CA2025433C - Treatment of water - Google Patents
Treatment of water Download PDFInfo
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- CA2025433C CA2025433C CA 2025433 CA2025433A CA2025433C CA 2025433 C CA2025433 C CA 2025433C CA 2025433 CA2025433 CA 2025433 CA 2025433 A CA2025433 A CA 2025433A CA 2025433 C CA2025433 C CA 2025433C
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Abstract
The invention provides a process for the treatment of water containing dissolved sulphate, selenate, tellurate and/or nitrate anions, together with dissolved calcium cations. Water being treated is passed at a pH of 5,0 - 8,5 through an anaerobic biological water treatment stage wherein microorganisms utilize said anions and reduce their concentration in the water. The water from the anaerobic stage is then passed through a calcium carbonate precipitation stage where calcium carbonate is precipitated from the water at a pH of at least 7,0. Producer gas is fed through an anaerobic biological gas treatment stage wherein the proportion of hydrogen relative to carbon monoxide in the gas is increased and this gas is then fed into the anaerobic water treatment stage to provide a metabolizable energy source for the microorganisms in the anaerobic water treatment stage.
Description
~~~ ~~~~;
THIS INVENTTaN relates to the treatment of water. More particularly, the invention relates to a process for the treatment of water suitable .for the biological remaval of sulphate, selenate, tellurate andjor nitrate anions from water.
According to the invention there is provided a process for the treatment of water containing dissolved anions which are members of the group consisting of sulphate ions, selenate ions, tellurate ions and nitrate ions, together with dissolved calcium cations, the process comprising the steps of:
passing the water at a pH of 5, 0 -- 8, 5 through an anaerobic biological water treatment stage wherein microorganisms utilize said anions and reduce their concentration in the water; and passing the water from the anaerobic stage through a calcium carbonate precipitation stage where calcium carbonate is precipitated from the water at a pH of at least 7,0, the process including the step of feeding producer gas through an anaerobic biological gas treatment stage wherein the proportion of hydrogen~relative to carbon monoxide in the gas is increased, the gas from the anaerobic gas 'treatment stage then being fed iota the anaerobic water treatment stage to provide a metabolizable energy source for the microorganisms in the anaerobic water treatment stage.
By 'anaerobic' is meant that in the anaerobic stage there is no molecular oxygen present.
Typically, the water being treated will be acidic, the method including recirculating at least some of the calcium carbonate precipitated from the precipitation stage into the water being treated, upstream of the anaerobic water treatment stage, to 3o increase the pH of the water, before it enters the anaerobic water treatment stage, to said value of 5,0 ~ 8,5. This pH value is regarded as 'neutral' for the purpose of the invention, and n r) '~ fr r.~ ~-s ii c D
According to the invention there is provided a process for the treatment of water containing dissolved anions which are members of the group consisting of sulphate ions, selenate ions, tellurate ions and nitrate ions, together with dissolved calcium cations, the process comprising the steps of:
passing the water at a pH of 5, 0 -- 8, 5 through an anaerobic biological water treatment stage wherein microorganisms utilize said anions and reduce their concentration in the water; and passing the water from the anaerobic stage through a calcium carbonate precipitation stage where calcium carbonate is precipitated from the water at a pH of at least 7,0, the process including the step of feeding producer gas through an anaerobic biological gas treatment stage wherein the proportion of hydrogen~relative to carbon monoxide in the gas is increased, the gas from the anaerobic gas 'treatment stage then being fed iota the anaerobic water treatment stage to provide a metabolizable energy source for the microorganisms in the anaerobic water treatment stage.
By 'anaerobic' is meant that in the anaerobic stage there is no molecular oxygen present.
Typically, the water being treated will be acidic, the method including recirculating at least some of the calcium carbonate precipitated from the precipitation stage into the water being treated, upstream of the anaerobic water treatment stage, to 3o increase the pH of the water, before it enters the anaerobic water treatment stage, to said value of 5,0 ~ 8,5. This pH value is regarded as 'neutral' for the purpose of the invention, and n r) '~ fr r.~ ~-s ii c D
the pH in the anaerobic stage is preferably 6,5 - 7,5. If insufficient calcium carbonate is precipitated for this purpose, calcium hydraxide may also be added to the water being treated upstream of the anaerobic water treatment stage. This calcium carbonate and calcium hydroxide may be added to the water upstream, relative to water flow, of a neutralization stage such as a stirred tank located upstream o.f the anaerobic water treatment stage.
Calcium carbonate precipitation in the precipitation stage should take place at a pH of about 7,0 - 9,0, eg about 8,0. If the pH
of the water leaving the anaerobic water treatment stage is too low, calcium hydroxide may be added thereto, upstream of the precipitation stage, to increase the pH to a desired value.
A propartion of the treated water, issuing from the precipitation stage, may be fed to the anaerobic gas treatment stage, as water make--up; and if the concentration of anions to be removed from the feed water is too high [above eg 2000 mg/1] and there is a danger of calcium sulphate precipitation, a proportion of the treated water from the precipitation stage may be added to the water being treated, eg upstream of the neutralization stage.
When the water being treated contains sulphate ions, hydrogen sulphide will be produced in the anaerobic water treatment stage, and the process comprising the step of passing water issuing from the anaerobic water treatment stage through a hydrogen sulphide removal stage before it passes on to the precipitation stage.
The process can in principle be carried out batchwise, but is preferably carried out continuously.
When the water being treated contains ions selected from the group consisting of selenate ions and tellurate ions [the Se(VI) and Te(VT) ions respectively] the water will usually alsa contain sulphates, and the Se(VI) and Te(VI) ions will be reduced biologically in the anaerobic stage [which will act as a :.~ ! . G .,V,b biological sulphate removal stage] to the corresponding Se(IV) and Te(IV) ions which then reack: with the hydrogen sulphide and precipitate as insoluble selenium sulphides and tellurium sulphides; and/or said Se(VI) and Te(VI) ions may be reduced to the corresponding Se(TI) and Te(II) ions, which react with heavy metals and precipitate respectively as heavy metal selenides and tellurides, and/or Se(VI) and Te(VI) ions may be reduced to the corresponding Se and Te metallic states. This will happen automatically when there are sufficient sulphate ions in the raw water to be treated, but if there are not, and the raw water being treated contains chalcogenate ions other than sulphate ions, the process may include the step of adding sulphate ions to the water being treated. Thus, optionally, the invention contemplates an embodiment of the process in which the water 25 being treated contains selenate ions and/or tellurate ions as the Se(VI) and Te(VI) ions respectively, the process including the step of adding sulphate ions to the water upstream of the anaerobic sulphate removal stage.
