Claims:1. An integrated process for reducing Total Dissolved Salt (TDS) content of water by atleast 80%, wherein said process comprises steps of:
subjecting the water provided as feed to microfiltration to obtain filtered water; followed by subjecting the filtered water to nanofiltration through anionic nanofiltration membrane to obtain a permeate stream and a reject stream, wherein the TDS content of the permeate stream is reduced by at least 80% when compared to the feed; and
optionally subjecting the reject stream to chemical precipitation, wherein chloride content of water from the reject stream is reduced by at least 80%.

2. The process as claimed in claim 1, wherein the microfiltration is a multi-step process for removing oily material, turbidity and suspended solids comprising atleast a first and a second filtration step, and wherein the filtration is selected from a group comprising:
pressure sand filtration; and
micro cartridge filtration,
or a combination thereof.

3. The process as claimed in claim 2, wherein the microfiltration is a cross-flow filtration; wherein permeate from the first filtration step is subjected to the second filtration step; and wherein said permeate is subjected to anti-scalant dosing and acid dosing before being subjected to the second filtration step.

4. The process as claimed in claim 2, wherein size of sand particles in the pressure sand filter is about 12 micron; and wherein the micro cartridge filter has porosity of about 150 microns, and length ranging from about 5 to 40 inches.

5. The process as claimed in claim 1, wherein the nanofiltration is a multi-step process comprising atleast 2 nanofiltration steps; wherein the anionic nanofiltration membrane has pore size of about 0.4nm; and wherein the anionic nanofiltration membrane at each nanofiltration step is same.

6. The process as claimed in claim 5, wherein the nanofiltration is a cross-flow membrane filtration; wherein permeate flux around the nanofiltration membrane ranges from about 25 L/hr/m2 to 30 L/hr/m2 and wherein the anionic nanofiltration membrane rejects monovalent and divalent salts present in the filtered water received from the microfiltration step by Donnan exclusion principle to obtain permeate with reduced TDS.

7. The process as claimed in claim 6, wherein the membrane repels chloride ions and allows water to pass; and wherein each step of nanofiltration reduces chloride ions by at least 30%.

8. The process as claimed in claim 1, wherein permeate from the nanofiltration step is subjected to pH correction prior to being recycled for industrial application.

9. The process as claimed in claim 1, wherein the chemical precipitation is a two-step process comprising:
a first settling step; and
a second settling step.

10. The process as claimed in claim 9, wherein reject stream from the nanofiltration step is subjected to the first settling step by addition of lime and sodium aluminate, along with a flocculant; followed by agitating the stream; and allowing settling of slurry from the reject stream.

11. The process as claimed in claim 10, wherein permeate from the first settling step is subjected to the second settling step to allow further settling of slurry.

12. The process as claimed in claim 9, wherein both the first and the second settling steps comprise addition of acetic acid for pH adjustment; and wherein slurry from both the first and the second settling steps is solid sludge; wherein the solid sludge has moisture content of less than 5% and alumina content of about 7% to 9%.

13. The process as claimed in claim 11, wherein permeate from the second settling step is further passed through additional filter(s) selected from a group comprising pressure filter, cartridge filter or any combination thereof; and wherein permeate from said filter(s) has suspended solid level ranging from about 30NTU to 50NTU.

14. The process as claimed in claim 9, wherein the chemical precipitation results in precipitation of monovalent and divalent salts as calcium aluminium salts selected from calcium chloro aluminate or calcium sulpho aluminate or a combination thereof.

15. The process as claimed in claim 1, wherein the permeate from the nano-filtration step has chloride content reduced by about 70% to 75%; silica content reduced by about 70% to 99%; sodium content reduced by about 65% to 70%; and sulphate ion content reduced by about 80% to 97%, when compared to the feed.

16. The process as claimed in claim 1, wherein said chemical precipitation reduces silica in the reject stream by atleast 80%; and sulphate ion in the reject stream by atleast 80%.

17. The process as claimed in claim 1, wherein the water with reduced TDS content is used in quenching of coke.

18. Use of solid sludge as claimed in claim 12 as a coating material.

19. A process for reducing chloride content of water by at least 80%, wherein said process comprises steps of:
subjecting the water to chemical precipitation by a first settling step of adding lime and sodium aluminate, along with a flocculant; followed by a second settling step for settling of slurry.

20. A system for reducing Total Dissolved Salt (TDS) content of water, said system comprising:
a feed tank (1) connected to a water inlet (0);
a microfiltration unit connected to the feed tank wherein the microfiltration unit is configured with a first filter (3) and a second filter (4) for filtering the water;
a nano-filtration membrane assembly (9) comprising
atleast two anionic nanofiltration membranes connected to the microfiltration unit wherein the nano-filtration membrane assembly receives filtered water from the microfiltration unit;
wherein permeate stream from the nano-filtration membrane assembly has TDS content reduced by atleast 80%;
optionally, a chemical precipitation unit (12) connected to the nano-filtration membrane assembly to receive reject stream from the nano-filtration membrane assembly, configured with
a first settling tank (V01), and
a second settling tank (V03), to obtain water with chloride content reduced by atleast 80%.

