GB2249785A - Process for removing nitrates from drinkable water by using membrane systems - Google Patents
Process for removing nitrates from drinkable water by using membrane systems Download PDFInfo
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- GB2249785A GB2249785A GB9124206A GB9124206A GB2249785A GB 2249785 A GB2249785 A GB 2249785A GB 9124206 A GB9124206 A GB 9124206A GB 9124206 A GB9124206 A GB 9124206A GB 2249785 A GB2249785 A GB 2249785A
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- water
- nitrates
- biomass
- denitrification
- drinking water
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 46
- 150000002823 nitrates Chemical class 0.000 title claims abstract description 43
- 238000000034 method Methods 0.000 title claims abstract description 39
- 230000008569 process Effects 0.000 title claims abstract description 39
- 239000012528 membrane Substances 0.000 title claims abstract description 27
- 239000003651 drinking water Substances 0.000 claims abstract description 31
- 235000020188 drinking water Nutrition 0.000 claims abstract description 31
- 238000000909 electrodialysis Methods 0.000 claims abstract description 27
- 238000011282 treatment Methods 0.000 claims abstract description 23
- 150000002500 ions Chemical class 0.000 claims abstract description 22
- 239000002351 wastewater Substances 0.000 claims abstract description 14
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 18
- 229910002651 NO3 Inorganic materials 0.000 claims description 16
- 239000002028 Biomass Substances 0.000 claims description 13
- 239000000463 material Substances 0.000 claims description 5
- 235000015097 nutrients Nutrition 0.000 claims description 5
- 230000031018 biological processes and functions Effects 0.000 claims description 4
- 238000002156 mixing Methods 0.000 claims description 4
- 238000005352 clarification Methods 0.000 claims description 2
- 229910010272 inorganic material Inorganic materials 0.000 claims 1
- 239000011147 inorganic material Substances 0.000 claims 1
- 230000003134 recirculating effect Effects 0.000 claims 1
- 230000000395 remineralizing effect Effects 0.000 claims 1
- 239000004576 sand Substances 0.000 claims 1
- 150000001805 chlorine compounds Chemical class 0.000 abstract description 9
- 150000003467 sulfuric acid derivatives Chemical class 0.000 abstract description 6
- 238000000746 purification Methods 0.000 abstract 1
- 150000003839 salts Chemical class 0.000 description 8
- 239000000126 substance Substances 0.000 description 8
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 6
- 230000008901 benefit Effects 0.000 description 6
- 238000005342 ion exchange Methods 0.000 description 6
- 230000001580 bacterial effect Effects 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 241000894006 Bacteria Species 0.000 description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 4
- 150000001450 anions Chemical class 0.000 description 4
- 239000003456 ion exchange resin Substances 0.000 description 4
- 229920003303 ion-exchange polymer Polymers 0.000 description 4
- 238000011084 recovery Methods 0.000 description 4
- 238000001223 reverse osmosis Methods 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 3
- 230000001651 autotrophic effect Effects 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 239000003795 chemical substances by application Substances 0.000 description 3
- 239000012141 concentrate Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000005265 energy consumption Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 239000012530 fluid Substances 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 230000008929 regeneration Effects 0.000 description 3
- 238000011069 regeneration method Methods 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 2
- 235000011941 Tilia x europaea Nutrition 0.000 description 2
- 125000000129 anionic group Chemical group 0.000 description 2
- 239000012267 brine Substances 0.000 description 2
- 125000002091 cationic group Chemical group 0.000 description 2
- 150000001768 cations Chemical class 0.000 description 2
- 238000011109 contamination Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000035622 drinking Effects 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 235000019441 ethanol Nutrition 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 230000008020 evaporation Effects 0.000 description 2
- 238000000265 homogenisation Methods 0.000 description 2
- 239000004571 lime Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 description 2
- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 1
- 235000011054 acetic acid Nutrition 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 230000002528 anti-freeze Effects 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 238000005115 demineralization Methods 0.000 description 1
- 230000002328 demineralizing effect Effects 0.000 description 1