Naturally, when sulphate ions are added to the water upstream of the anaerobic sulphate remaval stage, the water may be neutralized if necessary, the addition of such sulphate ions acting to ensure that sufficient hydrogen sulphide is released in the anaerobic sulphate removal stage for the precipitation of the sulphides of Se(IV) and Te(IV). The various refinements of the process described herein when the process is used primarily for the removal of sulphates of the water are in principle also possible when the primary purpose of the invention is the removal of selenates and tellurates from the raw water, in analogous fashion, although the object of the process may primarily be far the removal of selenates and/or tellurates from raw water, rather than the removal of sulphates.
The hydrogen sulphide removal stage may be a gas stripping stage in which hydrogen sulphide is stripped, eg by means of steam, nitrogen or carbon dioxide, from the water in a packed tower.
This is to prevent hydrogen sulphide dissolved in water passing w c i'y r~
l.4r ;~,j e.~
from the anaerobic sulphate removal stage from subsequently being oxidized back to sulphate ions when exposed to oxygen, eg when exposed to the environment. The packed tower may be packed eg with plastics or ceramic artifacts such as rings or the like, and 5 the hydrogen sulphide gas so obtained can then act as a raw material for further processing to produce sulphur. Naturally, vacuum stripping or other suitable stripping processes may be employed.
Naturally, where sulphur production is not important, the hydrogen sulphide may merely be allowed to escape from the water leaving the anaerobic sulphate removal stage, before said water reaches the precipitation stage.
~lny excess calcium carbonate removed from the precipitation stage can be converted to lime and carbon dioxide by-products, eg by calcining. Hydrogen sulphide removed from the hydrogen sulphide removal stage may be converted to sulphur as a by-product. This conversion may be any well known conventional process such as the Clauss process, the Stretford process or the biological Cork process.
hurthermore it will be appreciated that, instead of producing sulphur as a by-product, the process may optionally produce, as a by-product, eg hydrogen sulphide, sodium sulphide, sodium hydrogen sulphide, or calcium sulphide, as desired.
The hydrogen sulphide stripping (when air is used from the stripping), may take place in a plurality of successive separate stages to which carbon dioxide is added so that they are at successively decreasing pH's, down to a final pH of preferably not less than 6, thereby to minimize calcium bicarbonate production.
Tha_ microorganisms which utilize the sulphate ions may comprise at least one species selected from the group comprising:
Desulphovibrio desulphuricans Hd , 3 :_ e_3 e.~
Calcium carbonate precipitation in the precipitation stage should take place at a pH of about 7,0 - 9,0, eg about 8,0. If the pH
of the water leaving the anaerobic water treatment stage is too low, calcium hydroxide may be added thereto, upstream of the precipitation stage, to increase the pH to a desired value.
A propartion of the treated water, issuing from the precipitation stage, may be fed to the anaerobic gas treatment stage, as water make--up; and if the concentration of anions to be removed from the feed water is too high [above eg 2000 mg/1] and there is a danger of calcium sulphate precipitation, a proportion of the treated water from the precipitation stage may be added to the water being treated, eg upstream of the neutralization stage.
When the water being treated contains sulphate ions, hydrogen sulphide will be produced in the anaerobic water treatment stage, and the process comprising the step of passing water issuing from the anaerobic water treatment stage through a hydrogen sulphide removal stage before it passes on to the precipitation stage.
The process can in principle be carried out batchwise, but is preferably carried out continuously.
When the water being treated contains ions selected from the group consisting of selenate ions and tellurate ions [the Se(VI) and Te(VT) ions respectively] the water will usually alsa contain sulphates, and the Se(VI) and Te(VI) ions will be reduced biologically in the anaerobic stage [which will act as a :.~ ! . G .,V,b biological sulphate removal stage] to the corresponding Se(IV) and Te(IV) ions which then reack: with the hydrogen sulphide and precipitate as insoluble selenium sulphides and tellurium sulphides; and/or said Se(VI) and Te(VI) ions may be reduced to the corresponding Se(TI) and Te(II) ions, which react with heavy metals and precipitate respectively as heavy metal selenides and tellurides, and/or Se(VI) and Te(VI) ions may be reduced to the corresponding Se and Te metallic states. This will happen automatically when there are sufficient sulphate ions in the raw water to be treated, but if there are not, and the raw water being treated contains chalcogenate ions other than sulphate ions, the process may include the step of adding sulphate ions to the water being treated. Thus, optionally, the invention contemplates an embodiment of the process in which the water 25 being treated contains selenate ions and/or tellurate ions as the Se(VI) and Te(VI) ions respectively, the process including the step of adding sulphate ions to the water upstream of the anaerobic sulphate removal stage.
Naturally, when sulphate ions are added to the water upstream of the anaerobic sulphate remaval stage, the water may be neutralized if necessary, the addition of such sulphate ions acting to ensure that sufficient hydrogen sulphide is released in the anaerobic sulphate removal stage for the precipitation of the sulphides of Se(IV) and Te(IV). The various refinements of the process described herein when the process is used primarily for the removal of sulphates of the water are in principle also possible when the primary purpose of the invention is the removal of selenates and tellurates from the raw water, in analogous fashion, although the object of the process may primarily be far the removal of selenates and/or tellurates from raw water, rather than the removal of sulphates.
The hydrogen sulphide removal stage may be a gas stripping stage in which hydrogen sulphide is stripped, eg by means of steam, nitrogen or carbon dioxide, from the water in a packed tower.
This is to prevent hydrogen sulphide dissolved in water passing w c i'y r~
l.4r ;~,j e.~
from the anaerobic sulphate removal stage from subsequently being oxidized back to sulphate ions when exposed to oxygen, eg when exposed to the environment. The packed tower may be packed eg with plastics or ceramic artifacts such as rings or the like, and 5 the hydrogen sulphide gas so obtained can then act as a raw material for further processing to produce sulphur. Naturally, vacuum stripping or other suitable stripping processes may be employed.
Naturally, where sulphur production is not important, the hydrogen sulphide may merely be allowed to escape from the water leaving the anaerobic sulphate removal stage, before said water reaches the precipitation stage.