21. The system as claimed in claim 20, wherein the feed tank (1) is connected to the microfiltration unit (3) through a feed pump (2) that pumps feed from outlet of the feed tank to the microfiltration unit.

22. The system as claimed in claim 20, wherein the first filter (3) and the second filter (4) are selected from a group comprising:
pressure sand filter; and
micro cartridge filter,
or a combination thereof.

23. The system as claimed in claim 20, wherein in the microfiltration unit, permeate from the first filter (3) is fed to the second filter (4) for further filtration; wherein feed stream to the second filter is connected to an antiscalant dosing device (5) and an acid dosing device (6) which add antiscalant and acid to said feed stream to maintain neutral pH of the feed stream and prevent scale formation on filter membrane.

24. The system as claimed in claim 20, wherein the microfiltration unit is connected to the nanofiltration membrane assembly (9) through a high-pressure pump (7).

25. The system as claimed in claim 20, wherein permeate stream from the nano-filtration membrane assembly (9) is connected to a pH correction unit (10) for correcting pH of the permeate and wherein said permeate has TDS reduced by atleast 80% and is transferred to storage tank (11); and wherein reject from the nano-filtration membrane assembly is sent as feed to the chemical precipitation unit (12).

26. The system as claimed in claim 20, wherein the chemical precipitation (12) unit further comprises a lime slacker tank (T02), a sodium aluminate tank (T04); an acetic acid tank (T03) and a flocculant dosing pump, wherein the lime slacker tank (T02), sodium aluminate tank (T04) and acetic acid tank (T03) comprise inlet for fresh water.

27. The system as claimed in claim 26, wherein the first settling tank (V01) of the chemical precipitation unit comprises an inlet for water supply, the feed, the lime, the sodium aluminate, the acetic acid and the flocculant; wherein the first settling tank further comprises a stirrer to subject mixture of the feed and the lime, the sodium aluminate, the acetic acid and the flocculant to agitation, before allowing settling of slurry.

28. The system as claimed in claim 27, wherein the first settling tank (V01) is connected to a pit and to the second settling tank (V02); wherein the slurry from the first settling tank is sent to the pit (UC) and permeate from said first settling tank is sent to the second settling tank (V02); wherein said connections to the pit and to the second settling tank are through a pressure filter (PF01).

29. The system as claimed in claim 28, wherein the second settling tank (V02) has inlet for permeate from the first settling tank (V01) and inlet for the acetic acid; wherein the second settling tank is connected to a pit (UC) and a pressure sand filter (F01); wherein after allowing settling to occur, slurry is sent to the pit and permeate is sent as feed to the pressure sand filter.

30. The system as claimed in claim 29, wherein the pressure sand filter (F01) is connected to a pit (UC) and a microcartridge filter (T05); wherein slurry from the pressure sand filter is sent to the pit and permeate from the pressure sand filter is sent as feed to the microcartridge filter.

31. The system as claimed in claim 30, wherein permeate from the microcartridge filter (T05) is connected to a storage tank and has chloride content reduced by atleast 80% when compared to reject from the nano-filtration membrane assembly.
, Description:TECHNICAL FIELD
The present disclosure relates to the field of water treatment. Particularly, the disclosure relates to an integrated process for reducing Total Dissolved Salts content in water. Said process comprises a microfiltration step, a nano-filtration and optionally, a chemical precipitation step. Further embodiments of the present disclosure disclose a system for reducing the Total Dissolved Salts content in water introduced to the system.