- 230000007717 exclusion Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000007792 gaseous phase Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000008213 purified water Substances 0.000 description 1
- 238000004062 sedimentation Methods 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 235000015096 spirit Nutrition 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/469—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
- C02F1/4693—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis electrodialysis
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
- B01D61/44—Ion-selective electrodialysis
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/30—Aerobic and anaerobic processes
- C02F3/302—Nitrification and denitrification treatment
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/16—Nitrogen compounds, e.g. ammonia
- C02F2101/163—Nitrates
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2201/00—Apparatus for treatment of water, waste water or sewage
- C02F2201/46—Apparatus for electrochemical processes
- C02F2201/461—Electrolysis apparatus
- C02F2201/46105—Details relating to the electrolytic devices
- C02F2201/46115—Electrolytic cell with membranes or diaphragms
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Water Supply & Treatment (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Chemistry (AREA)
- Health & Medical Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Hydrology & Water Resources (AREA)
- Molecular Biology (AREA)
- General Chemical & Material Sciences (AREA)
- Electrochemistry (AREA)
- Analytical Chemistry (AREA)
- Urology & Nephrology (AREA)
- Biodiversity & Conservation Biology (AREA)
- Microbiology (AREA)
- Water Treatment By Electricity Or Magnetism (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
- Laminated Bodies (AREA)
- Wrappers (AREA)
Abstract
Process for removing nitrates and other ions, such as chlorides, sulphates and others, from drinking water, which consists in subjecting the crude water to be purified to a plurality of membrane purification means, particularly within electrodialysis units of the polarity-reversal type, arranged in series so as to allow the units to progressively purify the water until the concentration of nitrates and other ions is reduced at least below the limits prescribed by statutory provisions for drinking water, in then concentrating in a single flow "C" all the waste water in output from the electrodialysis units and in then subjecting the concentrated discharge flow "C" to a biological denitrification treatment, so as to obtain waste water with a content of nitrates and other ions which is within the limits set by the rules for waste water. <IMAGE>
Description
21 24 ?- 13 1 PROCESS FOR REMOVING NITRATES FROM DRINKABLE WATER BY USING
MEMBRANE SYSTEMS AND THE LIKE The present invention relates to a process for removing nitrates and other ionic components exceeding the statutory provisions from water intended for drinking, byusing membrane systems, particularly a polarity-reversal electrodialysis battery which uses membranes whichare alternately permeable to cations and to anions, in combination with a system for the denitrification of the discharge flow alone, capable of eliminating from the discharge brine the nitrates exceeding the statutory io provisions.
As is known, the content of nitrates in drinking water has progressively increased, forcing legislative bodies to intervene in order to set a maximum safety limit for human consumption. At the same time, the statutory provisions have set parameters for all the other ionic components of drinking water, making obsolete many conventional treatments which solve the problem partially (lime softening, ionexchange softening, selective nitrate removal on ion- exchange resins, biological aerobic or anaerobic denitrification) or fully, to the extent of requiring the remineralization of the product (reverse osmosis, evaporation systems).
The most recent statutory provisions, for example the EEC Directive No. 80/778 of July 15, 1980, the Decree pf the President of the Italian Cabinet dated February 8, 1985, have established, for nitrates, maximum acceptability limits for drinking water, which must not be exceeded, and guideline values to be observed for other chemical 1 2 parameters, including the hardness of the water, chlorides, sulphates, sodium and total dissolved solids (TDS), as well as acceptability limits for nitrates present in discharge water; said limits, according to the most recent provisions, are specified as 20 ppm as nitrogen or as 88.5 ppm as N03.
The technology used so far tends to cope with one problem at a time in order to improve the drinkability characteristics of the water, i.e.:
- lime softening or ion-exchange resin softening to 10 reduce hardness; selective ion-exchange resins treatments for nitrate removal; or biological - electrodialysis or reverse osmosis for reducing the total dissolved salts (TDS), chlorides and sulphates, particularly in the treatment of salt water.