~lny excess calcium carbonate removed from the precipitation stage can be converted to lime and carbon dioxide by-products, eg by calcining. Hydrogen sulphide removed from the hydrogen sulphide removal stage may be converted to sulphur as a by-product. This conversion may be any well known conventional process such as the Clauss process, the Stretford process or the biological Cork process.
hurthermore it will be appreciated that, instead of producing sulphur as a by-product, the process may optionally produce, as a by-product, eg hydrogen sulphide, sodium sulphide, sodium hydrogen sulphide, or calcium sulphide, as desired.
The hydrogen sulphide stripping (when air is used from the stripping), may take place in a plurality of successive separate stages to which carbon dioxide is added so that they are at successively decreasing pH's, down to a final pH of preferably not less than 6, thereby to minimize calcium bicarbonate production.
Tha_ microorganisms which utilize the sulphate ions may comprise at least one species selected from the group comprising:
Desulphovibrio desulphuricans Hd , 3 :_ e_3 e.~
Desul~hovibrio vulaaris Desulphovibrio salexic~ens Desul~hovibrio i as Desulphovibrio africanus Desul~homaculum niarificans Desulphomaculum ruminis Desulphomaculum oriemtis These microorganisms, of which Desulphovibrio desul~huricans is a typical example, are capable, in the presence of a suitable source of metabolizable carbon and under anaerobic conditions, of metabolizing sulphate ions with the production of hydrogen sulphide. Such microorganisms may initially be seeded into the sulphate removal stage from a cultivated source as a more or less pure strain of microorganisms, or, as they are typically present as part of a plurality of mixed species of microorganisms in various natural sources such as sewage, a. suitable natural source of mixed microorganisms may be introduced into the sulphate removal stage where the process conditions will result in proliferation, at the expense of other microorganisms, of desirable microorganisms capable of growth and cell division in the anaerobic environment, ie those, such as Desulphovirbio desulphuricans, which are capable of utilizing the sulphates in the water.
The process of the present invention is suitable for the treatment of lime-neutralized mine waters, such as are pumped as effluent waters from gold mines, which contain dissolved calcium ions, and the process is also suitable for sulphate ion-containing effluent waters from gold mine ore processing or other industrial sources, which do not necessarily~contain dissolved calcium ions. When such effluent waters are acceptably neutral as regards pH, they can be treated directly in accordance with the process of the present invention, but if not, the process will typically include the preliminary step of neutralizing them eg by means of calcium hydroxide or recirculating calcium carbonate, as described above.
J ~,~ e,v .
The process of the present invention is suitable for the treatment of lime-neutralized mine waters, such as are pumped as effluent waters from gold mines, which contain dissolved calcium ions, and the process is also suitable for sulphate ion-containing effluent waters from gold mine ore processing or other industrial sources, which do not necessarily~contain dissolved calcium ions. When such effluent waters are acceptably neutral as regards pH, they can be treated directly in accordance with the process of the present invention, but if not, the process will typically include the preliminary step of neutralizing them eg by means of calcium hydroxide or recirculating calcium carbonate, as described above.
J ~,~ e,v .
The anaerobic sulphate removal stage may be provided by one or more anaerobic reactors in series, such as packed bed reactors, sludge blanket reactors, fluidized bed reactors, rotating disc reactors, or the like, followed eg by the aforesaid hydrogen sulphide stripping stage. As regards the anaerobic sulphate removal stage, it should be noted that the cations of heavy metals such as silver, lead or the like, will form sulphides by reaction with the hydrogen sulphide produced in said stage, and these heavy metal sulphides will be in the form of precipitates which can be removed as solids from the anaerobic sulphate removal stage.
Suitable process conditions for operating the anaerobic stages are the absence of molecular oxygen, a pH of 5 - 8,5, a temperature of 5 - 85°C, eg 10-40°C and a chemical oxygen demand [COD] of not less then 50 mg/l.
When any heavy metal in the raw water can form a valuable by-product, the water being treated may be passed through a heavy metal recovery stage prior to any biological treatment thereof, hydrogen sulphide from the hydrogen sulphide removal stage being fed into the heavy metal recovery stage to precipitate heavy metal as sulphide from the water. Removing heavy metals from the water prior to passing the water through the anaerobic stage, can facilitate recovery of the heavy metal sulphides as by-products.
Instead of or in addition to being used to remove sulphate, selenate and/or tellurate ions from the water being treated, the process may be used to remove nitxate ions therefrom.
In this case, the anaerobic biological water treatment stage will act as a denitrification stage and will contain microorganisms capable of utilizing nitrate and optionally nitrite ions. This biological denitrification renders the process of the invention suitable for the purification of water which, instead of sulphate, selenate or tellurate ions, contains nitrate and/or nitrite ions. By suitable control of the process conditions in r < r' ~' ~ ~ r~s .a l::,T zj s~
it/ 1-d .
g the denitrification stage, eg the absence of molecular oxygen, a pH of 5 - 8,5, a temperature of 5 - 85°C, eg 5-~0°C and a chemical oxygen demand of not less than 50 mg/1, said microorganisms capable of utilizing nitrate ions can, in 'the presence of said metabolizable carbon source, effect a biological denitrification, with the production of gaseous nitrogen compounds and carbon dioxide. This embodiment the invention contemplates the step of seeding the anoxic stage with microorganisms capable of biological denitrification, either from a selected strain, or from a mixed population of microorganisms as may be obtained from sewage or the like, the microorganisms capable of biological denitrification proliferating, at the expense of other microorganisms, in the anoxic stage.
Accordingly, in this optional embodiment of the process, the water being treated contains nitrate ions, said water being subjected to a denitrification in the anaerobic biological water treatment stage, the anaerobic biological water treatment stage containing microorganisms capable of utilizing nitrate ions (and optionally nitrite ions), and comprising at least one species selected from the group consisting ofo Achromabacter sip. Enterobacter spp.
Aerobacter spp. Citrobacter s~ax~.
Alcaliqenes spp. Pebtococcus spp~
Bacillus spp. Propianibacterium spp.
Flavobacterium spp.
Micrococcus sp .
Proteus sp~g-Pseudomonas spo.
In the anaerobic gas treatment stage suitable microorganisms utilize Co in the producer gas, thereby increasing the proportion of H2 relative to CO therein. Microarganisms can also utilize H2, C02 and Co to produce by-products in the form of short-chain liquid petroleum gas-type hydrocarbons such as CH4, short-chain carboxylic acids such as CH3oH and snort-chain alcohols such as CH30H, while water is consumed. 'Water make-up, as mentioned above, is added to the anaerobic gas treatment stage in the form I ~ ~ '~ ''' ~' '' ~'lyGe5 of water rec:irculated from the precipitation stage. The gas passing through the gas treatment stage is fed ~to the anaerobic water treatment stage where the H2 and CO 'therein, and any said hydrocarbons, acids and alcohols as are carried over thereby from the gas treatment stage, are used as energy sources for the microorganisms in the anaerobic water treatment stage.