BACKGROUND OF THE DISCLOSURE
Contamination of surface water with different ions is a major environmental concern throughout the world. As an example, use of seawater in different stages of industrial processes increases concentration of contaminants such as chloride in water bodies by directing their waste streams into said water bodies. Industries, especially, agricultural, petroleum, leather and steel require sea water for cooling, quenching, scrubbing, etc. As a result, wastewater from these industries becomes highly saline and rich in organic and inorganic materials.
In view of the fact that only 3% of surface water is potable, increasing concentration of ions caused by industrial discharge, has posed a serious threat to utilization of water from natural sources. Among various ions, chloride has been reported to be the most dangerous owing to its small size, high electronegativity and super-reactivity. Eventually, it gets mixed up with surface water (pond, river, sea, etc.) through the water cycle and contaminates drinking water. Intake of chloride-rich water leads to damage of gill tissues of aquatic animals. Over exposure of chloride threatens human health, posing risk of cancer.
Apart from health risks posed by high chloride content in water making it unfit for human consumption, chloride contamination of water affects use of water in industries such as fuel industries that use said water in the coke quenching process.
Chloride is a deleterious ionic species in coke quenching water because it promotes corrosion in blast furnace due to raw material (coke) quenched by high-chloride content water being fed into the blast furnace. Usage of sea-water for coke quenching can be identified as the origin for the high chloride content due to which this water becomes corrosive for pipelines.
Further, high chloride content in water bodies also poses serious threat to aquatic life. Thus, there is a requirement of efficient, less energy intensive and highly scalable technology to improve overall quality of the discharged effluent.
Ion exchange, biosorption, freezing, solar and geothermal desalination, distillation, are some of the commercially used technologies for purification of water. However, low throughput and poor removal efficiency make these difficult for application in industrial scale. Ion exchange process removes the chloride in an efficient manner and provides high throughput but involves high maintenance cost due to the regeneration cost of resin and fouling due to salt deposition, organic, bacterial and chlorine contamination from resin. Biosorption, solar and geothermal desalination, though environment friendly processes, have low throughput. Further requirement of high treatment time and high surface area makes said processes non-feasible for industrial application. Furthermore, none of these existing processes provide for re-use/recycle or further treatment of membrane reject material.
The available technologies for membrane reject treatment are multi-effect evaporation or natural evaporation. However high operation and maintenance cost associated with said technologies render them unfit for industrial application.
Further, membrane based separation processes offer alternative energy-efficient route. Reverse osmosis (RO), for example, is a very popular technique for deionization and dechlorination of water. However, requirement of high transmembrane pressure (TMP) (around 25 atm) and low throughput, restricts its large scale real life application. Size exclusion, is another existing technique, which however struggles to achieve removal of small sized ions.
Therefore, in view of the draw-backs associated with existing technologies, a high-throughput, energy efficient and economical method that provides ease of scale up and minimum generation of pollutants is the need of the hour.
STATEMENT OF THE DISCLOSURE
Accordingly, the present disclosure provides an integrated process for reducing Total Dissolved Salt (TDS) content of water by atleast 80%, wherein said process comprises steps of:
subjecting the water provided as feed to microfiltration to obtain filtered water; followed by subjecting the filtered water to nanofiltration through anionic nanofiltration membrane to obtain a permeate stream and a reject stream, wherein the TDS content of the permeate stream is reduced by at least 80% when compared to the feed; and
optionally subjecting the reject stream from the nanofiltration step to chemical precipitation, , wherein chloride content of water from the reject stream is reduced by at least 80%.
The permeate from the nano-filtration step has chloride content reduced by about 70% to 75%; silica content reduced by about 70% to 99%; sodium content reduced by about 65% to 70%; and sulphate ion content reduced by about 80% to 97%, when compared to the feed.
The chemical precipitation step reduces silica in the reject stream from the nanofiltration step by atleast 80%; and sulphate ion in the reject stream by atleast 80%.

Further, the present disclosure provides a system for reducing Total Dissolved Salt (TDS) content of water, said system comprising:

a feed tank (1) connected to a water inlet (0);
a microfiltration unit connected to the feed tank wherein the microfiltration unit is configured with a first filter (3) and a second filter (4) for filtering the water;
a nano-filtration membrane assembly (9) comprising
atleast two anionic nanofiltration membranes connected to the microfiltration unit wherein the nano-filtration membrane assembly receives filtered water from the microfiltration unit;
wherein permeate stream from the nano-filtration membrane assembly has TDS content reduced by atleast 80%;
optionally, a chemical precipitation unit (12) connected to the nano-filtration membrane assembly to receive reject stream from the nano-filtration membrane assembly, configured with
a first settling tank (V01), and
a second settling tank (V03), to obtain water with chloride content reduced by atleast 80%.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
In order that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure where:
Figure 1 illustrates a schematic representation of the system for reduction of TDS in feed water.
Figure 2 illustrates process flow diagram for membrane filtration.
Figure 3 illustrates membrane mechanism for salt removal in the nano-filtration membrane.
Figure 4 illustrates process flow diagram of the chemical precipitation unit.
Figure 5 illustrates chloride concentration variation in the permeate from the nano-filtration unit at the Trans membrane pressure drop of 0.5 kg/cm2.
Figure 6 illustrates chloride concentration variation in the permeate from the nano-filtration unit at the Trans membrane pressure drop of 1 kg/cm2.
The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION OF THE DISCLOSURE
The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the description of the disclosure. It should also be realized by those skilled in the art that such equivalent system and method do not depart from the scope of the disclosure. The novel features which are believed to be characteristic of the disclosure, as to method of operation, together with further objects and advantages may be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the figures and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a method that comprises a list of acts does not include only those acts but may include other acts not expressly listed or inherent to such method. In other words, one or more acts in a method proceeded by “comprises… a” does not, without more constraints, preclude the existence of other acts or additional acts in the method.