The new statutory provisions instead require the treatment of the problem of drinking water in a global sense, since very often the available water is not drinkable due to several parameters and not only due to its nitrate 20 content or to its chloride content.
Among the various known processes, only the one which uses electrodialysis units, and especially units for polarity-reversal electrodialysis (EDR), allows removal of nitrates from water while simultaneously reducing other polluting agents within the maximum acceptability threshold of the new provisions, furthermore allowing to approximate or reach the indicated guideline values in an economical and energy-wise optimum manner.
Furthermore, since this process is constituted by 30 successive stages, it allows stopping the treatment at the 1 1 1 j 3 actual requirements of the available water source.
It should in any case be noted that the known systems, such as reverse osmosis and evaporation, by producing an excessive demineralization, require remineralization, either with chemical products or by mixing with crude water, in order to provide drinkability.
It should also be noted, as will become apparent hereinafter, that the use of EDR units allows quantitatively equivalent removals both for chloride and for nitrates, 10 allowing the nitrates to drop below the maximum allowed threshold and the chlorides to approximate or improve the guideline value of the statutory provisions.
All the known nitrate removal processes, including electrodialysis and with the only exception of those which perform the biological nitrate removal treatment directly on the drinking water, have the disadvantage of collecting the removed nitrates in the discharge flows, so that the content of said flows can exceed the acceptable values established by the statutory provisions for waste water. A further 20 treatment is therefore necessary in order to include the discharge flow, too, within the limits set by the law.
Biological treatment performed directly on the drinking water instead leads to another severe disadvantage, which is due to the fact that the direct contact and permanence of bacteria in the drinking water, which is technically possible, can cause damage to the human body. It is in particular this possibility of the presence of bacteria which the present invention has the purpose of eliminating completely.
The aim of the present invention is therefore to 4 provide a process for removing nitrates (and other harmful ions) from drinking water, which allows, by means of a particular combined process of water treatment by means of membrane systems and of denitrification of the waste water separately from the drinking water, achievement of the values prescribed by the statutory provisions both for the drinking water and for the waste water.
An object of the invention is to provide a nitrate removal process which is conceived so as to allow stopping the nitrate removal treatment at the values set by the statutory provisions for drinking water, so as to allow the simultaneous removal, together with the nitrates, also of the chlorides, sulphates, of the hardness and total dissolved solids, as well as to ensure the constant quality of the produced water when the chemical characteristics of the crude fed water are correspondingly constant.
A further object of the invention is to provide a process of the above specified type which can provide a high yield in drinking water and also does not require any 20 particular mixing, homogenations and remineralizations of the water produced, with evident economical and practical advantages, and is also highly advantageous, with respect to the nitrate removal processes currently in use, in terms of area occupation, of facility cost and operating cost.
This aim, these objects and others which will become apparent from the following description are achieved by a process for removing nitrates from drinking water, which consists, according to the present invention, in subjecting the crude feed water to a treatment for the removal of 30 nitrates and other ions present in said water within a plurality of membrane purifying elements, particularly a plurality of units for electrodialysis of the polarity- reversal type, arranged in series so as to allow each membrane unit to progressively purify the water, until a removal of chlorides, degree of provisions the nitrates and of other ions, such as sulphates and the like, such as to ensure the drinkability prescribed by the statutory for drinking water is obtained; in then subjecting said nitrates and other ions, removed by said 10 units, to a biological denitrification treatment by means of known technologies, so as to comply with the limit nitrate content set by the applicable statutory provisions for the waste water as well.