Similarly, suitable microorganisms for the gas treatment stage may be obtained from a mixed source such as sewage, and proliferate at the expense of other organisms in the gas :10 treatment stage, or a suitable selected strain or strains may be introduced into the gas treatment stage. Thus, microorganisms comprising at least one species, selected from the group consisting of:
o Rhodopseudomonas spp. Bwt~ribacterium spp.
S~aromusa sgp. Clostridium spp.
Acetobacterium s~~. Desulphovibrio desulphuricans may be utilized in the anaerobic gas treatment stage to increase the propartion of said hydrogen relative to said carbon monoxide, In the anaerobic gas treatment stage the microorganisms in question can produce fatty acids such as acetic acid, propionic acid and/or butyric acid, and the pracess may include the step of withdrawing water from the anaerobic gas treatment stage and recovering one or more of fatty acids from this water as a by-product.
The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing in which the single figure shows a schematic flow diagram of a multipurpose installation in accordance with the present invention, for carrying out the various aspects of the process of the present invention.
In the drawings, reference numeral 10 generally designates a water treatment installation suitable for carrying out various aspects of the process of the present invention. Naturally, other installations, differing somewhat in layout, can be employed.
The installation 10 comprises a raw water feed flow line 12 feeding into a neutralization stage 14 in the form of a stirred tank, from the neutralization stage 14 a water flow line 16 leads to an anaerobic water treatment stage 18. The stage 18 is provided by one or more reactors arranged in series, typically packed bed reactors, fluidized bed reactors, so-called pelleted or granular reactors, completely mixed reactors or rotating disc units. The stage 18 has a solids outlet flow line 21. Packed bed reactors and fluidized bed reactors, when used, may contain dolomitic 'gravel, power station fly ash, activated carbon and activated charcoal, plastics or ceramic artifacts such as rings or the like, and one or more of the reactors may be provided with settling tanks, if required.
The anaerobic stage 18 feeds via a flow line 20 to a sulphide removal stage, generally designated 22, which acts as a gas stripping stage. In the stripping stage 22 a plurality of stripping towers are arranged in series in the direction of water flow, two of which towers are shown. The towers are designated 24 and are interconnected in series by a plurality of water flow lines 2G. Each tower 24 has a stripped gas outlet flow line 28, the flow lines 28 joining a common stripped gas flow line 30 which leads to a sulphur production stage 32 having a sulphur product cutlet flow line 34. If granular calcium carbonate packing material is used in the towers 24, then this can assist in calcium carbonate precipitation in the calcium carbonate precipitation stage (44 described hereunder).
Each tower 24 in turn has a calcium carbonate outlet flaw line 36, the flow lines 36 joining a common calcium carbonate flow line 38. Each tower 24 further has a strapping gas feed flow line 40, each flow line 40 being connected to a common supply of C02 and to a common supply of air in a fashion such that Co2 and/or ~i ~ ~ ~~~.~ z:
air from the respective supplies may selectively be fed therealong.
A treated water flow line 42 leads from the stripping stage 22 to a calcium carbonate precipitation stage 44. The precipitation stage 44 is in the form of a settling 'tank and it has a clean water product flow line 46 issuing therefrom, and a calcium carbonate precipitate outlet flow line 48 issuing therefrom.
The flow line 38 leads into the flow line 48, and the flow line 48 has a branch line 50 leading therefrom into the raw water feed line 12, upstream of the neutralization stage 14. The clean water product line 46 in turn has a branch flow line 52 leading therefrom, arid also feeding into the flow line 12, upstream of the neutralization stage.
A biological anaerobic gas treatment stage 54, typically a reactor similar to those of the stage 18, is provided with a producer gas feed flow line 56, and feeds via a gas outlet flow line 58 into the stage 18. A water make-up flow line 60 leads from the flow line 52 into the stage 54.
Calcium hydroxide feed lines 62 and 64 are shown feeding respectively into flow lines 12 and 42.
When the water treatment process of the present invention is used primarily for the removal of sulphate ions from a raw water feed, biological sulphate ion removal takes place in the stage 18. Such raw waters are typically more acidic than pH 5,0 so that sufficient calcium carbonate is added thereto in feed line 12 via flow line 50, to reduce the pI3 to a suitable value of at least 5 and preferably 6,5 -7,5. If the calcium carbonate available along flow line 50 is insufficient for this neutralization, a suitable base, ideally calcium hydroxide, is added to the flaw line 12 via flow line 62.
~~~y~~:~,~;
,, .u =; :,r Furthermore if 'the sulphate ion concentration in the raw water is too high, say above 2000 mg/1, this feed water may be diluted by water from flow line 52, fed into flow line 12.
Any calcium carbonate, water and calcium hydroxide fed respectively via flow lines 50, 52 and 62 into flow line 12 is mixed with the raw water in flow line 12, in 'the neutralization stage 14.
In the anaerobic stage 18 biological sulphate ion removal takes plane by virtue of the growth of sulphate ion-consuming microorganisms such as Desulphovibrio desulphuricans therein.
These are initially introduced as a suitable selected strain or from a mixed source, and in the environment of the stage 18 they proliferate to the exclusion of other microorganisms.
At the same time producer gas, containing H2 and CO, is fed along flow line 56 into stage 54. In the anaerobic conditions in stage 54 microorganisms suspended in water consume H2, CO and C02, producing short chain hydrocarbons, carboxylic fatty acids and alcohols, and increasing the ratio of F-T2 to CO in the gas. Gas, containing said H2, CO, and possibly some hydrocarbons, acids and alcohols, leaves 'the stage 54 to enter the stage 18 via flow line 58. Water consumed in stage 54 by the microorganisms and/or carried ovex into stage 18 in the gas flow along flow line 58, is made up by water fed into stage 54 from flow line 50 via flow line 60.
