|Title of Invention||
A METHOD FOR PREPARING FILTER MEDIA FOR REMOVING ARSENIC CONTAMINATION FROM WATER, A FILTER MEDIA, A DEVICE AND A METHOD FOR PURIFYING ARSENIC CONTAMINATED WATER
|Abstract||A method of preparing filter media for removing arsenic contamination (arsenite and arsenate) from water comprising: a. producing rice husk ash by burning rice husk and b. coating rice husk ash with ferric hydroxide - wherein ferric hydroxide is coated on the rice husk ash by adding said rice husk ash to a suspension of ferric hydroxide under agitation, and then separating, drying and if desired powdering the resulting filter media; and - wherein the amount of ferric hydroxide coating on dried filter media ranges from 0.3 to 0.6 mg/gm of rice husk ash; and - wherein said ferric hydroxide suspension is obtained by treating an aqueous solution of a ferric salt with an alkali at a pH range of 3-4; and - wherein the said rice husk ash is agitated with solution of ferric salt such as ferric chloride or nitrate at concentrations of 0.1 - 1 M, preferably 0.5 to 0.7 M and an alkali such as caustic soda (sodium hydroxide), potassium hydroxide or lime (calcium hydroxide) at a pH range of 3-4 and thereafter, the coated ash particles are filtered, dried at 80 - 110 °C and crushed into a powder.|
|Full Text||FORM 2
THE PATENTS ACT 1970
(39 of 1970)
THE PATENTS RULES, 2003
(See Section 10; rule 13)
A Method For Preparing Filter Media For Removing Arsenic Contamination From Water, The Filter Media, A Device And A Method For Purifying Arsenic
TATA CONSULTANCY SERVICES LIMITED
an Indian company having its registered office at 11* floor, Air India Building, Nariman Point, Mumbai - 400021 Maharashtra, India
PREAMBLE TO THE DESCRIPTION The following Provisional specification particularly describes the invention and the manner in which
it is to be performed.
FIELD OF INVENTION
This invention relates to a method for preparing filter media for removing arsenic contamination from water, the filter media, a device and a method for purifying arsenic contaminated water.
Arsenic is a nonmetallic element that comprises 0.00005% of the earth's crust. It is generally transported and distributed in nature through water. The concentration of arsenic in fresh natural water varies widely and primarily depends on the forms in which arsenic occurs in the soil. A major source of arsenic intake by the population is through drinking water. Arsenic can also enter the human body through cereals, fruits and vegetables that have absorbed arsenic containing water. Prolonged exposure to arsenic even in small dosages leads to serious health hazards due to its toxicity and carcinogenicity. Exposure to arsenic leads to alterations in the skin and organs of the respkatory, gastrointestinal, cardiovascular and nervous systems.
Arsenic has been found in groundwater of about 20 countries around the world. Millions of people in India, Bangladesh and Nepal suffer due to acute arsenic poisoning. Recent reports suggest that as many as 450 million people in the Ganges basin could be affected by this deadly element. Arsenic knows no geographical boundaries and newer areas in Asia (including Pakistan, China, Taiwan, Myanmar) are continuously coming under the danger zone.
In natural water, arsenic is present in inorganic forms and exists as two predominant species: arsenate [As(V)] and arsenite [As(III)]. The major arsenic species in surface water is As (V) while As (III) is the dominant arsenic species in groundwater since it is favored under reducing conditions. The concentrations of arsenic in the affected areas generally vary fi-om 80 to 1000 ppb (parts per billion), typically around 200 - 300 ppb. It has been reported that As (III) is more toxic to biological systems than As (V) [Ferguson, J.F. and Davis, J. "A Review of the Arsenic Cycle in Natural Waters", Water Res., 6: 1259 (1972); CuUen, W.R. and Reimer, K.J. "Arsenic Speciation in the Environment". Chem. Rev., 89: 713-764, (1989); Korte, N. E. and Fernando, Q. "A Review of Arsenic (III) in Groundwater", CrU. Rev. Environ Control, 21(1): 1-39 (1991)]. The WHO guidelines for maximum level of arsenic contaminant in drinking water is 10 ppb. The US Environmental Protection Agency (US EPA) sets the drinking water standard for arsenic at less than 10 ppb. In India, the maximum permissible limit is 50 ppb.
Most drinking water treatment processes attempt to remove colour, odour, suspended particles and microorganisms by a variety of processes such as sedimentation, flocculation/coagulation, filtration, disinfection and UV treatment. Unfortunately, these techniques are generally not suited for removal of chemical contaminants such as arsenic. Moreover, most treatment processes are directed at removing arsenate since arsenite is generally non-charged below pH 9.2 and therefore requires a step for converting As (III) to As (V).