As used herein, the phrase integrated process refers to a process composed of multiple sub-processes.

As used herein, the term ‘treatment’ refers to the act of subjecting a feed of water to the process of the instant disclosure with the intention of reducing Total Dissolved Solids content in said feed.
As used herein, the abbreviation ‘TDS’ represents ‘Total Dissolved Solids’ and refers to any minerals, salts, metals, cations or anions dissolved in water.
As used herein, the abbreviation ‘MCF’ where used refers to the ‘Micro-cartridge Filter’ present in the system of the instant invention.
As used herein, the term ‘feed’ refers to water introduced into a system or process of the instant disclosure for reduction of TDS. Water fed at each treatment step in the system is referred to as ‘feed’ for that step.
As used herein, the phrase ‘filtered water’ makes reference to the water coming out of the microfiltration unit, wherein said unit removes suspended solids and oil from the water filtered through said unit.
As used herein, the term ‘permeate’ refers to the fraction obtained after completion of filtration through a filtration membrane. It is the part of the feed that passes through the membrane or the fraction which passes through the membrane to yield water with reduced content of impurities.
In the instant disclosure, the term permeate has been used to refer to water obtained after each of the following stages of filtration/purification: Nanofiltration membrane assembly; and chemical precipitation unit; wherein, in the chemical precipitation unit water of increased purity obtained after each stage of purification through a first settling tank, a second settling tank and additional microfiltration membranes has been referred to as ‘permeate’ emerging from the respective units.
As used herein, the phrase ‘reject stream’ refers to the part of the feed stream that is left after separation from the permeate wherein said reject stream contains impurities removed from the permeate.
The present disclosure relates to an integrated process for water treatment.
Particularly, the present disclosure provides an integrated process for reducing Total Dissolved Salt (TDS) content of water by at least 80%, wherein said process comprises steps of:
subjecting the water provided as feed to microfiltration to obtain filtered water; followed by subjecting the filtered water to nanofiltration through anionic nanofiltration membrane to obtain a permeate stream and a reject stream, wherein the TDS content of the permeate stream is reduced by at least 80% when compared to the feed and optionally subjecting the reject stream to chemical precipitation, wherein chloride content of water from the reject stream is reduced by at least 80%.
In an embodiment of disclosure, the microfiltration step in the integrated process of the present disclosure is further, is a cross flow a multi-step filtration process comprising at least a first and a second filtration step.

In said microfiltration step of the integrated process, the filtration is selected from a group comprising:
pressure sand filtration; and
micro cartridge filtration,
or a combination thereof.

Preferably, the microfiltration step of integrated process comprises a combination of pressure sand filtration; and micro cartridge filtration, which together target removal of suspended solids in the water.