Process water passes on from the anaerobic stage 18 along flow line 20 to the stripping stage 22. In the stripping stage 22 a mixture of air and carbon dioxide is fed into each stripping tower 24 along its associated flow line 40. The carbon dioxide reduces the pH of the water in the towers to a desired value, in the range of 8 to 5, there being a successive reduction of pH
from one tower 24 to the next in the direction of process water flow. In each tower 24 the carbon dioxide in the stripping gas reacts with dissolved calcium sulphide in the process water to a 'j ~J t.% ~:_ Cl ~i produce hydrogen sulphide which is stripped from the tower as gas, which leaves the tower along the associated flow line 28.
Stripped gas from the flow lines 2$ enters the flow line 30 and then the sulphur production stage 32. In the sulphur production stage a suitable process such as the Clauss or Stretford process may be used to produce sulphur, eg by oxidation of the hydrogen sulphide employing ferric ions to produce sulphur and ferrous ions. Sulphur product issues from the stage 32 along flow line 34.
Product water leaves the stripping stage 22 along the flow line 42 and there is sufficient calcium hydroxide addition thereto along flow line 64 to reduce its pH to about 8. It is fed into the seder 44 for calcium carbonate crystals therein to settle.
Residual calcium carbonate crystals in the process water are settled in the stage 44 and issue from the stage 44 along flow line 48, as a by-product. Calcium carbonate produced in the towers 24 and issuing therefrom along flow lines 36 passes along flow line 38 into the calcium carbonate product flow line 48.
Calcium carbonate flow line 50, which feeds calcium carbonate into the flow line 12 as described above, branches from the flow line 48.
Finally, treated process water product issues .from precipitation stage 44 along flow line 46, from which it can be discharged into the environment. The flow line 52, which feeds water into the flow line 12 and which via flow line 60 feeds water into the anaerobic gas treatment stage 54, branches from the flow line 46.
Any selenates and/or tellurates in the raw water will be reduced biologically in 'the stage 18 from the respective Se(VI) and Te(VI) ions to the corresponding Se(IV) and Te(IV) ions, which in turn react with hydrogen sulphide in the stage 18 and precipitate as insoluble selenium and tellurium sulphides, which issue from the stage 18, together with sludge from stage 28, via flow line 21. If desired, a proportion of the sludge flowing rJ ~.~1 G :~
along flow line 21 can be recycled into the stage 18, to maintain a suitable solids content in the stage 18.
If the raw water being treated primarily contains selenate and tellurate ions, and not sulphate ions, then the process contemplates the possibility of adding some sulphate ions to the raw water in the flow line 12 upstream of the neutralization stage 14, eg as calcium sulphate, to enable selenate and tellurate ions to be removed from the water as described above.
Turning now to the embodiment of the present invention whereby nitrate ions are removed from the raw water which is treated, instead of sulphate ions, the main difference in the installatian is that the hydrogen sulphide stripping stage 22 is no longer required, and can be omitted in its entirety, including the stage 32, and the associated flow lines 28, 30 and 34, and the flow lines 36, 38 and 40.
In accordance with this embodiment of the process, the raw feed water contains dissolved nitrate and/or nitrite ions, and is typically more acidic than pH 5. Thus, tree fundamental difference between nitrate removal and sulphate/selenate/ tellurate removal is that in nitrate removal the anaerobic water treatment stage 18 does not act as a sulphate removal stage, but acts as a biological denitrification stage where nitrate and/or nitrite ions are biologically removed from the water by consumption thereof by suitable microorganisms, leading to the productian of nitrogen gas and carbonate and/or bicarbonate ions.
Once again the stage 18 is operated at a pH of 5 -8,5, preferably 6,5 - 7,5, sufficient calcium carbonate being added to the feed water via flow line 50, optionally with calcium hydroxide addition via flow line 62, to obtain such suitable pH.
In similar fashion, a metabolizable carbon source obtained from producer gas is added, as described above, .from the anaerobic gas treatment stage 54.
~ :y v ~.i e;~
The nitrogen prodvcad by the denitrification is not an 's environmental hazard, and can be discharged together with the product water into the environment, without any gas stripping ' stage.
5 In similar fashion, however, calcium hydroxide is added to the water along flow line 64 into the flow ll.ile 20/42 which leads directly from the stage 18 to the stage 44 so as to obtain a pH
of about 8 in the stage 44, for calcium carbonate precipitation.
Once again, calcium carbonate and water issue from stage 44 along 10 flow lines 48 and 46, together with the above described recirculation respectively of calcium carbonate and water along flow lines 50 and flow lines 52/60.
If desired, fatty acids (eg acetic acid, propionic acid and/or butyric acid) produced in the anaerobic gas treatment stage 54 15 and dissolved in water therein can be recovered as a by-product by withdrawing water from stage 54 via a flow line 66 (broken lines) and separating said fatty acids from this water, eg by concentration, evaporation or the like.
If the HzS concentration in the anaerobic water treatment stage 18 becomes excessively high, this may possibly adversely affect cultivation of microorganisms therein. The invention thus contemplates the possibility of recirculating water from flow line 42 to flow line 16 via a suitable flow line (not shown), to reduce H2S concentration in stage 18.
It is an advantage of the invention that it provides a versatile and flexible multi-purpose water treatment process, suitable for the removal of sulphate, selenate, tellurate, and/or nitrate ions from a raw water feed. Hydrogen sulphide [which can be converted to sulphur or other sulphur-containing materials] and calcium carbonate [which can be converted to lime and carbon dioxide] are produced as by-products.
Suitable process conditions for operating the anaerobic stages are the absence of molecular oxygen, a pH of 5 - 8,5, a temperature of 5 - 85°C, eg 10-40°C and a chemical oxygen demand [COD] of not less then 50 mg/l.
When any heavy metal in the raw water can form a valuable by-product, the water being treated may be passed through a heavy metal recovery stage prior to any biological treatment thereof, hydrogen sulphide from the hydrogen sulphide removal stage being fed into the heavy metal recovery stage to precipitate heavy metal as sulphide from the water. Removing heavy metals from the water prior to passing the water through the anaerobic stage, can facilitate recovery of the heavy metal sulphides as by-products.
Instead of or in addition to being used to remove sulphate, selenate and/or tellurate ions from the water being treated, the process may be used to remove nitxate ions therefrom.
