[0001] The present invention relates to a method for purification of water. Specifically, the present invention relates to purification of water and, in particular, for removal of fluoride ions from water. The present invention further relates to method for removal of fluoride ions from water using bismuth hydroxide coated rice husk. The present invention provides bismuth coated risk husk as an adsorbent for fluoride ions.

BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Presence of fluoride in groundwater is wide problem as its concentration exceeded the permissible limit at many places. High concentration (>1.5 mg/L) of fluoride ground water is unfit for drinking purpose because it can interfere with carbohydrates, lipids, proteins, vitamins and minerals. Dental and skeletal fluorosis is among very common problems which occur due to high concentration of fluoride intake through drinking water. Because of this threat, Bureau of Indian Standard (BIS) has prescribed range from 1.0 mg/L to 1.5 mg/L of fluoride in drinking water as desirable and permissible limits, respectively. World Health Organization (WHO) has also set up a guideline value of 1.5 mg/L for fluoride in drinking water. The problem is aggravated due to the lack of appropriate and user friendly defluoridation technology. Adsorption, ion exchange, precipitation, electrodialysis and reverse osmosis are some common techniques of fluoride removal water. Amongst the known techniques, adsorption technique is considered among most effective, economically feasible as well as environmentally reliable defluoridation techniques. Several fluoride removal techniques are reported in the literature amongst which the Nalgonda technique and use of activated alumina have been studied extensively. However a simple, efficient and cost effective technology is not available for widespread use in many affected regions. Defluoridation by adsorption process is the cheapest, simplest, easy to implement for a developing countries. Over the years considerable attention has been devoted to the development of better adsorbents.
[0004] There is, therefore, a need to develop more efficient adsorbents useful for removal of fluoride for purification of water that can overcome deficiencies associated with the known arts.

OBJECTS OF THE INVENTION
[0005] An object of the present invention is to provide new and efficient adsorbent for the removal of fluoride from water that satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.
[0006] Another object of the present invention is to provide method for defluorination of water using adsorbent that provides low cost water purification system.
[0007] Yet another object of the present invention is to provide an adsorbent for defluorination that gives treated water fit for drinking purpose.
[0008] Still another object of the present invention is to provide adsorbent for removal of fluoride from water that can be easily prepared and used.
[0009] Another object of the present invention is to provide adsorbent for removal of fluoride from water, wherein developed media can be regenerated.
[0010] Yet another aspect of the invention is to provide method for removal of fluoride ions from water using bismuth hydroxide coated rice husk.

SUMMARY OF THE INVENTION
[0011] The present invention relates to a method for purification of water. Specifically, the present invention relates to purification of water and, in particular, to removal of fluoride ions from water.
[0012] In one aspect, the present invention relates to method for removal of fluoride ions from water using rice based adsorbent.
[0013] In another aspect, the present invention relates to method for removal of fluoride ions from water using bismuth hydroxide coated rice husk.
[0014] In another aspect, the present invention relates to cost effective defluoridation method that is based on surface modification of rice husk ash (RHA) by coating bismuth hydroxide.
[0015] In still another aspect, the present invention relates to surface modification of rice husk ash (RHA) wherein RHA is obtained by burning rice/paddy husk which is an abundantly available and is an inexpensive raw material.
[0016] In one aspect, the present invention relates to a method for purification of water.
[0017] In another aspect, the present invention relates to a method for purification of water by removal of fluoride ions.
[0018] In still another aspect, the present invention relates to a method for removal of fluoride ions from water by using bismuth hydroxide coated rice husk.
[0019] In yet another aspect, the present invention relates to a method for removal of fluoride ions from water using bismuth hydroxide coated rice husk resulting in water, which is which is substantially free from contaminants, such as, fluorine ions.
[0020] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