Further characteristics and advantages of the process according to the invention will become apparent from the following detailed description of a preferred but not exclusive practical embodiment thereof, which is given with reference to the accompanying drawings, provided only by way of non-limitative example and wherein:
figure 1 is a block diagram of the individually known apparatuses which can be used to carry out the operating steps of the nitrate removal process according to the invention, and figure 2 is a schematic view of a series of electrodialysis units with reverse-polarity membranes, used to separate, according to the invention, the nitrates and other ions from the drinking water and to removethe nitrate-enriched discharge flows emitted by said electrodialysis units, for a successive and separate overall denitrification treatment.
i 6 With reference to figure 1, the crude water to be treated, appropriately filtered in order to remove any foreign solid matter, is conveyed, by means of a pipe A, into a plurality of units or cells for electrodialysis with reverse-polarity membranes which are arranged mutually in series and in a number suitable for obtaining the removal of the nitrates, chlorides and the like, until their concentration in the water is reduced below the limits of the statutory provisions for drinking water. The water 10 purified by the various units, as will become apparent hereinafter, is conveyed by means of a pipe B to the user facilities, whereas the discharge flows from the units are combined and, by means of a pipe C, are conveyed to a biological denitrification unit D where, after treatment with the addition of organic nutrient substances E fed by means of a pipe F, the nitrate-free discharge flow is conveyed to landfills by means of a pipe G.
More particularly, the operating steps for the removal of the nitrates by-means of a membrane system constituted by 20 electrodialysis units with reverse-polarity membranes can be summarized as follows.
With reference to said figure 2, an electrodialysis system is substantially constituted by a parallelepipedal container H inside which a plurality of equally spaced vertical membranes is arranged; said membranes define compartments or cells indicated by the numerals 1 to 6,.
The membranes are of the anionic type and of the cationic type and are arranged alternatively inside the container 4; the end compartments 1 and 6 contain the 30 electrodes, and specifically the cathode in the compartment 4 i i 7 1 and the anode in the compartment 6. Said electrodes are connected to a direct-current electric power source 7. By means of this arrangement, the electrodialysis system is capable of maintaining a constant quality of the purified water by reversing the polarities of the electric current fed by the source 7. The crude water is in fact fed continuously into the compartments comprised between the first one and the last one of the series, and the membranes separate the dissolved ionized impurities (nitrates, chlorides, etc.).
More precisely, in figure 2 the membranes are indicated in pairs, i.e. with the letters I and L for each contiguous pair.
The membranes indicated by "I" are of the anionic type, are impermeable to water and allow the passage of negatively charged ions (anions).
The membranes indicated by IILII are of the cationic type, are impermeable to water and allow the passage of positively charged ions (cations). As regards the cells or compartments, the compartments 1 and 6 are special compartments, since they contain the electrodes, whereas the others respectively perform the following functions:
- compartment 2 - N03 and other negatively charged ions cannot pass through the membrane IILII and remain in compartment 2.
- compartment 3 - Na+ and other positively charge4 ions cannot pass through the membrane "I" and remain in compartment 3.
- compartment 4 - N03 and other negatively charged ions pass through the membrane "I" into compartment 5. Na+ and 8 other positively charged ions pass through the membrane I'Ll' into compartment 3.
- compartment 5 N03 and other negatively charged ions cannot pass through the membrane I'Ll' and remain in compartment 5.
Na+ and other positively charged ions cannot pass through the membrane "I" and remain in the compartment 5.
The overall result is that the water of compartments 2 and 4 has been depleted of the nitrates and other ions and 10 as such can be collected and distributed for drinking. The water of compartments 3 and 5 has enriched in nitrates and other ions and constitutes the discharge flow.
The overall treatment, exemplified in the diagram of figure 2, collects the discharge flows and combines them in a single discharge flow "C" which can thus be subjected to a biological denitrification treatment in a reactor (or in a fluid bed) D (figure 1) separately from the drinking water.
The removal of the nitrates from the discharge flow of the electrodialysis unit is performed biologically according to the present invention by means of bacterial populations.
Conceptually, it is possible to use both heterotrophic and autotrophic strains.
The greater complexity of the use of autotrophic bacteria (including the need to use hydrogen as a nutrient) limits their advantages to some hypotheses of very particular installations which are not considered herein.
