DESC:TITLE OF THE INVENTION
A METHOD AND SYSTEM FOR THE REMOVAL OF DISSOLVED CARBON DIOXIDE FROM WATER IN LABORATORY WATER PURIFICATION SYSTEM

FIELD OF THE INVENTION
The invention relates to a method and a system for removing dissolved carbon dioxide from water. The invention particularly relates to a method and a system for removing dissolved carbon dioxide from water to for high purity water applications.
ABBREVIATIONS:
ASTM = American Society for Testing and Materials
SF – Sediment filter
CF – Carbon filter
ACF – Activated carbon filter
RO – Reverse osmosis
DI – Deionization cartridge
UV – Ultra violet purifier
UF – Ultra filtration cartridge
V=Voltage
NRV - Non-return valve

BACKGROUND OF THE INVENTION
Water purification is the removal of undesirable contaminants from raw water. The undesirable contaminants can be chemicals, biological contaminants, suspended solids or gases. There are many known methods for purification of water which reduce the concentration of particulate matter including suspended particles, parasites, bacteria, algae, viruses, fungi, as well as reducing the concentration of a range of dissolved and particulate matter. However during the course of usage the filters get saturated thereby hampering their functions.
The presence of dissolved carbon dioxide in water greatly limits the ability of the water purification system to produce high purity water. These water purification systems typically comprise filtering elements like sediment filter carbon filter, Reverse Osmosis, Ultraviolet purifiers UF filter and De ionization cartridge for removing the dissolved and un-dissolved impurities from water. The life of such filters De Ionization cartridges is drastically reduced by the presence of dissolved carbon dioxide. This is because the dissolved carbon dioxide reacts with water to produce carbonic acid. The dissolved carbon dioxide ionizes in water to form carbonic acid which further ionizes to hydronium ions and bicarbonate ions consequently decreases the resistivity of the water, thus affecting the purity.
Moreover, reverse osmosis membranes do not remove dissolved gases, the carbon dioxide passes through the RO membrane into the permeate stream unimpeded. Thus, the carbon dioxide becomes an undesirable load to downstream polishing mixed beds. Therefore, the RO permeate contains equal amounts of CO2 as generated in the feed water, adding undue ion exchange load on the downstream components to produce high purity water. Further, in the deionizer, the anion resin must remove bicarbonate ions along with the other dissolved anions. In treating water having high alkalinity, a large amount of carbon dioxide is formed as the water encounters cation resin, thus putting a considerable burden on the anion capacity.
Conventionally, the dissolved carbon dioxide is removed by using techniques like aeration, forcing the CO2 out of water by generating low air pressure at the bottom of tower, membrane contractors and chemical dosing method. However, these conventional techniques are typically large, put a lot of moisture into the air and can entrain particles of dirt or contamination in the water. Also some of them require periodic cleaning of the membranes and also need to be sanitized on regular basis; thereby leading to additional maintenance and expertise. Thus, these conventional methods are not suitable for a small scale purpose for producing high purity/ultra-pure water.
Therefore, there is felt a need for a method and a system which is economical and efficiently removes dissolved carbon dioxide from the inlet water without further contamination to provide high purity water having a pre-determined resistivity.

SUMMARY
In an aspect of the present invention, disclosed is a method for sequestering dissolved carbon dioxide from water. The method comprises providing a water feed stream to be purified and passing the water feed stream through the system to obtain water having a pre-determined resistivity. The dissolved carbon dioxide is neutralized by the system.
In another aspect of the present invention, disclosed is a system for sequestering dissolved carbon dioxide from water. The system comprises 30 ml of sodium hydroxide, 100 ml of limestone, 20 ml calcium hydroxide, 100 ml magnesium oxide, 100 ml Ion Exchange Resin and 50 ml marble chips.

BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 depicts a conventional water purification system wherein the system is positioned after the pre-filtration module.
Figure 2 depicts a conventional water purification system wherein the system is positioned after the RO membrane.
Figure 3 depicts a conventional water purification system wherein the system is positioned after the storage water tank.