DETAILED DESCRIPTION
[0021] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0022] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0023] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0024] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0025] The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.
[0026] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0027] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0028] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing..
[0029] The term, “defluorination” as used herein refers removal of fluoride ions from water and both terms can be used interchangeably.
[0030] The present invention relates to a method for purification of water. Specifically, the present invention relates to purification of water and, in particular, to removal of fluoride ions from water.
[0031] In one embodiment, the present invention relates to method for removal of fluoride ions from water using rice based adsorbent.
[0032] In another embodiment, the present invention relates to method for removal of fluoride ions from water using bismuth hydroxide coated rice husk.
[0033] In another embodiment, the present invention relates to cost effective defluoridation method that is based on surface modification of rice husk ash (RHA) by coating bismuth hydroxide.
[0034] In still another embodiment, the present invention relates to surface modification of rice husk ash (RHA) wherein RHA is obtained by burning rice/paddy husk which is an abundantly available and is an inexpensive raw material.
[0035] In embodiment, the present invention relates to a method for purification of water.
[0036] In another embodiment, the present invention relates to a method for purification of water by removal of fluoride ions.
[0037] In still another embodiment, the present invention relates to a method for removal of fluoride ions from water by using bismuth hydroxide coated rice husk.
[0038] In yet another embodiment, the present invention relates to a method for removal of fluoride ions from water using bismuth hydroxide coated rice husk resulting in water, which is which is substantially free from contaminants, such as, fluorine ions.
[0039] In another embodiment of the present invention, water after passing through the column containing Bismuth hydroxide coated rice husk is free from excess fluoride ions and is fit for drinking, with fluoride ion content in the range of 1.0-1.5 mg/L.
[0040] In another embodiment of the present invention, bismuth hydroxide coated rice husk is prepared by wherein bismuth hydroxide coated rice husk is prepared by the following steps:
a) soaking washed rice husk in bismuth solution for 24h;
b) basification of the solution and stirring resulting in precipitation;
c) collecting the precipitates by filtration;
d) washing with double distilled water; and
e) oven drying at 100 ?C for 24 h to obtain bismuth hydroxide coated rice husk.
[0041] In a preferred embodiment, Bismuth trioxide (Bi2O3) (Molecular weight = 466.0), the starting material is dissolved in 2N HCl to make 0.1 M solution of bismuth trioxide. 500 mL of 0.1M of bismuth solution is mixed slowly with 100 g of washed rice husk and left for 24 hours or proper soaking. Thereafter, 500 mL of 2N NaOH solution is added at 100-120 RPM stirring. After precipitation, the product is thoroughly washed with double distilled water in order to remove all the impurities. The synthesized precipitate is filtered by Whatman 42 filter paper and kept at 100 ?C for 24 h oven drying to obtain 50-70 g of bismuth hydroxide coated rice husk for the removal of fluoride from water.
[0042] In another embodiment of the present invention, Bismuth hydroxide coated rice husk is used to remove fluoride from water, using a filtration column filled with Bismuth hydroxide coated rice husk. When water is passed through this column, the Bismuth hydroxide coated rice husk adsorbs the fluoride ions and water coming out is fit for drinking purpose. The column containing Bismuth hydroxide coated rice husk works via adsorption process.
[0043] In another embodiment of the present invention, a filtration column containing Bismuth hydroxide coated rice husk can be used in any filtration module, for the treatment of fluoride contaminated water.
[0044] In another embodiment of the present invention, the filtration column containing Bismuth hydroxide coated rice husk is usable for 5-10 cycles for removal of fluoride ions from the water.
[0045] In another embodiment of the present invention, the adsorption capacity of the filtration column containing Bismuth hydroxide coated rice huskis around 2 mg/g.
[0046] In another embodiment of the present invention, the method comprising using containing Bismuth hydroxide coated rice husk utilizes Rice husk, which is a waste product, thus helping in the management of a waste.
[0047] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
[0048] The present invention is further explained in the form of following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.
[0049] Example 1: Procedure for purifying Fluoride contaminated water using rice husk coated with bismuth hydroxide.
[0050] Fluoride contaminated water (with an initial concentration 5-10 mg/L) can be used for the treatment using rice husk coated bismuth hydroxide. 50 g of the adsorbent (rice husk coated with bismuth hydroxide) is used to treat 100 mL of contaminated water. A contact time of 3 hours is required to reduce the level of fluoride up to drinking water standards (1.0-1.5 mg/L). Afterwards, pH of the treated water is measured to ensure the portability of treated water. pH of water should be in the range of drinking water i.e., pH of 6.5-8.5.
[0051] The foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.

ADVANTAGES OF THE PRESENT INVENTION
[0052] The present invention provides a novel adsorbent for removal of fluoride ions from water that satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.
[0053] The present invention provides a method for removal of fluoride ions from water using an adsorbent which leads to low cost purification of water.
[0054] The present invention provides a rice based adsorbent for removal of fluoride ions from water that can be easily prepared and used.
[0055] The present invention provides an adsorbent for removal of fluoride ions from water wherein the media can be regenerated.
[0056] The present invention provides an adsorbent for removal of fluoride ions from water using bismuth hydroxide coated rice husk wherein the water obtained is fit for drinking purposes.

Claims:1. A method for purification of water by removal of fluoride ions using rice based adsorbent.
2. The method as claimed in claim 1, wherein the adsorbent is bismuth hydroxide coated rice husk.
3. The method as claimed in claim 1, wherein the de-fluoridation method is based on surface modification of rice husk by coating with bismuth hydroxide.
4. The method as claimed in claim 1, wherein water obtained after treatment with bismuth hydroxide coated rice husk is substantially free from contaminants and contains fluoride ions in the range of 1.0-1.5 mg/L.
5. The method as claimed in claim 1, wherein bismuth hydroxide coated rice husk is prepared by the following steps:
a) soaking washed rice husk in bismuth solution for 24h;
b) basification of the solution and stirring resulting in precipitation;
c) collecting the precipitates by filtration;
d) washing with double distilled water; and
e) oven drying at 100 ?C for 24 h to obtain bismuth hydroxide coated rice husk.
6. The method as claimed in claim 1, wherein bismuth hydroxide used for coating the rice husk is prepared from bismuth trioxide.
7. The method as claimed in claim 1, wherein rice husk is obtained by burning rice/paddy husk which is an abundantly available and is an inexpensive raw material.
8. The method as claimed in claim 1, wherein a filtration column filled with Bismuth hydroxide coated rice husk is used to remove fluoride from water.
9. The method as claimed in claim 1, wherein the adsorption capacity of the column containing Bismuth hydroxide coated rice husk is around 2 mg/g.

10. The method as claimed in claim 1, wherein obtained after treatment with bismuth hydroxide coated rice husk is fit for drinking.