Heterotrophic bacteria instead require an addition of organic substances. Among these, mention can be made of the following: methyl alcohol, acetic acid and ethyl alcohol, as 30 well as numerous by-products of industry, such as for 1 1 9 example:
- tailings from the production of alcohol and distilled spirits, - waste sugary concentrates, - antifreeze mixtures of cooling circuits.
Due to the low acquisition cost of these substances, the advantage of the proposed process is evident.
The consumption of organic substances is in fact proportional to the mass of nitrates which must be removed lo from the water to be purified, and is instead not proportional to the entire nitrate content of said water, as occurs for example for processes based on the direct biological denitrification of the water to be purified.
The biochemical denitrification reaction is extensively described by the literature in its biological, equilibrium, kinetic and technological aspects. Said biological process can be performed by adopting one of the following three technologies, which are already known and described by the literature: 20 - submerged adhered biomass in a fixed or fluidized bed, non-submerged adhered biomass, - suspended biomass.
In the first hypothesis, the waste water of the electrodialysis, to which methyl alcohol or another suitable source of carbon is conveniently added, flows through a bed of inert material to which the bacterial colonieswhich perform denitrification adhere. The inert material can be fixed or fluidized by the flow speed.
The second process differs from the preceding one since 1 the flow to be subjected to denitrification does not entirely occupy the empty spaces between the inert material. The residual empty space is thus occupied by a gaseous phase which must not contain oxygen.
In the third process, the biologicaldenitrification mass is kept suspended in the liquid phase in a reactor to which both the fluid to be subjected to denitrification and the carbon source are fed.
The mixture of biomass/denitrified fluid which leaves the reactor is separated in a gravity sedimentation unit and the biomass is continuously returned to the reactor.
In industrial application, the above-mentioned processes differ markedly from one another in terms of area occupation, facility cost and operating costs.
The choice must therefore be performed on a case-by- case basis, taking into account both the operating conditions (flow-rate to be subjected to denitrification, load of nitrates to be removed, temperature) and the external conditions (availability of space, environmental 20 impact, technological level of the area, availability of the nutrient, etc.).
For a greater clarification and for a confirmation of the above, two examples of practical execution of the combined process of electrodialysis and subsequent separate denitrification of the discharge flow, executed according to the invention, are reported hereinafter.
Example 1
The following results were obtained for a three-month period in a pilot plant using electrodialysis units 1 11 manufactured by the IONICS Inc. company, of the Aquamite XX 4/2 type, capable of producing 50 m 3 /h of drinking water, with 4 m 3 /h of discharge flow, i.e. with a 92% recovery.
TDS Feed Output Removal Output Removal Discharge 1st % 2nd % flow stage stage PPM ppin PPM Na 12.6 11.8 6.4 10.4 17.5 38 Ca 92 66 28 44 52 790 cl 30 20 34 12 60 250 S04 67 97 45 19 72 760 N03 52 37.9 27 23 56 474 TDS 422 312 26 215 49 3238 Since the acceptability limit for nitrates in discharge 15 water is 20 ppm as nitrogen or 88.5 ppm as N03. it is necessary to subject the discharge flow to denitrification. Said denitrification was achieved with a biological system which easily obtains a reduction which is far greater than the 88.5% prescribed by the statutory provisions.
Example 2
The following results were obtained, after approximately three months, in a second pilot plant which also used an Aquamite XX 4/2 electrodialysis unit, preset for producing 50 m 3 /h of drinking water with a concentrated 25 discharge flow of 8.8 m 3 1h and therefore with an 85% recovery.
12 Feed PPM output Removal Dipcharge 2nd flow stage PPM PPM Na 35 22 20 113 Ca 140 70 so 467 HC03 450 292.5 35 1052 cl 54 23.8 56 202 S04 so 24 70 374 N03 71.7 32 55 265 TDS 870.7 484 45 2606 In this case also, the N03 concentration in the discharge flow exceeds by 177 ppm (265-88) the concentration limit (88.5) prescribed by the statutory provisions.