Most of the current techniques reported in the literature for the removal of arsenic from drinking water are based on precipitation-coagulation, adsorption, membrane separation and ion exchange [Zeng, L, "Preparation of Iron (III) Oxide Adsorbent for Arsenic Removal ", paper presented at Globe 2002, Vancouver, BC, March 13-15, 2002; Jekel, M.R. "Removal of Arsenic in Drinking Water Treatment", in Arsenic in the Bnvironment, Part I: Cycling and Characterisation, Edited by Jerome O. Nriagu, John Wiley & Sons, Inc., 1994; Kartinen, E.O. (Jr.) and Martin, CJ. "An Overview of Arsenic Removal Processes", Desalination, 103: 78-88 (1995); Bitner, MJ. and Chwirka, J.D. "Arsenic Removal Treatment Technologies for Drinking Water Supplies", Proceeding of 39"' New Mexico Water Conference, 251-255, Albuquerque, N.M., 1994]. In a report by Frey, Michelle M et al. entided "National Compliance Assessment and Costs for the Regulation of Arsenic in Drinking Water", University of Colorado at Boulder, USA, several methods have been evaluated for arsenic removal efficiency and cost. None of the methods described in the report achieved arsenic removal efficiencies greater than 95 percent. The precipitation-coagulation technique is cosdy and thus uneconomical for treatment of small volume of water, typically used in households. The membrane based techniques like reverse osmosis (RO) and electrodialysis (ED) are also very expensive and require infra-structural facilities generally not accessible to the rural population in developing countries. Furthermore, these techniques perform efficiendy when As(III) is first oxidised to As(V) by an oxidising agent. Efficiency of ion exchange can be adversely affected due to the presence of other ions such as sulphate, fluoride and nitrate. Adsorption methods for removal of arsenic are also limited by the type of adsorbents used. For instance, hydrous ferric oxide (FeOOH) can remove both As (V) and As (III). In contrast, activated alumina (AA) is only effective for the removal of As(V).
Some of the arsenic removal filters (for community water supply schemes) use both adsorption and coagulation-flocculation-sedimentation and filtration. The media used for removal of arsenic is crystalline granular ferric oxide, which is relatively expensive. The arsenic
containing water passes through two-stage filtration - in the first stage, a bed of silica is employed to remove iron and in the second stage ferric oxide granules are employed for the removal of arsenic. In certain instances, arsenic containing ground water is pumped into a mixing chamber where oxidising agents like bleaching powder or hypochlorite are added to oxidise As (III) to As (V) and Fe (II) to Fe (III). The water is then sent to another chamber where ferric alum solution is added and mixed with the water. In a clarifier, the hydrolysed product of ferric alum gets flocculated and settles down. Evidentiy, these techniques are based on elaborate flow sheet, require stringent process control and proper maintenance on a regular basis.
A few techniques are also available for household treatment of arsenic contaminated water. For instance, solar oxidation and removal of arsenic (SORAS) is a simple method that uses irradiation of water with sunlight in PET or other UV-A transparent bottles to reduce arsenic levels in drinking water. This technique is based on photochemical oxidation of As (III) followed by precipitation of As(V) on Fe (III) oxides in the presence of a small amount of citrate/lemon juice. Groundwater in Bangladesh contains Fe (II) and Fe (III) and therefore, SORAS could reduce arsenic content at little cost. It can be readily adopted for household level treatment of small quantities of drinking water [Wegelin, M., Gechter, D., Hug, S., Mahmud, A., Motaleb, A.; SORAS - a simple arsenic removal process. Environ Sci Technol, 31, 2005-2011 (1997)].
In the three-kalshi method, a simple filtration assembly consisting of three pitchers is used for removing arsenic from groundwater in Bangladesh. The first kalshi has iron chips and coarse sand, the second kalshi has wood charcoal and fine sand, and the third kalshi is the collector for filtered water. It has been reported that the As (total) can be removed to a concentration below 10 ppb for most samples even at the highest input concentration of 1100 ppb As (total). The dissolved iron concentration decreased from an average 6000 ppb to 200 ppb. pChan A H, Rasul H B, Munir A K M, Habibudowla M, Alauddin M, Newaz S S and Hussam A; Appraisal of simple arsenic removal method for ground water of Bangladesh; J Environ. Sci., A 35(7), 1021 - 1041 (2000)].