DESCRIPTION OF THE INVENTION
The present invention discloses a method and a system for sequestering dissolved carbon dioxide from water.
In an aspect of the present invention disclosed is a method for sequestering dissolved carbon dioxide from water. The method comprises providing a water feed stream to be purified and passing the water feed stream to pass through the system to obtain water having a pre-determined resistivity. The system absorbs/ neutralizes the dissolved carbon dioxide from the feed water. The dissolved carbon dioxide is removed before it ionizes in water to form carbonic acid which further ionizes to hydronium ions and bicarbonate ions consequently decreases the resistivity of the water, thereby affecting the purity of the water. The dissolved carbon dioxide is neutralized by reacting calcium carbonate with dissolved carbon dioxide to form soluble calcium bicarbonate; reacting sodium hydroxide with dissolved carbon dioxide to form soluble sodium carbonate; reacting calcium oxide with dissolved carbon dioxide to form calcium carbonate and by reacting calcium hydroxide with dissolved carbon dioxide to form calcium carbonate.
Typically, the water, depending upon the type of the water purification unit, passes through a step of pre-treatment in the sediment filter wherein the particulate matter is filtered out. This filtered water then passes through a chamber of activated carbon where dissolved organics and chlorine is removed from the incoming water. Further the water passes through a RO membrane where 95 - 98 % of ionic and biological impurities are removed. This RO treated water then passes through a pack of ion exchange resin or DI cartridges where majority of ionic impurities are removed by ion exchange resin or DI cartridges. The treated water is then stored in the product water tank (Type-II water). Further this Type II water is then allowed to enter the unit for the final polishing process. The pure water (Type–II) stored in the tank passes through the booster pump (REC Pump) inside the tank to ensure a predictable flow and pressure for UV treatment where complex organics are broken down to simple compounds. UV treated water finally passes through one more pack of ion exchange resin cartridges for final polishing to obtain ultrapure water.
The dissolved carbon dioxide from the inlet water is removed by the system. The system is positioned either after pre-filtration module or after the RO membrane or after storage water tank.
The present invention in another aspect also discloses a system for sequestering dissolved carbon dioxide from water which is system is retrofitted in any conventional water purification systems. The system comprises pre-determined amounts of sodium hydroxide, limestone, calcium hydroxide, magnesium oxide, Ion Exchange Resin and marble chips. The system comprises 30 ml of sodium hydroxide, 100 ml limestone, 20 ml calcium hydroxide, 100 ml magnesium oxide, 100 ml Ion Exchange Resin and 50 ml marble chips.
In an embodiment of the present invention, the sodium hydroxide is in the form of pellets, granules, powder and tablets. In another embodiment of the present invention, calcium hydroxide is in the form of pellets, granules, powder and tablets. In yet another embodiment of the present invention, the Ion Exchange Resin is a strong base anion exchange rein having quaternary ammonium group.
The system is capable of producing water having a resistivity in the range of 1 to 18.2 megaohms. A water feed stream to be purified is passed through the system. The system absorbs/ neutralizes the dissolved carbon dioxide from the feed water. The dissolved carbon dioxide is removed before it ionizes in water to form carbonic acid which further ionizes to hydronium ions and bicarbonate ions consequently decreases the resistivity of the water, thereby affecting the purity of the water.
Calcium carbonate reacts with dissolved carbon dioxide from the feed water/incoming water and forms soluble calcium bicarbonate. This soluble calcium bicarbonate is absorbed by the ion change resin and/or by the RO membrane.
CaCO3 + CO2 + H2O ? Ca(HCO3)2.
Simultaneously, sodium hydroxide reacts with the dissolved carbon dioxide and forms soluble sodium carbonate and water. This dissolved sodium carbonate further dissociates in carbonate ions and water is rejected by the RO membrane.
CO2 + 2NaOH ? Na2CO3 + H2O
CO2 + OH- ? HCO3 - HCO3 - + OH- ? CO3 -2 + H2O
Magnesium oxide (MgO) under humid condition locks CO2 in the form of MgCO3. The below mentioned reaction explains the same.
MgO + H2O ? MgO·H2O*MgO + H2O ? MgO·H2O*
MgO·H2O*+ CO2? MgCO3+ H2OMgO·H2O*+ CO2? MgCO3+ H2O
MgO + CO2? MgCO3
Calcium oxide reacts with carbon dioxide to produce calcium carbonate. The reaction proceeds at room temperature.
CaO + CO2 ? CaCO3
Calcium hydroxide reacts with carbon dioxide to produce calcium carbonate and water.
Ca(OH)2 + CO2 ? CaCO3 + H2O
Sodium hydroxide reacts with the dissolved carbon dioxide and forms soluble sodium carbonate and water. Sodium carbonate further dissociates to form carbonates and water.
CO2 + 2NaOH ? Na2CO3 + H2O
CO2 + OH- ? HCO3 - HCO3 - + OH- ? CO3 -2 + H2O
Calcium carbonate reacts with dissolved carbon dioxide from the feed water/incoming water and forms soluble calcium bicarbonate. This soluble calcium bicarbonate is absorbed by the ion change resin and/or by the RO membrane.
CaCO3 + CO2 + H2O ? Ca(HCO3)2.
The system of the present invention can be configured to be positioned at any place in a water purification unit/system. Typically, at least one system is positioned in the water purification unit/s at the following positions:
- after pre-filtration module;
- after RO membrane; and
- after storage water tank.
In an embodiment of the present invention, the system produces high purity/ultra-pure water.