Further, in said microfiltration step of the integrated process, permeate from the first filtration step is subjected to the second filtration step. However, before being subjected to the second filtration step, the permeate from the first filtration step is subjected to anti-scalant dosing and acid dosing. The anti-scalant delays reaction between calcium, magnesium and bicarbonates which inhibits the scale formation on the membrane of the subsequent nanofiltration unit, thus increasing life of the nanofiltration membrane. The acid dosing ensures maintenance of neutral pH to ensure effective removal of contaminating ions such as chloride, since negative charge of the subsequent anionic nanofiltration membrane is maintained at neutral pH.
In an embodiment of the disclosure, the pressure sand filter is subjected to intermediate wash through a back-wash line inturn connected to common drain that draws water from a water body. This allows the filter cake to be washed during back washing which increases the life of membrane in comparison to the conventional dead-end filtration.
Though the microfiltration step of the integrated process may be carried out by using the conventional pressure sand filtration and micro cartridge filtration units, a person skilled in the art will appreciate that the dimensions/specifics of the filters employed make all the difference to ensure the desired levels of filtration. Accordingly, the size of sand particles in the pressure sand filter of the instant disclosure must be about 12 microns. This ensures removal of oily material, turbidity and suspended solids from the water fed to the microfiltration unit. Further, the said removal is facilitated with minimum pressure drop across the filter. On the other hand, length of the micro-cartridge filter employed in the present disclosure ranges from about 5 inches to 40 inches and its porosity is of about 150 microns.
In an embodiment of the disclosure, pressure drop across the filter in the microfiltration step ranges from about 1 bar to 5 bar.
As mentioned above, once the feed water is subjected to the step of microfiltration, the water obtained is filtered of all suspended particles. This filtered water is then subjected to nanofiltration through anionic nanofiltration membrane to obtain permeate with reduced TDS as compared to the feed.
Further, like the microfiltration step, the nanofiltration is also a multi-step process comprising at least 2 nanofiltration steps, wherein filtration is performed through an anionic membrane in a nanofiltration assembly unit. The anionic nanofiltration membrane employed at each of the 2 or more nanofiltration steps is same and the filtration is a cross flow filtration. Further, the anionic nanofiltration membrane has pore size of about 0.4nm.
The anionic membrane employed in the nano-filtration step works on the principle of Donnan Exclusion, whereby the membrane becomes charged when placed in a solution and an interaction takes place between the membrane and a charged component. When membranes having ionic groups on their polymer structure are placed in a salt solution, equilibrium occurs between the membrane and the solution. Because of the presence of the fixed membrane charge, the ionic concentrations in the membrane are not equal to those in the solution. The counter-ion (opposite sign of charge of the fixed charge in the membrane) concentration is higher in the membrane phase than in the bulk solution, while the co-ion (same sign of charge as the fixed membrane charge) concentration is lower in the membrane phase. A potential difference at the interphase, called Donnan potential, is created to counteract the transport of counter-ions to the solution phase and of co-ions to the membrane phase. When a pressure gradient across the membrane is applied, water is transported through the membrane. The effect of the Donnan potential is to repel the co- ion from the membrane. Because of electroneutrality requirements, the counter-ion is also rejected and salt retention occurs.
The anionic membrane working on the principle of Donnan Exclusion, thus eliminates negative ions such as sulphate, chloride etc, due to the negative charge of the membrane surface. Simultaneously, to maintain electro neutrality, positive ions also get rejected. Exclusion of ions based on said principle finally causes removal of monovalent and di-valent salts such as calcium chloro aluminate and calcium sulpho aluminate.
As briefly mentioned above, the anionic nanofiltration membrane employed in the present disclosure has pore size of about 0.4nm. The higher pore size of the membrane as compared to the membrane employed in reverse osmosis (RO) allows more water to pass through. It causes increase in permeate flux to about 25 L/hr/m2 to 30 L/hr/m2.
A general comparison between conventional RO technique and the nanofiltration step of the present disclosure is provided below:
Table 1:
Parameters Conventional RO Membranes Anionic Nanofiltration Membrane of the disclosure
Pore Size 10-4 microns 10-3 microns
Charge No charge Negative
Recovery % 40% 80%
Membrane Life Low(1yr) High (2yrs)
Energy Requirement 10x x
Operation cost High (6-7 paisa/L) Low (3-4 paisa/L)
From the above table it is clear that the anionic nanofiltration membrane of the disclosure provides a number of advantages over conventional RO membranes in terms of recovery %, membrane life, energy requirement etc. Said nanofiltration membrane employed in the nanofiltration step of the integrated process of instant disclosure essentially has properties intermediate between reverse osmosis and ultrafiltration membranes. The nanofiltration membrane offers advantages such as low operating pressure, high flux and retention value equivalent to reverse osmosis. In an embodiment, the retention value ranges from about 75% to 80%. Further, the higher pore size of the membrane decreases transmembrane pressure across the membrane to about 10atm to 20atm, thus requiring less pressure than reverse osmosis to filter the water. Said requirement of reduced pressure enables removal of contaminating ions with reduced energy consumption than methods known in the art such as reverse osmosis and multi effect evaporation.