Since electrodialysis requires in practice only the use of electric power and since the consumption of said electric power is proportional to the amount of salts removed, it is evident that the staged system is the one which entails the lowest energy consumption.
In the electrodialysis system, the water fed to the system is always more than the water produced:
the ratio between the produced water (Qp) and the fed water (Qa) is termed Recovery (R) of the system 1 QP R= ----- Qa QP QP+S z 1 i where S is the concentrated discharge of the system. It is evident that the energy consumption is smaller as S decreases, i.e. electrodialysis and for electrodialysis with as R approaches 1.
Systems for polarity reversal are, among the known ones, those which allow maximum recovery.
Bearing in mind that the removed nitrates are concentrated in the discharge flow and that therefore content thereof can be higher than the values accepted 10 the applicable statutory provisions for waste water, all the by the need arises for a further treatment in order to make the discharge flow also comply with the statutory limits. It is noted that this need is also shared by other treatment systems, such as reverse osmosis and selective ion exchange.
Two important aspects must furthermore be taken into account:
- the denitrification kinetics decreases rapidly as the temperature decreases. Since in the electrodialysis process the temperature at which the discharge flow is released is 20 higher than the temperature of the water to be purified, the process according to the present invention allows operation in more favorable kinetic conditions with respect to the process of direct denitrification of the crude water; - the biological denitrification process is hindered by a high salinity of the stream to be subjected to denitrification. The advantage of the process according to the invention with respect to ion-exchange systems, in which the salinity of the stream to be subjected to denitrification is increased considerably by the sodium 30 chloride used to regenerate the ion exchanger, is therefore 14 obvious.
The denitrification system applied to the concentrated flow obtained from the polarity-reversal electrodialysis unit can be applied to any other membrane system which concentrates the nitrates in a single discharge flow.
After the above description, in order to better point out the differences of the present process with respect to the latest and most efficient nitrate removal processes applied on an industrial scale, the following is noted:
a) Selective ion-exchange process Treatments with varying degrees of sophistication have been adopted by using selective ion-exchange resins, i.e.
resins which have a particularly high affinity for nitrates. The nitrates are always exchanged by replacement with other anions, and the nitrate reduction is always equivalent to the increase in other anions. The systems are cyclic and cannot ensure a constant quality of the product without having storage volumes for homogenizing the drinking water produced in the cycle.
The discharge brine arriving from the regeneration of the resins introduces other salts which, by altering the overall mass balance, produce a negative environmental impact and do not cope with the problems of nitrates in the waste water and of the increase in salts in the waste water.
A particularly original system entails the biological denitrification of the regeneration eluate, while reducing but not eliminating the external addition of salts.
However, the denitrified concentrate is placed in contact with the ion-exchange column intended for the subsequent service, and therefore the potential risk of h, i 1 i is bacterial contamination of the drinking water remains.
b) Biological processes Various biological systems, both autotrophic and heterotrophic, by now extensively known in the literature, have been used.
- All the above-mentioned systems entail the direct action of the bacterial activity on the drinking water, and all the systems force the total removal of the nitrates with an addition of organic carbon in excess of the actual requirements.
Finally, the economic, practical and energy advantages obtained with the process according to the invention can be simmarized as follows.
- Possibility of stopping the nitrate removal treatment at the actual requirements determined by the statutory provisions or by the requirements of the local Health Authorities.
- Simultaneous removal of nitrates, chlorides, sulphates, hardness and TDS, with the possibility of obtaining, with a single treatment, the adaptation of the chemical characteristics of the drinking water to the statutory provisions or in general of improving the characteristics of said water.
- Constant quality of the produced water, with variations related exclusively to the variations in the composition of the feed source.
- No need for remineralizations, mixings, storage for homogenation.