Figure 1 depicts a conventional water purification system where in the system is positioned after the pre-filtration module.
Figure 2 depicts a conventional water purification system wherein the system is positioned after the RO membrane.

Figure 3 depicts a conventional water purification system wherein the system is positioned after the storage water tank.

NUMBERING OF FIGURES:
1) PRE-FILTRATION MODULE
2) SANITIZATION CELL
3) LOW PRESSURE SWITCH
4) LAB-Q CLEAR FILTER
5) SOLENOID VALVE (TLC,AFT,REC,DISP)
6) BOOSTER PUMP
7) LAB-Q RO MEMBRANE
8) LAB-Q SUPER CARTRIDGE
9) WATER TANK
10) UV LAMP-254 NM FOR TANK
11) AIR FILTER
12) RECIRCULATING PUMP
13) FLOW RESTRICTOR (FR)
14) LAB-Q UV-18
15) RESISTIVITY SENSOR
16) LAB-Q UF FILTER
17) POINT OF USE CAPSULE FILTER
18) NRV
19) SYSTEM

While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.
,CLAIMS:WE CLAIM
1.) A method for sequestering dissolved carbon dioxide from water, said method comprises:
- providing a water feed stream to be purified to pass through a system to obtain water having a pre-determined resistivity;
wherein the dissolved carbon dioxide is neutralized by the system by:
- reacting calcium carbonate with dissolved carbon dioxide to form soluble calcium bicarbonate;
- reacting sodium hydroxide with dissolved carbon dioxide to form soluble sodium carbonate;
- reacting calcium oxide with dissolved carbon dioxide to form calcium carbonate; and
- reacting calcium hydroxide with dissolved carbon dioxide to form calcium carbonate.

2.) The method as claimed in claim 1, wherein said pre-determined resistivity is in the range of 1 to 18.2 megaohms.

3.) A system for sequestering dissolved carbon dioxide from water, said system comprises:
- 30 ml of sodium hydroxide;
- 100ml of limestone;
- 20 ml calcium hydroxide;
- 100 ml magnesium oxide;
- 100 ml Ion Exchange Resin; and
- 50 ml marble chips.

4.) The system as claimed in claim 3, wherein said sodium hydroxide is in the form of pellets, granules, powder and tablets.

5.) The system as claimed in claim 3, wherein said calcium hydroxide is in the form of pellets, granules, powder and tablets.

6.) The system as claimed in claim 3, wherein said Ion Exchange Resin is a strong base anion exchange rein having quaternary ammonium group.

7.) The system as claimed in claim 3, wherein said system is retrofitted in conventional water purification systems.

8.) The system as claimed in claim 3, wherein said system is positioned after the pre-filtration mode or after the RO membrane or after the storage water tank.

9.) The system as claimed in claim 3, wherein said system produces high purity/ultra-pure water.