The anionic nanofiltration membranes, by the mechanism described above, repel chloride ions in the feed from the microfiltration unit (filtered water) and allow water to pass as permeate. The permeate obtained after each step of nanofiltration has chloride ion content reduced by at least 30%, generally in the range of about 38% to 40%.
In an embodiment of the present disclosure, permeate from the nano-filtration step has TDS content reduced by about 80% as compared to the water prior to being subjected to treatment by the integrated process. Said permeate is fit for industrial re-use. In certain embodiments, said permeate from the nanofiltration step is subjected to pH correction to maintain neutral pH before being recycled for industrial application, by alkali dosing. In a non-limiting embodiment, the alkali for alkali dosing is sodium hydroxide (NaOH).
In certain embodiments, in the integrated process of the disclosure, reject stream from the nano-filtration membrane assembly is subjected to further treatment by chemical precipitation. Said reject stream generated after membrane filtration contains almost 4 times salt concentration of feed provided to the system.
Said chemical precipitation step that the reject stream from the nanofiltration unit is subjected to, is a two-step process comprising:
a first settling step; and
a second settling step.
The first settling step takes place in a first settling tank and the second settling step takes place in a second settling tank.
The reject stream from the nanofiltration step is subjected to the first settling step by addition of lime and sodium aluminate, along with a flocculant. The lime and the sodium aluminate are prepared in separate agitated tanks connected to the first settling tank. Said agitated tanks are in-turn connected to a water supply to facilitate preparation of the reagent stocks at required concentration. The flocculant is added through a dosing pump. Proper dosing rate and the input water flow rate are set as per the residence time maintained in the first settling tank.
In a non-limiting embodiment, the flocculant is a polyamine based flocculant.
Contents of the first settling tank are subjected to agitation. Slurry is then allowed to settle, and the permeate is passed on for being subjected to the second settling step.
In an embodiment, permeate from the first settling step is subjected to the second settling step to allow further settling of slurry.
Both the first and the second settling steps comprise addition of acetic acid for pH adjustment.
In all embodiments of the present disclosure, slurry from both the first and the second settling steps is solid sludge. Said solid sludge has moisture content of less than 5% and alumina content of about 7% to 9%.
In an embodiment of the disclosure, permeate from the second settling step is further passed through additional filter(s) selected from a group comprising pressure filter, cartridge filter or any combination thereof. Said filters trap particles having size ranging from about 5 micron to 10 micron.
The permeate from the additional filter(s) has suspended solid level of less than about 30 NTU to 50 NTU. Obtained permeate is crystal clear and is fit for industrial re-use.
The chemical precipitation step for treatment of reject stream from the nanofiltration membrane assembly results in precipitation of monovalent and divalent salts as calcium aluminium salts selected from calcium chloro-aluminate or calcium sulpho-aluminate or a combination thereof, from said reject stream.
In an embodiment, the permeate from the nano-filtration step has chloride content reduced by about 70% to 75%; silica content reduced by about 70% to 99%; sodium content reduced by about 65% to 70%; and sulphate ion content reduced by about 80% to 97%, when compared to the feed.
In a further embodiment, the chemical precipitation step reduces silica content in the reject stream from the nano-filtration step by atleast 80%; and sulphate ion content in the reject stream by atleast 80%.
The water with reduced TDS content produced by the integrated processes of the present disclosure is fit for industrial use, such as the water used in the quenching of coke.
As quenching water generally contains more than about 2000 ppm chloride concentration, when quenched coke is heated in the blast furnace, it leads to formation of chloride vapours which cause corrosion of steel structures such as gas cleaning pipelines, pumps etc. and hence those are subjected to change very frequently, even twice in a year. Said problem is overcome by efficient removal of chloride ions from quenching water, which is facilitated by the integrated process of the present disclosure.
Further, high alumina content of solid sludge generated during chemical precipitation step of the integrated process of the present disclosure makes it suitable to use as a coating material in the paint industry.
In all embodiments, the integrated process of the present disclosure is a continuous process and is executed without any interruption.
The present disclosure further provides a system for reducing Total Dissolved Salt (TDS) content of water, said system comprising:
a feed tank (1) connected to a water inlet (0);
a microfiltration unit connected to the feed tank wherein the microfiltration unit is configured with a first filter (3) and a second filter (4) for filtering the water;
a nano-filtration membrane assembly (9) comprising
atleast two anionic nanofiltration membranes connected to the microfiltration unit wherein the nano-filtration membrane assembly receives filtered water from the microfiltration unit;
wherein permeate stream from the nano-filtration membrane assembly has TDS content reduced by atleast 80%;