In this case, the anaerobic biological water treatment stage will act as a denitrification stage and will contain microorganisms capable of utilizing nitrate and optionally nitrite ions. This biological denitrification renders the process of the invention suitable for the purification of water which, instead of sulphate, selenate or tellurate ions, contains nitrate and/or nitrite ions. By suitable control of the process conditions in r < r' ~' ~ ~ r~s .a l::,T zj s~
it/ 1-d .
g the denitrification stage, eg the absence of molecular oxygen, a pH of 5 - 8,5, a temperature of 5 - 85°C, eg 5-~0°C and a chemical oxygen demand of not less than 50 mg/1, said microorganisms capable of utilizing nitrate ions can, in 'the presence of said metabolizable carbon source, effect a biological denitrification, with the production of gaseous nitrogen compounds and carbon dioxide. This embodiment the invention contemplates the step of seeding the anoxic stage with microorganisms capable of biological denitrification, either from a selected strain, or from a mixed population of microorganisms as may be obtained from sewage or the like, the microorganisms capable of biological denitrification proliferating, at the expense of other microorganisms, in the anoxic stage.
Accordingly, in this optional embodiment of the process, the water being treated contains nitrate ions, said water being subjected to a denitrification in the anaerobic biological water treatment stage, the anaerobic biological water treatment stage containing microorganisms capable of utilizing nitrate ions (and optionally nitrite ions), and comprising at least one species selected from the group consisting ofo Achromabacter sip. Enterobacter spp.
Aerobacter spp. Citrobacter s~ax~.
Alcaliqenes spp. Pebtococcus spp~
Bacillus spp. Propianibacterium spp.
Flavobacterium spp.
Micrococcus sp .
Proteus sp~g-Pseudomonas spo.
In the anaerobic gas treatment stage suitable microorganisms utilize Co in the producer gas, thereby increasing the proportion of H2 relative to CO therein. Microarganisms can also utilize H2, C02 and Co to produce by-products in the form of short-chain liquid petroleum gas-type hydrocarbons such as CH4, short-chain carboxylic acids such as CH3oH and snort-chain alcohols such as CH30H, while water is consumed. 'Water make-up, as mentioned above, is added to the anaerobic gas treatment stage in the form I ~ ~ '~ ''' ~' '' ~'lyGe5 of water rec:irculated from the precipitation stage. The gas passing through the gas treatment stage is fed ~to the anaerobic water treatment stage where the H2 and CO 'therein, and any said hydrocarbons, acids and alcohols as are carried over thereby from the gas treatment stage, are used as energy sources for the microorganisms in the anaerobic water treatment stage.
Similarly, suitable microorganisms for the gas treatment stage may be obtained from a mixed source such as sewage, and proliferate at the expense of other organisms in the gas :10 treatment stage, or a suitable selected strain or strains may be introduced into the gas treatment stage. Thus, microorganisms comprising at least one species, selected from the group consisting of:
o Rhodopseudomonas spp. Bwt~ribacterium spp.
S~aromusa sgp. Clostridium spp.
Acetobacterium s~~. Desulphovibrio desulphuricans may be utilized in the anaerobic gas treatment stage to increase the propartion of said hydrogen relative to said carbon monoxide, In the anaerobic gas treatment stage the microorganisms in question can produce fatty acids such as acetic acid, propionic acid and/or butyric acid, and the pracess may include the step of withdrawing water from the anaerobic gas treatment stage and recovering one or more of fatty acids from this water as a by-product.
The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing in which the single figure shows a schematic flow diagram of a multipurpose installation in accordance with the present invention, for carrying out the various aspects of the process of the present invention.
In the drawings, reference numeral 10 generally designates a water treatment installation suitable for carrying out various aspects of the process of the present invention. Naturally, other installations, differing somewhat in layout, can be employed.
The installation 10 comprises a raw water feed flow line 12 feeding into a neutralization stage 14 in the form of a stirred tank, from the neutralization stage 14 a water flow line 16 leads to an anaerobic water treatment stage 18. The stage 18 is provided by one or more reactors arranged in series, typically packed bed reactors, fluidized bed reactors, so-called pelleted or granular reactors, completely mixed reactors or rotating disc units. The stage 18 has a solids outlet flow line 21. Packed bed reactors and fluidized bed reactors, when used, may contain dolomitic 'gravel, power station fly ash, activated carbon and activated charcoal, plastics or ceramic artifacts such as rings or the like, and one or more of the reactors may be provided with settling tanks, if required.
The anaerobic stage 18 feeds via a flow line 20 to a sulphide removal stage, generally designated 22, which acts as a gas stripping stage. In the stripping stage 22 a plurality of stripping towers are arranged in series in the direction of water flow, two of which towers are shown. The towers are designated 24 and are interconnected in series by a plurality of water flow lines 2G. Each tower 24 has a stripped gas outlet flow line 28, the flow lines 28 joining a common stripped gas flow line 30 which leads to a sulphur production stage 32 having a sulphur product cutlet flow line 34. If granular calcium carbonate packing material is used in the towers 24, then this can assist in calcium carbonate precipitation in the calcium carbonate precipitation stage (44 described hereunder).
Each tower 24 in turn has a calcium carbonate outlet flaw line 36, the flow lines 36 joining a common calcium carbonate flow line 38. Each tower 24 further has a strapping gas feed flow line 40, each flow line 40 being connected to a common supply of C02 and to a common supply of air in a fashion such that Co2 and/or ~i ~ ~ ~~~.~ z:
air from the respective supplies may selectively be fed therealong.
A treated water flow line 42 leads from the stripping stage 22 to a calcium carbonate precipitation stage 44. The precipitation stage 44 is in the form of a settling 'tank and it has a clean water product flow line 46 issuing therefrom, and a calcium carbonate precipitate outlet flow line 48 issuing therefrom.
The flow line 38 leads into the flow line 48, and the flow line 48 has a branch line 50 leading therefrom into the raw water feed line 12, upstream of the neutralization stage 14. The clean water product line 46 in turn has a branch flow line 52 leading therefrom, arid also feeding into the flow line 12, upstream of the neutralization stage.
A biological anaerobic gas treatment stage 54, typically a reactor similar to those of the stage 18, is provided with a producer gas feed flow line 56, and feeds via a gas outlet flow line 58 into the stage 18. A water make-up flow line 60 leads from the flow line 52 into the stage 54.
Calcium hydroxide feed lines 62 and 64 are shown feeding respectively into flow lines 12 and 42.
When the water treatment process of the present invention is used primarily for the removal of sulphate ions from a raw water feed, biological sulphate ion removal takes place in the stage 18. Such raw waters are typically more acidic than pH 5,0 so that sufficient calcium carbonate is added thereto in feed line 12 via flow line 50, to reduce the pI3 to a suitable value of at least 5 and preferably 6,5 -7,5. If the calcium carbonate available along flow line 50 is insufficient for this neutralization, a suitable base, ideally calcium hydroxide, is added to the flaw line 12 via flow line 62.
