with current strengths below 1 A, to supply
magnesium ions to the phosphate-containing and ammonium-containing
liquid and to split the water that is contained in the liquid to
OH.sup.- and H.sup.+ ions so that the pH value is increased and the
reactions required for precipitation can take place. Due to the
minimal energy demand, the costs for operating the device drop in
comparison to methods known from the prior art. It is even possible
to operate the reactor by galvanic operation. Electrical current is
produced thereby.
[0013] Moreover, it is proposed that an anaerobic fermentation
process is arranged upstream of the reactor according to the
invention. In this fermentation process nitrogen and phosphorus
that are bound organically are decomposed to inorganic
water-soluble ions. From these ions, ammonium (NH.sub.4.sup.+) and
phosphate (PO.sub.4.sup.3-), the phosphate salts, in particular MAP
and PMP, can be formed. In this way, nitrogen and phosphate that
are bound predominantly to or in organic material or cell mass are
converted advantageously into a water-soluble form and are thus
available for the production of plant adjuvants. Moreover, in this
process biogas is produced which has a significant market value as
an energy source.
[0014] An advantageous embodiment of the invention provides that
the housing is manufactured of an electrically conductive material,
for example, metal and therefore serves as an inert cathode. With
the geometry of the reactor according to the invention and the
concentric arrangement of the sacrificial anode the reaction space
is limited to the space between the two electrodes. In this way,
dead space is avoided and thus material costs are lowered.
[0015] A further advantage of the invention provides that the
sacrificial anode is comprised substantially of magnesium. Of
course, this includes also electrode materials that are comprised
of a magnesium alloy or magnesium with minimal additions of other
components.
[0016] In order to be able to advantageously perform the process of
phosphate salt recovery continuously, the reactor according to the
present invention has an inlet for the phosphate-containing liquid,
an outlet for the purified liquid, as well as a removal device for
the precipitated phosphate salts. The crystals can be removed via
the removal device by means of a shut-off valve, for example, a
seat valve or disk valve or ball valve, from the reactor without
the inlet or outlet being changed and thereby the purification
performance of the reactor being negatively affected.
[0017] An advantageous embodiment of the reactor according to the
invention provides for the operation of the reactor as an upflow
reactor. In this context, the inlet is located laterally at the
bottom end of the reactor. The wastewater flows upward and escapes
laterally at the top. This arrangement has the advantage that an
automatic separation of liquid that flows upwardly and precipitated
salts that sink to the bottom is taking place.
[0018] In principle, the reactor can be operated also as a downflow
reactor wherein the liquid and solid move in the same direction. In
this way, the sedimentation rate of the precipitated phosphate
salts is accelerated. This means that the reactor can be made
smaller for the same throughput.
[0019] In supplementing this, it is proposed that the crystals are
separated in a filter from the liquid. In this way, in the reactor
that is flowed through from top to bottom the precipitated
phosphate salts can be removed together with the liquid from the
reactor. Accordingly, additional fixtures or devices for separate
solids removal are saved. Also, in case of common removal of
phosphate salts and purified wastewater, a turbulent flow is
generated in the conduit and prevents clogging of the conduit by
the crystals.
[0020] It is particularly beneficial when the housing of the
reactor is closed. The electrolytic reactions that occur in the
reactor produce large quantities of foam which in case of a closed
housing cannot overflow. Accordingly, in an advantageous way, a
product loss is avoided. In principle, the housing of the reactor
can also be open partially or entirely.
[0021] The reactor according to the invention operates even better
when it has a slanted bottom. In this way, it is possible that the
precipitated crystals glide along the slanted surface downwardly
and collect at the removal device. In this way, the crystals can be
removed from the reactor without its continuous operation having to
be interrupted. The formation of the slanted surface is realized by
a preferably conical bottom. Conceivable is also the shape of a
pyramid.
[0022] An advantageous embodiment of the reactor according to the
invention provides that to the sacrificial anode a positive pole
and to the cathode a negative pole of a direct current source are
connected. The supply of electrical current prevents deposits on
the electrode which are not stable in the electrical field. When
the reactor, on the other hand, is operated without a direct
current source, we by the process of magnesium release electrons
are released. This means that the reactor requires no electrical
current but even produces electrical current.
[0023] Further advantages and advantageous embodiments of the
invention can be taken from the following Figures, their
description, and the claims. In this context, all features
disclosed in the Figures, their description, and the claims can be
important for the invention individually as well as in any
combination with each other.
[0024] It is shown in:
[0025] FIG. 1 a schematic illustration of the reactor according to
the invention
[0026] FIG. 2 a schematic illustration of a first embodiment of the
reactor according to the invention
[0027] FIG. 3 a schematic illustration of a second embodiment of
the reactor according to the invention
[0028] FIG. 4 a schematic illustration of a third embodiment of the
reactor according to the invention
[0029] FIG. 5 a schematic illustration of a third embodiment of the
reactor according to the invention for recovery of phosphate salts
and
[0030] FIG. 6 a schematic illustration of the use of the reactor
according to the invention with upstream fermentation process
[0031] FIG. 1 shows a schematic illustration of a reactor 10
according to the invention. The reactor 10 has a housing 12. The
housing 12 serves for receiving a phosphate-containing liquid 14.