- The purifying system is absolutely independent of the biological denitrification system, with the absolute f 16 exclusion of the possibility of a bacterial contamination of the drinking water induced by the biological process.
- Energy consumption exactly equivalent to the amount of salts or nitrates removed.
- The overall mass balance remains absolutely unchanged, since no addition of reactive agents or regeneration agents, intended to increase the overall saline content of the fed water, is provided.
The nitrates are removed from the feed water without being replaced with other salts as in the typical case of ion exchange, which replaces the nitrate ion with the chloride ion.
R i 17
Claims (6)
1 1. Process for removing nitrates from drinking water, 2 characterized in that it consists in subjecting the crude 3 water to be purified to a plurality of membranepurifying 4 elements, particularly within electrodialysis units preferably of the polarity-reversal type, arranged in series 6 so as to allow each of said units to progressively purify 7 the water until the concentration of nitrates and other ions 8 is reduced at least within the limits prescribed by the statutory provisions for drinking water, in then concentrating in a single flow all the waste water flowing out of said electrodialysis units and in then subjecting 12 said concentrated discharge flow to a biological 13 denitrification treatment, so as to obtain waste water with 14 a content of nitrates and other ions which is within the limits set by the rules for waste water.
1
2. Process according to claim 1, characterized in that 2 said drinking water is obtained with the drinkability 3 characteristics required by the statutory provisions in a 4 direct and continuous manner and with constant quality, without requiring operations for mixing, homogenizing and 6 remineralizing the produced water.
1
3. Process according to claim 1, characterized in that 2 said biological denitrification is applied only to the 3 concentrated flow of a nitrate removal membrane systein, in 4 order to prevent even the merely potential contact between 5 the biological denitrification process and the process for 6 removing the nitrates from the drinking water.
1
4. Process according to claims 1 and 3, characterized 18 2in that said process for the denitrification of the 3 concentrated discharge flow is obtained by means of a 4 conventional biological process which is constituted by an oxygen-free reactor with suspended biomass, by a 6 clarification unit for separating the biomasses from the 7 denitrified flow, by devices for recirculating the biomass 8 to the reactor, and by devices for the dosage of the organic 9 nutrient.
1
5. Process according to claims 1 and 4, characterized 2 in that said process for the denitrification of the 3 concentrated discharge flow is constituted by oxygen-free 4 adhered- biomass reactors chosen among:
- adhered biomass introduced on a fixed support, 6 wherein said support is constituted by inorganic material or 7 by structures made of plastic material, 8 - fluidized adhered biomass, the support of the biomass 9 being constituted by sand or other material suitable for providing a fluidized bed.
11 - adhered biomass on a non-immersed fixed support, 12 which comprises devices for separating the excess biomass 13 from the denitrified flow, devices for the dosage of the 14 organic nutrient, and auxiliary devices.
1
6. Process for removing nitrates and other ions from 2 drinking water substantially as described with reference to 3 the accompanying drawings.
I!