A number of processes for removal of arsenic from groundwater have been disclosed in die patent literature — a few of these are described below:
US patent no. 6,461,535 describes a process for removing arsenic from ground water for use in remote dwellings. The process involves contacting water containing arsenic with a
composition comprising clay, a coagulant, and an oxidizer to form a coagulated colloidal mixture, adsorbing the arsenic onto the coagulated colloidal mixmre and separating the water from the coagulated colloidal mixmre. Assistance of skilled personnel is required for handling the speciality chemicals.
US Patent No. 6,368,510 describes a mediod and apparatus for removing arsenic from water at the point of entry or point of use mainly for residential application. The method involves a first stage having a manganese greensand oxidizer to convert arsenite present in the water to arsenate and a second stage for passing the water through an anion exchange resin or a reverse osmosis system. The method involves fairly sophisticated techniques that are generally not implementable in rural areas. Furthermore, the regeneration of the oxidiser and anion exchange resin requires skilled manpower.
US Patent No. 5,575,919 describes a method for removing arsenic from drinking water by using finely divided metallic iron in the presence of powdered elemental sulfur or other sulfur components such as manganese sulfide. This is followed by an oxidation step to effect arsenic recovery as a precipitate which is separated from the water. This method requires a mixing vessel and use of sulfur modified iron, and the addition of acid as well as other chemicals requiring precision monitoring.
The inventions described in these and other patents have many drawbacks such as multiple unit operations, specialised equipment, high initial and operating costs, speciality and expensive chemicals, trained manpower for maintenance of the equipment etc. As a consequence, these solutions are generally not suitable for low-cost implementation in scaled-down versions of arsenic removal filters/devices/processes for individual households.
Metal hydroxide coated sands for removal of multivalent ions especially arsenic from water has been reported [Lukasik, Jerzy (1998), The removal of Microbial and Chemical Contaminants from Aqueous Solutions by Particles Coated with Iron and Aluminium Hydroxides, Ph D Dissertation, University of Florida; Benjamin, M M, Sletten, R S, Bailey, R P, and Bennett, T (1996), Sorption and filtration of metals using iron-oxide-coated sand. Water Research, 30(11), 2609-2620; Joshi, A. alid Chaudhuri, M. (1996), Removal of Arsenic from ground water by iron-oxide-coated sand, ASCE Journal of Environmental Engineering, 122(8),
769-771 and Lo, S., Jeng, H., and Lai, C (1997) Characteristics and adsorption properties of iron-coated sand. Water Sc. Tech., 35(7), 63-70].
Although sand coated with ferric hydroxide does remove arsenic, there is a definite limitation on its performance, which is primarily due to its relatively low surface area. The novelty of our invention lies in employing rice husk ash, in place of sand, as the substrate. The order of magnitude higher surface area of rice husk ash, which is readily available at virtually no cost wherever paddy is grown, significantly enhances the adsorption capacity of the coated filter element. Furthermore, a technological breakthrough for trapping of arsenic on coated rice husk ash was achieved due to an optimized coating procedure adopted in our invention.
Based on our extensive investigations, we disclose in the present application, an invention of a relatively low cost water filter for removal of arsenic (arsenate as well as arsenite) in drinking water. Our invention, which is based on a rural-friendly technology, can be implemented in sufficiently small scale to be suitable for individual households.
OBJECTS OF INVENTION
An object of the invention is to prepare a ferric hydroxide coated rice husk ash based water filter media for removal of arsenic impurities from water, which is simple, efficient and convenient especially for domestic users.
Another object of the invention is to provide a ferric hydroxide coated rice husk ash based water filter, which can remove harmful arsenic from contaminated water regardless of its oxidation state i.e. As (III) or As (V).
Another object of the invention is to provide a ferric hydroxide coated rice husk ash based water filter, which concurrently also filters out harmful bacteria and suspended particles.
Another object of the invention is to provide a method of making ferric hydroxide coated rice husk ash based water filter, which is simple, easy and convenient to carry out and, as such, is eminently suitable for implementation in the rural environment and particularly affordable by the economically depressed class of society.
DETAILED DESCRIPTION OF INVENTION
Rice husk is a perennially renewable agro-waste available at virtually no cost -wherever rice is grown. On combustion, the rice husk ash residue contains 85-95% silica, 4-12% carbon and rest comprising various metal oxides such as alkali, alkaline earth and iron oxides. Because of its crypto-crsytalline or amorphous and highly porous structure, the BET (Brunauer Emmett Teller) surface area of rice husk ash can be as high as 80-100 square meters per gram, depending on the conditions employed for combustion of rice husk. It is easily the cheapest material of large reactive surface area available freely all over the country and around the world. Rice husk ash makes a highly affordable filtering medium par excellence for removal of suspended matter and trapping of bacteria, such as E. Coli, in drinking water. Because rice husk ash is lighter in bulk density and has an order of magnitude greater surface area per unit mass than sand, it acquires when coated with ferric hydroxide, near ideal combination of properties as a filter media with arsenic removal properties.