At the center of the housing 12 an electrode 16 is arranged.
[0032] The electrode 16 is a so-called sacrificial anode which is
connected to the positive pole of a direct current source, not
illustrated in the drawing, while the housing 12 forms the cathode
18 which is connected to a negative pole of the direct current
source.
[0033] The sacrificial anode 16 is comprised of a
magnesium-containing material so that magnesium ions are
transferred into the solution 14 as soon as electrical voltage is
applied to the electrodes 16 and 18.
[0034] Reaction equation for formation of MAP:
Mg.sup.2++NH.sub.4.sup.++PO.sub.4.sup.3-+6
H.sub.2O.fwdarw.MgNH.sub.4PO.sub.4.6 H.sub.2O
[0035] Reaction equation for formation of PMP:
Mg.sup.2++K.sup.++PO.sub.4.sup.3-+6 H.sub.2O.fwdarw.MgKPO.sub.4.6
H.sub.2O
[0036] Reaction equation for release of magnesium:
Mg(s).fwdarw.Mg.sub.2.sup.++2e.sup.-
[0037] Reaction equation for formation of hydroxide ions:
2 H.sub.2O+2e.sup.-.fwdarw.2 OH.sup.-+H.sub.2
[0038] The formed phosphate salts are sparingly soluble in aqueous
solution and precipitate as crystals which deposit at a bottom of
the reactor 10.
[0039] One configuration of the reactor 10 according to the
invention provides for galvanic operation. For this purpose, the
two electrodes 16, 18 are not connected to the external direct
current source. The magnesium ions are transferred into solution by
galvanic operation.
[0040] FIG. 2 shows a first embodiment variant of the reactor 10
according to the invention. Illustrated is the housing 12 of the
reactor and centrally arranged therein is the electrode 16 that is
embodied as a sacrificial anode. Concentric between housing 12 and
electrode 16 there is the cathode 18. In this special arrangement
the spacing between sacrificial anode 16 and inert cathode 18 is
minimal so that the ions that are participating in the
precipitation are immediately in contact with each other.
[0041] In FIG. 3 the reactor 10 is illustrated. Laterally at a
preferably conical bottom 22 there is an inlet 24. An outlet 26 is
located at the top laterally at the housing 12 of the reactor 10.
An optional return line 28 connects the outlet 26 with the inlet
24. At the bottom end of the preferably conical bottom 22 there is
the removal device 30.
[0042] The phosphate-containing liquid 14 flows through the inlet
24 from the bottom to the top through the reactor 10 and exits from
it through the outlet 26. The precipitated phosphate salts glide
along the slanted plane of the conical bottom 22 in downward
direction and are removed via the removal device 30. In this way,
the reactor 10 can be operated continuously and the precipitated
and deposited crystals can be removed at any time without changing
a throughput of the reactor. By means of the optional return line
28, already purified liquid 14 is returned to the reactor 10 as
circulating water.
[0043] FIG. 4 shows a third embodiment of the reactor 10 according
to the invention. Here, the reactor 10 is flowed through in
downward direction. The inlet 24 is located laterally at the top on
the housing 12. The outlet 26 is located laterally at the conical
bottom 22. The optional return line 28 connects the outlet 26 with
the inlet 24. At the conical bottom 22 the removal device 30 is
arranged.
[0044] The phosphate-containing liquid 14 flows through the inlet
24 from the top to the bottom through the reactor 10 and exits from
it through the outlet 26. Precipitated phosphate salts are removed
via the removal device 30 without affecting the operation of the
reactor. By means of return line 28 the already purified liquid 14
is supplied again to the reactor 10 as circulating water.
[0045] FIG. 5 shows a further embodiment of the reactor 10
according to the invention. In this way, the reactor 10 is flowed
through in downward direction. The inlet 24 is located laterally at
the top at the housing 12. The outlet 26 is located at the bottom
end at the conical bottom 22 and extends from there to a downstream
filter 31. The optional return line 28 connects the outlet 26 with
the inlet 24.
[0046] In this fourth embodiment according to the invention, the
precipitated phosphate salts are removed together with the purified
liquid 14 from the reactor 10. In the downstream filter 31 the
phosphate salts are separated from the liquid 14. In this context
there is the possibility to supply seed crystals to the reactor 10
via the return line 28.
[0047] In FIG. 6, an application of the reactor 10 according to the
invention in connection with producing biogas from
phosphorus-containing wastewater is schematically illustrated.
[0048] A wastewater flow 32 of organic origin is supplied to a
bioreactor 34. Herein, by anaerobic fermentation processes, the
organic carbon compounds that are contained in the solids are
converted into biogas and mineral residual substances. In this
process, ammonium-containing and phosphate-containing process water
36 is produced. Before the process water 36 is supplied through
inlet 24 into the reactor 10, possibly contained solids 40 are
separated in a filter 38. The solids 40 which are retained in the
filter 38 are returned into the bioreactor 34. In the afore
described way, in the reactor 10 according to the invention the
phosphate salts are separated. The ammonium-containing and
phosphate-containing outflow 26 can be returned partially into the
bioreactor 34. In this way, an impairment of the fermentation
process, caused by a high ammonium concentration, is prevented.
* * * * *