~~~y~~:~,~;
,, .u =; :,r Furthermore if 'the sulphate ion concentration in the raw water is too high, say above 2000 mg/1, this feed water may be diluted by water from flow line 52, fed into flow line 12.
Any calcium carbonate, water and calcium hydroxide fed respectively via flow lines 50, 52 and 62 into flow line 12 is mixed with the raw water in flow line 12, in 'the neutralization stage 14.
In the anaerobic stage 18 biological sulphate ion removal takes plane by virtue of the growth of sulphate ion-consuming microorganisms such as Desulphovibrio desulphuricans therein.
These are initially introduced as a suitable selected strain or from a mixed source, and in the environment of the stage 18 they proliferate to the exclusion of other microorganisms.
At the same time producer gas, containing H2 and CO, is fed along flow line 56 into stage 54. In the anaerobic conditions in stage 54 microorganisms suspended in water consume H2, CO and C02, producing short chain hydrocarbons, carboxylic fatty acids and alcohols, and increasing the ratio of F-T2 to CO in the gas. Gas, containing said H2, CO, and possibly some hydrocarbons, acids and alcohols, leaves 'the stage 54 to enter the stage 18 via flow line 58. Water consumed in stage 54 by the microorganisms and/or carried ovex into stage 18 in the gas flow along flow line 58, is made up by water fed into stage 54 from flow line 50 via flow line 60.
Process water passes on from the anaerobic stage 18 along flow line 20 to the stripping stage 22. In the stripping stage 22 a mixture of air and carbon dioxide is fed into each stripping tower 24 along its associated flow line 40. The carbon dioxide reduces the pH of the water in the towers to a desired value, in the range of 8 to 5, there being a successive reduction of pH
from one tower 24 to the next in the direction of process water flow. In each tower 24 the carbon dioxide in the stripping gas reacts with dissolved calcium sulphide in the process water to a 'j ~J t.% ~:_ Cl ~i produce hydrogen sulphide which is stripped from the tower as gas, which leaves the tower along the associated flow line 28.
Stripped gas from the flow lines 2$ enters the flow line 30 and then the sulphur production stage 32. In the sulphur production stage a suitable process such as the Clauss or Stretford process may be used to produce sulphur, eg by oxidation of the hydrogen sulphide employing ferric ions to produce sulphur and ferrous ions. Sulphur product issues from the stage 32 along flow line 34.
Product water leaves the stripping stage 22 along the flow line 42 and there is sufficient calcium hydroxide addition thereto along flow line 64 to reduce its pH to about 8. It is fed into the seder 44 for calcium carbonate crystals therein to settle.
Residual calcium carbonate crystals in the process water are settled in the stage 44 and issue from the stage 44 along flow line 48, as a by-product. Calcium carbonate produced in the towers 24 and issuing therefrom along flow lines 36 passes along flow line 38 into the calcium carbonate product flow line 48.
Calcium carbonate flow line 50, which feeds calcium carbonate into the flow line 12 as described above, branches from the flow line 48.
Finally, treated process water product issues .from precipitation stage 44 along flow line 46, from which it can be discharged into the environment. The flow line 52, which feeds water into the flow line 12 and which via flow line 60 feeds water into the anaerobic gas treatment stage 54, branches from the flow line 46.
Any selenates and/or tellurates in the raw water will be reduced biologically in 'the stage 18 from the respective Se(VI) and Te(VI) ions to the corresponding Se(IV) and Te(IV) ions, which in turn react with hydrogen sulphide in the stage 18 and precipitate as insoluble selenium and tellurium sulphides, which issue from the stage 18, together with sludge from stage 28, via flow line 21. If desired, a proportion of the sludge flowing rJ ~.~1 G :~
along flow line 21 can be recycled into the stage 18, to maintain a suitable solids content in the stage 18.
If the raw water being treated primarily contains selenate and tellurate ions, and not sulphate ions, then the process contemplates the possibility of adding some sulphate ions to the raw water in the flow line 12 upstream of the neutralization stage 14, eg as calcium sulphate, to enable selenate and tellurate ions to be removed from the water as described above.
Turning now to the embodiment of the present invention whereby nitrate ions are removed from the raw water which is treated, instead of sulphate ions, the main difference in the installatian is that the hydrogen sulphide stripping stage 22 is no longer required, and can be omitted in its entirety, including the stage 32, and the associated flow lines 28, 30 and 34, and the flow lines 36, 38 and 40.
In accordance with this embodiment of the process, the raw feed water contains dissolved nitrate and/or nitrite ions, and is typically more acidic than pH 5. Thus, tree fundamental difference between nitrate removal and sulphate/selenate/ tellurate removal is that in nitrate removal the anaerobic water treatment stage 18 does not act as a sulphate removal stage, but acts as a biological denitrification stage where nitrate and/or nitrite ions are biologically removed from the water by consumption thereof by suitable microorganisms, leading to the productian of nitrogen gas and carbonate and/or bicarbonate ions.
Once again the stage 18 is operated at a pH of 5 -8,5, preferably 6,5 - 7,5, sufficient calcium carbonate being added to the feed water via flow line 50, optionally with calcium hydroxide addition via flow line 62, to obtain such suitable pH.
In similar fashion, a metabolizable carbon source obtained from producer gas is added, as described above, .from the anaerobic gas treatment stage 54.
~ :y v ~.i e;~
The nitrogen prodvcad by the denitrification is not an 's environmental hazard, and can be discharged together with the product water into the environment, without any gas stripping ' stage.
5 In similar fashion, however, calcium hydroxide is added to the water along flow line 64 into the flow ll.ile 20/42 which leads directly from the stage 18 to the stage 44 so as to obtain a pH
of about 8 in the stage 44, for calcium carbonate precipitation.
Once again, calcium carbonate and water issue from stage 44 along 10 flow lines 48 and 46, together with the above described recirculation respectively of calcium carbonate and water along flow lines 50 and flow lines 52/60.
If desired, fatty acids (eg acetic acid, propionic acid and/or butyric acid) produced in the anaerobic gas treatment stage 54 15 and dissolved in water therein can be recovered as a by-product by withdrawing water from stage 54 via a flow line 66 (broken lines) and separating said fatty acids from this water, eg by concentration, evaporation or the like.