Rice husk ash may be produced by burning the rice husk in heaps, in a step grate fiarnace or tube-in-basket fTiB) burner [Kapur, P C, (1985) Production of bio-silica from the combustion of rice husk in TiB burner. Powder Tech, 44 pp. 63-67]. It can also be obtained as combustion product from rice husk fired boilers or brick kiln, provided it is free of unbumed husk, wood tars, grit, stones or fused lumps of silica. The average size of the rice husk ash could be either minus 425 plus 212 micron or minus 425 micron. The iron hydroxide coated rice husk ash has a surface area of approximately 50 - 70 square meter per gram. The rice husk ash has at least 80 percent silica, less than 15 percent carbon and more than 10 square meter per gram BET surface area.
Rice husk ash may be coated with ferric hydroxide by contacting ferric hydroxide on to it. Rice husk ash may be added to a suspension containing ferric hydroxide which is obtained by treating a soluble ferric salt solution (for example ferric chloride, ferric nitrate etc.) with a strong alkali eg., caustic soda (sodium hydroxide), potassium hydroxide or calcium hydroxide (lime). Preferably, the pH range of the suspension is 3 - 4. Rice husk ash is added thereto under agitation. The hydroxide coated rice husk ash may be filtered, dried at 80 - 110°C and powdered. The amount of ferric hydroxide coating on dried filter media ranges from 0.3 to 0.6 mg/gm of rice husk ash, preferaljly from 0.4 to 0.5 mg/gm of rice husk ash.
The rice husk ash could also be coated with ferric hydroxide by soaking rice husk ash in a soluble ferric salt solution e.g. ferric chloride or ferric nitrate at concentrations of 0.1-lM, preferably 0.5 to 0.7M followed by in-sitti precipitation using alkali hydroxides.
This invention relates to a filter media for removing arsenic contamination from water comprising rice husk ash substrate having ferric hydroxide coated on the surface thereof
This invention also relates to a device for purifying arsenic contaminated water comprising a housing provided with an inlet and an outlet, and at least one layer of filter media comprising rice husk ash coated with ferric hydroxide positioned in between two water permeable holding means.
This invention also relates to a method of purifying water from arsenic contamination comprising the steps of passing arsenic contaminated water through a filter media of rice husk ash coated with ferric hydroxide and thereafter collecting the water that has been filtered therethrough.
The following examples are illustrative of our invention but not limitative of the scope thereof
112 ml of 2.5 M sodium hydroxide solution was added to 200ml of 0.6M ferric nitrate solution with gentle stirring. The pH of the suspension was in the range of 3 to 4. The sodium hydroxide reacted with ferric nitrate and precipitated ferric hydroxide. To the suspension, 50 gms acid treated boiler RHA (minus 425 plus 212 micron size) was added and soaked for 15 minutes with mild agitation. The contact between the ash and ferric hydroxide precipitate facilitated the coating of the ash particles with hydroxide precipitate. At the end of the contact period, excess liquid from the suspension was filtered off through a Buckner funnel. The filter cake was dried in an oven at 110°C for 4-5 hours. A highly friable dry cake was obtained which was crushed into a powder of ferric hydroxide coated rice husk ash.
20 g of this coated powder was placed in a specially fabricated tapered glass cylindrical column to form a bed of 3.5 cm diameter and 7-8 cm height. A small amount of glass wool and
a thin layer of fine sand were placed at the bottom of the column to hold back the fine coated particles in the filter bed. Another layer of sand was placed on top of the filter bed. Tap water (pH 7 -7.5, conductivity 180-200 mho/cm) was spiked with sodium arsenite to give approximately 250 ppb (parts per billion) concentration of arsenic (III). The spiked water was continuously passed through the filter bed at a flow rate of 2-3 litres/hour and the filtered water in the output stream was monitored for arsenic(III) at regular intervals. After passing 102 litres of arsenic contaminated water through the filter column, the output water showed a concentration of 21 ppb arsenic, considerably below the maximum limit of 50 ppb set by Government of India. The capacity of the coated rice husk ash to trap arsenic was 1.27 mg of arsenic/gm of coated rice husk ash.