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
IT02207990A IT1245742B (en) | 1990-11-16 | 1990-11-16 | PROCEDURE FOR THE REMOVAL OF NITRATES FROM WATERS FOR DRINKING USE BY USING MEMBRANE AND SIMILAR SYSTEMS. |
Publications (3)
Publication Number | Publication Date |
---|---|
GB9124206D0 GB9124206D0 (en) | 1992-01-08 |
GB2249785A true GB2249785A (en) | 1992-05-20 |
GB2249785B GB2249785B (en) | 1994-08-24 |
Family
ID=11191171
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB9124206A Expired - Fee Related GB2249785B (en) | 1990-11-16 | 1991-11-14 | Process for removing nitrates from drinkable water by using membrane systems and the like |
Country Status (5)
Country | Link |
---|---|
DE (1) | DE4137725A1 (en) |
FR (1) | FR2669324B1 (en) |
GB (1) | GB2249785B (en) |
IL (1) | IL99932A (en) |
IT (1) | IT1245742B (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2001040118A1 (en) * | 1999-12-06 | 2001-06-07 | Instituto De Biologia Experimental E Tecnológica (Ibet) | Treatment of aqueous media containing electrically charged compounds |
WO2006135188A1 (en) * | 2005-06-14 | 2006-12-21 | Korea Power Engineering Company, Inc. | Electrodialysis reversal and electrochemical wastewater treatment method of compound containing nitrogen |
NL2003812C2 (en) * | 2009-11-17 | 2011-05-18 | Stichting Wetsus Ct Excellence Sustainable Water Technology | Bio-electrochemical device and method for upgrading a fluid. |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6373010B1 (en) | 2000-03-17 | 2002-04-16 | General Electric Company | Adjustable energy storage mechanism for a circuit breaker motor operator |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE3505651A1 (en) * | 1985-02-19 | 1986-08-21 | Metallgesellschaft Ag, 6000 Frankfurt | Process for removing nitrate from ground water |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CH677325A5 (en) * | 1989-04-28 | 1991-05-15 | Asea Brown Boveri |
-
1990
- 1990-11-16 IT IT02207990A patent/IT1245742B/en active IP Right Grant
-
1991
- 1991-11-01 IL IL9993291A patent/IL99932A/en not_active IP Right Cessation
- 1991-11-13 FR FR9113933A patent/FR2669324B1/en not_active Expired - Fee Related
- 1991-11-14 GB GB9124206A patent/GB2249785B/en not_active Expired - Fee Related
- 1991-11-15 DE DE4137725A patent/DE4137725A1/en not_active Withdrawn
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE3505651A1 (en) * | 1985-02-19 | 1986-08-21 | Metallgesellschaft Ag, 6000 Frankfurt | Process for removing nitrate from ground water |
Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2001040118A1 (en) * | 1999-12-06 | 2001-06-07 | Instituto De Biologia Experimental E Tecnológica (Ibet) | Treatment of aqueous media containing electrically charged compounds |
US6960299B2 (en) | 1999-12-06 | 2005-11-01 | Intstituto De Biologia Experimental E Technologia | Treatment of aqueous media containing electrically charged compounds |
WO2006135188A1 (en) * | 2005-06-14 | 2006-12-21 | Korea Power Engineering Company, Inc. | Electrodialysis reversal and electrochemical wastewater treatment method of compound containing nitrogen |
KR100687095B1 (en) | 2005-06-14 | 2007-02-26 | 한국전력기술 주식회사 | Electrodialysis reversal and electrochemical wastewater treatment process of compound containing nitrogen |
CN101198550B (en) * | 2005-06-14 | 2012-06-13 | 韩国电力技术株式会社 | Electrodialysis reversal and electrochemical wastewater treatment method of compound containing nitrogen |
NL2003812C2 (en) * | 2009-11-17 | 2011-05-18 | Stichting Wetsus Ct Excellence Sustainable Water Technology | Bio-electrochemical device and method for upgrading a fluid. |
WO2011062485A2 (en) | 2009-11-17 | 2011-05-26 | Stichting Wetsus Centre Of Excellence For Sustainable Water Technology | Bio-electrochemical device and method for upgrading a fluid |
WO2011062485A3 (en) * | 2009-11-17 | 2011-07-07 | Stichting Wetsus Centre Of Excellence For Sustainable Water Technology | Bio-electrochemical device and method for upgrading a fluid |
Also Published As
Publication number | Publication date |
---|---|
DE4137725A1 (en) | 1992-05-21 |
IT1245742B (en) | 1994-10-14 |
IL99932A (en) | 1995-03-30 |
FR2669324A1 (en) | 1992-05-22 |
GB2249785B (en) | 1994-08-24 |
IT9022079A0 (en) | 1990-11-16 |
IT9022079A1 (en) | 1992-05-17 |
FR2669324B1 (en) | 1994-10-28 |
GB9124206D0 (en) | 1992-01-08 |
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PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20061114 |