optionally, a chemical precipitation unit (12) connected to the nano-filtration membrane assembly to receive reject stream from the nano-filtration membrane assembly, configured with
a first settling tank (V01), and
a second settling tank (V03), to obtain water with chloride content reduced by atleast 80%.

In a non-limiting embodiment, fluid connection lines between different components of the system is selected from a group comprising pipes, tubes, hoses, and the like.

The feed tank (1) is connected to a water inlet (0) from a source including but not limited to pond, lake, river, sea and lower cooling pond for coke quenching. Alternatively, the inlet receives water emerging from a coke quenching unit, after completion of the quenching process, for the purpose of recycling said water for industrial re-use. Said water from the coke quenching unit has high content of contaminating ions such as chloride.

In an embodiment of the present disclosure, said feed tank (1) is connected to the first filter (3) of the microfiltration unit through a feed pump (2) that pumps feed from outlet of the feed tank to the microfiltration unit.
The first filter (3) and the second filter (4) of the microfiltration unit are selected from a group comprising:
pressure sand filter; and
micro cartridge filter,
or a combination thereof.
In the microfiltration unit, permeate from the first filter (3) is fed to the second filter (4) for further filtration. Feed stream to the second filter is connected to an anti-scalant dosing device (5) and an acid dosing device (6) which add anti-scalant and acid respectively to said feed stream to maintain neutral pH of the feed stream and prevent scale formation on filter membrane in the subsequent nanofiltration membrane assembly.
In a non-limiting embodiment, the second filter (4) of the microfiltration unit is connected to the nanofiltration membrane assembly (9) through a high-pressure pump (7).
Permeate stream from the nano-filtration membrane (9) assembly is connected to a pH correction unit (10) for correcting pH of the permeate. In an embodiment, the pH correction is by alkali dosing. Said permeate having TDS reduced by atleast 80%, after pH correction, is transferred to a storage tank (11). Reject from the nano-filtration membrane assembly is sent as feed to the chemical precipitation unit (12).
The chemical precipitation unit comprises a lime slacker tank (T02), a sodium aluminate tank (T04), an acetic acid tank (T03) and a flocculant dosing pump. Said tanks are connected to the first settling tank. Further, the first settling tank (V01), the lime slacker tank (T02), the sodium aluminate tank (T04) and the acetic acid tank (T03) each comprise an inlet for water supply.
The first settling tank (V01) of the chemical precipitation unit comprises an inlet for the water supply, the feed, the lime, the sodium aluminate, the acetic acid and the flocculant. Said settling tank comprises a stirrer to subject mixture of the feed and the lime, the sodium aluminate and the acetic acid to agitation, before allowing settling of slurry. The first settling tank is connected to a pit (UC) and to the second settling tank (V02) to which the slurry and permeate from the tank are sent, respectively. Connections to both the pit and the second settling tank are through a pressure filter (PF01).
The second settling tank (V02) has inlet for permeate from the first settling tank (V01) and inlet for the acetic acid. High gravity settling occurs in the second settling tank (V02). The said settling tank is connected to a pit (UC) and a pressure sand filter (F01). After allowing settling to occur in the settling tank, slurry is sent to the pit and permeate is sent as feed to the pressure sand filter.

The pressure sand filter (F01) is connected to a pit and a microcartridge filter (T05). Post solid-liquid separation in the pressure sand filter, slurry from the pressure sand filter is sent to the pit and permeate from the pressure sand filter is sent as feed to the microcartridge filter (T05).
In an embodiment of the present disclosure, permeate from the microcartridge filter is sent to a storage tank and has chloride reduced by at least 80% when compared to reject from the nano-filtration membrane assembly. Optionally, said permeate may be sent back into the water source in an effort to curb pollution of the water source.
Fig.1 is an exemplary embodiment of the present disclosure which illustrates a flowchart depicting the system for reducing Total Dissolved Salt (TDS) content of water. The water intended for treatment is fed to the system through an inlet connected to a feed pump (2). The feed pump pumps the feed into the microfiltration unit composed first of a pressure sand filter (3) and then a microcartridge filter (4). The pressure sand filter is subjected to intermediate wash through a back-wash line which is in turn connected to common drain that draws water from a water body. The pressure sand filter is further connected to a microcartridge filter (4), wherein permeate from the pressure sand filter is sent to the microcartridge filter. The stream from the pressure sand filter to the microcartridge filter is subjected to acid dosing and anti-scalant dosing, facilitated by connections to acid dosing unit (6) and anti-scalant dosing unit (5), respectively. Said stream subjected to acid dosing and anti-scalant dosing forms feed for the microcartridge filter, the permeate emerging from which is sent to the nanofiltration membrane assembly (9) through a high-pressure pump. In certain embodiments of the present disclosure, the connection between the microcartridge filter and high pressure pump has an intermediate connection to a Cleaning-in-Process tank (8) to facilitate cleaning and sanitization of the equipment in the course of the process. In the nanofiltration membrane assembly, the filtered feed from the microfiltration unit is subjected to filtration through two or more anionic nanofiltration membranes. Permeate emerging from the nanofiltration membrane assembly is sent to a storage tank (11) post pH correction facilitated by connection of the permeate stream to a pH correction unit (10). In an embodiment, pH correction is facilitated by alkali dosing. The reject stream from the nano-filtration membrane assembly is connected to a chemical precipitation unit (12). Chemical precipitation of the reject stream from the nano-filtration unit produces a permeate and slurry in the form of solid sludge. The slurry is sent to a pit and the permeate is optionally further connected to a pressure sand filter and/or a microcartridge filter, which yield permeate with TDS reduced by at least 80%.
Fig.4 is an exemplary embodiment of the present disclosure which illustrates a flowchart depicting configuration of the chemical precipitation unit. Reject from the nano-filtration assembly unit is sent to a storage tank (T01). From said tank, the reject is sent as feed stream to a first settling tank (V01). The first settling tank further comprises inlets connected to the lime slacker tank (T02), the sodium aluminate tank (T04), the acetic acid tank (T03), water supply and a flocculant dosing pump, facilitating addition of lime, sodium aluminate, acetic acid and flocculant, respectively, to the feed in the first settling tank. Contents of the first settling tank (V01) is subjected to agitation, following which slurry is allowed to settle. Outlet of the first settling tank is connected to a pit (UC) and second settling tank (V02) through a pressure filter (PF01) wherein permeate from the first settling tank is sent to the second settling tank and the slurry is sent to the pit. The second settling tank receives the permeate from the first settling tank as feed and has an inlet from the acetic acid tank for addition of acetic acid to the feed. Gravitational settling takes place inside the second settling tank (V02). Outlet of the second settling tank is connected to a pit (UC) and a pressure sand filter (F01) wherein slurry after the gravitational settling is sent to the pit and permeate is sent to the pressure sand filter (F01). The pressure sand filter is in-turn also connected to a pit (UC) and a microcartridge filter (T05) wherein slurry from the pressure sand filter is sent to the pit and permeate is sent to the microcartridge filter for final filtration. Permeate from the microcartridge filter has suspended solid level ranging from about 30NTU to 50NTU and is fit for industrial re-use or for discharging into source water body.
In an embodiment, the foregoing descriptive matter is illustrative of the disclosure and not a limitation. Providing working examples for all possible combinations of optional elements in the composition and process parameters is considered redundant.
While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
EXAMPLES
EXAMPLE 1:
Membrane filtration