The procedure of Example 1 was followed using 118 ml of 2 M sodium hydroxide solution and 200 ml of 0.5 M ferric nitrate solution. The pH of the suspension was maintained at 3. About 50 gm rice husk ash was added slowly with continuous stirring. After settling and filtering as per procedure given in Example 1, the filter cake was oven dried and pulverized into a fine powder of ferric hydroxide coated rice husk ash.
10 gm of the ferric hydroxide coated rice husk ash powder was tested in a filter bed, as described in Example 1 above, to filter 56 litres of arsenate solution containing 250 ppb arsenic(V). The concentration of As(V) in the filtrate (after passing 56 litres) was 23 ppb, much below the specification of 50 ppb set by the Government of India.. The capacity of the coated ash to remove arsenic was 1.4 mg As/gm of coated ash.
The procedure of Examplel was followed using 136 ml of 2.8 M sodium hydroxide solution and 200 ml of 0.7 M ferric chloride solution. The pH of the suspension was maintained at 3. About 50 gm rice husk ash was added slowly widi continuous stirring. After settling and filtering, die filter cake was oven dried and pulverized into a fine powder of ferric hydroxide coated rice husk ash.
' 1. A method of preparing filter media for removing arsenic contamination (arsenite and arsenate) from water comprising:
a. producing rice husk ash by burning rice husk and
b. coating rice husk ash with ferric hydroxide
- wherein ferric hydroxide is coated on the rice husk ash by adding said rice husk ash to a suspension of ferric hydroxide under agitation, and then separating, drying and if desired powdering the resulting filter media; and
- wherein the amount of ferric hydroxide coating on dried filter media ranges from 0.3 to 0.6 mg/gm of rice husk ash; and
- wherein said ferric hydroxide suspension is obtained by treating an aqueous solution of a ferric salt with an alkali at a pH range of 3-4; and
- wherein the said rice husk ash is agitated with solution of ferric salt such as ferric chloride or nitrate at concentrations of 0.1 - 1 M, preferably 0.5 to 0.7 M and an alkali such as caustic soda (sodium hydroxide), potassium hydroxide or lime (calcium hydroxide) at a pH range of 3-4 and thereafter, the coated ash particles are filtered, dried at 80 - 110 °C and crushed into a powder.
2. The method as claimed in claim 1, wherein ferric hydroxide is coated on the rice husk ash by adding alkali to the said rice husk ash soaked in a solution of a soluble ferric salt under agitation, and then separating, drying and if desired powdering the resulting filter media.
'3. The method as claimed in claims 1 and 2, wherein said ferric hydroxide coating is attained by in - situ treatment of the rice husk ash soaked in an aqueous solution of a ferric salt with an alkali at a pH range of 3-4.
4. The method as claimed in claims 1 to 3, wherein the said rice husk ash is obtained by burning its precursor, namely, rice husk in heaps, step grate furnace, brick kiln, tube-in-basket burner or any such suitable combustion device wherein the ash having at least 80 percent silica, less than 15 percent carbon and more than 10 square meter per gram BET surface area.
5. The method as claimed in claims 1 to 4, wherein the amount of ferric hydroxide coating on dried filter media preferably ranges from 0.4 to 0.5 mg/gm of rice husk ash.
6. A filter media for removing arsenic contamination (arsenite and arsenate) from water comprising rice husk ash substrate having ferric hydroxide coated on the surface thereof is obtained by the method as claimed in claims 1 to 5.
7. A filter media as claimed in claim 6, wherein said rice husk ash coated with ferric hydroxide is in powder or cake form.
8. A device for purifying arsenic contaminated water comprising a housing provided with an inlet and outlet means, and at least one layer of filter media consisting of rice husk ash coated with ferric hydroxide positioned in between two water permeable holding means, wherein filter media is as claimed in claims 6 and 7.
9. The device as claimed in claim 8, wherein said rice husk ash coated with ferric hydroxide is in the powder form and the holding means consists of a water permeable fabric or sheet layered with sand positioned below and above said filter media.
10. A filter media for removal of arsenic contamination from water substantially as herein described and exemplified.
11. A device for purifying arsenic contaminated water substantially as herein described and exemplified.
Dated this 9* day of December 2003
Of DePENNING & DePENNING
TATA CONSULTANCY SERVICES LIMITED By their Agent and Attorney
|Indian Patent Application Number||1257/MUM/2003|
|PG Journal Number||42/2008|
|Date of Filing||09-Dec-2003|
|Name of Patentee||TATA CONSULTANCY SERVICES LIMITED|
|Applicant Address||11TH FLOOR AIR INDIA BUILDING, NARIMAN POINT, MUMBAI 400 021,|
|PCT International Classification Number||C 02 F 1/00|
|PCT International Application Number||N/A|
|PCT International Filing date|