If the HzS concentration in the anaerobic water treatment stage 18 becomes excessively high, this may possibly adversely affect cultivation of microorganisms therein. The invention thus contemplates the possibility of recirculating water from flow line 42 to flow line 16 via a suitable flow line (not shown), to reduce H2S concentration in stage 18.
It is an advantage of the invention that it provides a versatile and flexible multi-purpose water treatment process, suitable for the removal of sulphate, selenate, tellurate, and/or nitrate ions from a raw water feed. Hydrogen sulphide [which can be converted to sulphur or other sulphur-containing materials] and calcium carbonate [which can be converted to lime and carbon dioxide] are produced as by-products.
Claims (11)
1. A process for the treatment of water containing dissolved anions which are members of the group consisting of sulphate ions, selenate ions, tellurate ions and nitrate ions, together with dissolved calcium cations, the process comprising the steps of:
passing the water at a pH of 5-8,5 through an anaerobic biological water treatment stage wherein microorganisms utilize said anions and reduce their concentration in the water; and passing the water from the anaerobic stage through a calcium carbonate, precipitation stage where calcium carbonate is precipitated from the water at a pH of at least 7,0, the process including the step of feeding producer gas through an anaerobic biological gas treatment stage wherein the proportion of hydrogen relative to carbon monoxide in the gas is increased, the gas from the anaerobic gas treatment stage then being fed into the anaerobic water treatment stage to provide a metabolizable energy source for the microorganisms in the anaerobic water treatment stage.
passing the water at a pH of 5-8,5 through an anaerobic biological water treatment stage wherein microorganisms utilize said anions and reduce their concentration in the water; and passing the water from the anaerobic stage through a calcium carbonate, precipitation stage where calcium carbonate is precipitated from the water at a pH of at least 7,0, the process including the step of feeding producer gas through an anaerobic biological gas treatment stage wherein the proportion of hydrogen relative to carbon monoxide in the gas is increased, the gas from the anaerobic gas treatment stage then being fed into the anaerobic water treatment stage to provide a metabolizable energy source for the microorganisms in the anaerobic water treatment stage.
2. A method as claimed in claim 1, in which the water being treated is acidic, the method including recirculating at least some of the calcium carbonate precipitated in the precipitation stage to the water being treated, upstream of the anaerobic water treatment stage, to increase the pH of the water before if enters the anaerobic water treatment stage, to said value of 5,0 - 8,5.
3. A process as claimed in claim 1, in which the water being trested contains sulphate ions, hydrogen sulphide being produced in the anaerobic water treatment stage, and the process comprising the step of passing water issuing from the anaerobic water treatment stage through a hydrogen sulphide removal stage before it passes on to the precipitation stage.
4. A process as claimed in claim 1, in which water being treated contains selenate ions and/or tellurate ions as the Se(VI) and Te(VI) ions respectively, the process including the step of adding sulphate ions to the water upstream of the anaerobic sulphate removal stage.
5. A process as claimed in claim 1, in which calcium carbonate is removed from the precipitation stage and is converted to lime and carbon dioxide by-products.
6. A process as claimed in claim 3, in which the hydrogen sulphide removed from the hydrogen sulphide removal stage is converted to sulphur as a by-product.
7. A process as claimed in claim 3, in which the microorganisms which utilize the sulphate ions comprise at least one species selected from the group consisting of:
Desulphovibrio desulphuricans Desulphovibrio vulgaris Desulphovibrio salexigens Desulphovibrio gigas Desulphovibrio africanus Desulphomaculum nigrificans Desulphomaculum ruminis Desulphomaculum orientis
Desulphovibrio desulphuricans Desulphovibrio vulgaris Desulphovibrio salexigens Desulphovibrio gigas Desulphovibrio africanus Desulphomaculum nigrificans Desulphomaculum ruminis Desulphomaculum orientis
8. A process as claimed in claim 3, in which water being treated is passed through a heavy metal recovery stage prior to any biological treatwent thereof, hydrogen sulphide from the hydrogen sulphide removal stage being fed to the heavy metal recovery stage to precipitate heavy metal as sulphide from the water.
9. A process as claimed in claim 1, in which the water being treated contains nitrate anions, said water being subjected to a denitrification in the anaerobic biological water treatment stage, the anaerobic biological water treatment stage containing microorganisms capable of utilizing nitrate ions, and comprising at least one species selected from the group consisting of:
Achromabacter spp. Enterobacter spp.
Aerobacter spp. Citrobacter spp.
Alcaligenes spp. Peptococcus spp.
Bacillus spp. Propionibacterium spp.
Flavobactarium spp.
Micrococcus spp.
Proteus spp.
Pseudomonas spp.
Achromabacter spp. Enterobacter spp.
Aerobacter spp. Citrobacter spp.
Alcaligenes spp. Peptococcus spp.
Bacillus spp. Propionibacterium spp.
Flavobactarium spp.
Micrococcus spp.
Proteus spp.
Pseudomonas spp.
10. A process as claimed in claim 1, in which microorganisms comprising at least one species selected from the group consisting of:
Rhodopseudomonas spp. Butyribacterium spp.
Sparomusa spp. Clostridium spp.
Acetobacterium spp. Desulphovibrio desulphuricans are utilized in the anaerobic gas treatment stage to increase the proportion of said hydrogen relative to said carbon monoxide.
Rhodopseudomonas spp. Butyribacterium spp.
Sparomusa spp. Clostridium spp.
Acetobacterium spp. Desulphovibrio desulphuricans are utilized in the anaerobic gas treatment stage to increase the proportion of said hydrogen relative to said carbon monoxide.
11. A process as claimed in claim 1, which includes the steps of withdrawing water from the anaerobic gas treatment stage and recovering one or more of fatty acids from this water as a by-product.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA897472 | 1989-10-02 | ||
| ZA89/7472 | 1989-10-02 |
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| Publication Number | Publication Date |
|---|---|
| CA2025433A1 CA2025433A1 (en) | 1991-04-03 |
| CA2025433C true CA2025433C (en) | 2001-02-20 |
Family
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2025433 Expired - Lifetime CA2025433C (en) | 1989-10-02 | 1990-09-19 | Treatment of water |
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| CA (1) | CA2025433C (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110482801B (en) * | 2019-09-19 | 2024-02-23 | 浙江艾摩柯斯环境科技有限公司 | Integrated biological synchronous denitrification and decalcification device for wastewater and method thereof |
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1990
- 1990-09-19 CA CA 2025433 patent/CA2025433C/en not_active Expired - Lifetime
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| CA2025433A1 (en) | 1991-04-03 |
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