Water from a pond is fed to the system through the inlet. Inlet pressure (I/L Pressure) for said stream is maintained at 6.5 kg/cm2 and outlet pressure (O/L Pressure) is 5.5 kg/cm2; transmembrane pressure is maintained at about 1.5 kg/cm2 to 2 kg/cm2.
Concentration of ions in the permeate and reject from the nanofiltration membrane assembly is measured and compared with that of the feed. Table 1 provides said comparison.
Table 2: Membrane Filtration
Feed
Permeate Reject
Chloride:1411ppm
Sodium:928ppm
TDS:2167ppm
pH:8.1
SO42-: 176.38ppm
SiO2:1.37ppm
Total Hardness:427.1ppm Chloride:371ppm
Sodium:280ppm
TDS:424ppm
pH:7.2
SO42-: 4.5ppm
SiO2:0.0001ppm
Total Hardness:56.99ppm Chloride:3739ppm
Sodium:2370ppm
TDS:6076ppm
pH:7.5
SO42-: 605.1ppm
SiO2:5.31ppm
Total Hardness:1347.2ppm

As observed from the above data, ion content is drastically reduced in the permeate when compared to the feed. As compared to the feed, content of chloride in the permeate emerging from the nanofiltration membrane assembly unit (preceded by microfiltration step) is reduced by about 73.7%, content of sodium is reduced by about 70%, that of sulphate ion is reduced by about 97.45%, that of silica is reduced by about 99.9% and TDS content is reduced by about 80%. Further, pH of the permeate is restored to near neutral from basic pH of the feed. Overall hardness of water subjected to the process of the present disclosure is reduced by about 86.6% as compared to the feed.
EXAMPLE 2:
Water from a reject stream of membrane treatment is fed to the system through the inlet. Inlet pressure (I/L Pressure) for said stream is maintained at 5.5 kg/cm2 - 4 kg/cm2 and outlet pressure (O/L Pressure) is 2 kg/cm2.
Concentration of ions in the permeate and reject is measured and compared with that of the feed. Table 2 provides said comparison.
Table 3: Chemical precipitation
Sr. No. Parameters Unit Results
Treated
Feed
1. pH Value - 11.41 7.6
2. Total Dissolved Solids mg/L 10182.0 6832.0
6. Chloride (as Cl) mg/L 625.8 3739.0
10. Sulphate (as SO4) mg/L 100.1 605.1
11. Total Hardness (as CaCO3) mg/L, mg/L 1066.0 1347.1
13. Silica (as SiO2) mg/L <1.0 5.31
14. Sodium (as Na) mg/L 6826.0 2370.8
888

As observed from the above data, chloride content in the permeate is reduced by about 83% as compared to the reject from the nano-filtration step, received as feed.

EXAMPLE 3:
Chloride concentration variation at different Trans membrane pressure drops

Trans membrane pressure drop of 0.5kg/cm2
Water from a cooling pond used for coke quenching is fed to the system through the inlet. Inlet pressure (I/L Pressure) for said stream is maintained at 6 kg/cm2 and outlet pressure (O/L Pressure) is 5.5kg/cm2. Transmembrane pressure drop of 0.5kg/cm2 is maintained across the nano-filtration membrane.
Transmembrane pressure drop of 0.5kg/cm2 is maintained across the nano-filtration membrane.
Concentration of ions in the permeate and reject is measured and compared with that of the feed. As evident from figure 5, a significant reduction in chloride concentration is observed in the permeate as compared to the feed.
Trans membrane pressure drop of 1kg/cm2
Water from a _ cooling pond used for coke quenching is fed to the system through the inlet. Inlet pressure (I/L Pressure) for said stream is maintained at 6kg/cm2 and outlet pressure (O/L Pressure) is 5kg/cm2. Transmembrane pressure drop of 1kg/cm2 is maintained across the nano-filtration membrane.
Concentration of ions in the permeate and reject is measured and compared with that of the feed. As evident from figure 6, a significant reduction in chloride concentration is observed in the permeate as compared to the feed.