Title of Invention	A PROCESS FOR PREPARING ARSENIC FREE (<10 ppb) WATER FROM ARSENIC CONTAMINATED GROUND WATER AND AN EQUIPMENT THEREFOR
Abstract	A process for preparing arsenic free (< 10 ppb) water from arsenic contaminated ground water, characterised in that mixing arsenic contaminated ground water with an homogeneous suspension in aqueous medium essentially containing fine particles of size below 20 µm of arsenic adsorbing media having concentration in the range of less than 5000 ppm, circulating the resultant mixture under pressure in the range of 0.1 to 3 Kg/cm2 through one or more porous ceramic pressure filtration tubes of pore size in the range 1 to 10 µm of the said arsenic adsorbing media

Title of Invention

A PROCESS FOR PREPARING ARSENIC FREE (<10 ppb) WATER FROM ARSENIC CONTAMINATED GROUND WATER AND AN EQUIPMENT THEREFOR

Abstract

A process for preparing arsenic free (< 10 ppb) water from arsenic contaminated ground water, characterised in that mixing arsenic contaminated ground water with an homogeneous suspension in aqueous medium essentially containing fine particles of size below 20 µm of arsenic adsorbing media having concentration in the range of less than 5000 ppm, circulating the resultant mixture under pressure in the range of 0.1 to 3 Kg/cm2 through one or more porous ceramic pressure filtration tubes of pore size in the range 1 to 10 µm of the said arsenic adsorbing media

Full Text	The present invention relates to a process for preparing arsenic free ( Ground water drawn from intermediate acquifers of various parts of West Bengal and Bangladesh was found to contain arsenic above the permissible limit of 0.05 ppm and WHO recommended limit being 0.01 ppm, thereby rendering the water from tube wells and hand pumps unsuitable for drinking purpose. Arsenic contamination of ground water therefore assumed a serious public health issue as ground water serves more than 80 % of the drinking water needs primarily in the rural sector. Reference may be made to various physical and chemical processes for removing arsenic from waste waters for recovery and/or as a pollution abatement measure. Separation can be achieved by arsenic adsorption on amorphous aluminium hydroxide. By such means, as discussed in the Journal of Colloids and Interface Science, volume 54,No. 3,pages 391-399,1976, a plateau of 0.3 ppm arsenic can be attained but further reduction of arsenic content is difficult. It is also known that by precipitation with calcium oxide and ferric chloride, the arsenic concentration in waste water has been reduced from 1000 ppm to 5 ppm as described by J.Hollo et al in Polytech. Chem. Engg. (Budapest)12(3), page 283-292, 1968. Japanese Patent 20952 (1974} .described the use of both slaked lime and bleaching solution together with magnesium chloride for removal of Arsenic(III) from waste water wherein a waste water containing 2490 ppm Arsenic(III) was stirred with these reagents and upon filtering the precipitates, the filtrate had a arsenic content of 3.07 ppm. The US patent 4,201,667(1987) described a process for removing arsenic from aqueous mediums wherein sufficient calcium hydroxide is added in the presence of phosphorous to adjust the pH of the aqueous medium from about 7.0 to 11.5 whereby precipitates of both arsenic and phosphorous are formed and subsequently separated from the aqueous medium. In this process the stirring time was reported to about 30 minutes and separation of the precipitate may be achieved by filtration, settling and decanting, and settling followed by filtration of the supernatant. The arsenic content in the treated water was above 0.01 ppm using this technique. References may also be made to the publications by Prasun Bhattacharyya et. al. and S. Bhattacharyya et. al. in the Proceedings of International workshop on " Control of arsenic contamination in ground water" held on January 5-6, 2000 published by PHED, Govt. of West Bengal, wherein laterite was used as an adsorbent for treatment of arsenic contaminated water. In the above noted proceedings, Prasun Bhattacharyya "et. al. reported that the efficiency varied between 50 - 90 % for 5 gm of • added laterite per 100 ml water under an equilibration period of 20 minutes and S. Bhattacharyya et. al. reported that 0.2 gm laterite ore can absorb 67.4 % and 61.3 % arsenic from 100 ml of 0.27 ppm As(III) or 0.182 ppm of As(V) solution and a shaking time of 5 minutes is found to be optimum for 0.4 gm laterite ore and 100 ml solution of aforesaid concentrations of Arsenic (III or V). References may also be made to the publication of Environmental Systems Information Center, Asian Institute of Technology, March, 1996 on " Drinking water without arsenic: a review of treatment technology", by T. Viraraghavan, K.S. Subramanian and T.V. Swaminathan wherein the advantages and disadvantages of various technology options were described. The conventional techniques for treatment of arsenic contaminated water are primarily based on chemical treatment or co-precipitation technique and adsorption technique which have been tested under field conditions using ground water containing arsenic in the range of 0.1-1 ppm level and arsenic level in the treated water was found to be above WHO recommended limit of 0.01 ppm of arsenic content in drinking water. The co-precipitation technique suffers from the disadvantages like controlling the dose of chemicals, ineffective mixing of chemicals and contaminated water, slower settling rate of the fine particles of precipitating materials, inefficient filtration of fine particles by slow or rapid sand filter due to which the efficiency of arsenic removal is lower particularly in the higher concentration range of arsenic[ above 0.5 ppm] in the contaminated water and the arsenic content after treatment is higher than the WHO recommended limit of 0.01 ppm of arsenic in drinking water. The drawbacks of the activated alumina adsorption technique are insufficient contact time, coating of alumina grains by fine particles of iron present in raw water thereby reducing the efficiency of adsorption and necessity of frequent back washing, shifting the problem of water pollution to soil contamination which is of more serious concern to environmental pollution particularly in the vicinity of treatment plant. Critical analysis of the existing arsenic removal methods and equipments revealed that there is a definite need for improvement in producing safe drinking water as per recommendation of WHO. The main object of the present invention is to provide a process for preparing arsenic free ( Another object of the present invention is to provide an equipment for producing arsenic free ( Another object of the present invention is to provide an equipment for disposal of arsenic enriched sludge generated after treatment of contaminated water. Yet another object of the present invention is to provide an equipment wherein provision for periodical cleaning of ceramic filters is incorporated to enable regeneration and reuse. Accordingly the present invention provides a process for preparing arsenic free ( In an embodiment of the present invention the arsenic adsorbing media used for making the suspension may be such as hydroxides, oxy-hydroxides, phosphates, hydrogen phospate, ammonium phosphates of iron, aluminium, manganese, calcium, magnesium, zinc. In fig. 1 of the drawing accompanying these specification the schematic diagram of an embodiment of the equipment for the process of the present invention is shown wherein (1) is the mixing tank, (2) is the suspension containing arsenic adsorbing media, (3) is the pump, (4) is the pressure filtration module, (5) is the porous ceramic pressure filtered water outlet, (8) is the pressure regulating valve, (9) is the inlet for arsenic contaminated ground water to be treated, (10) is the valve between the mixing tank and pump, (11) is the feed back spray, (12) is porous candle filter for entrapping arsenic enriched sludge. Accordingly the present invention provides an equipment for the process described above for preparing arsenic free ( (10) being connected through a pump(3) to a feed back spray (11) to the mixing tank (1) and one or more pressure filtration modules (4), each of the said modules (4) housing one or more ceramic pressure filtration tubes(5) encased in such a manner so as to allow discharge of the filtered water through an outlet (7), the said pressure filtration module being also provided with a feed back connection (8) to the said mixing tank (1). In an embodiment of the present invention, the porous ceramic pressure filtration tubes may be of pore size in the range of 1 to 10 µm having a predating (6) of thickness at least 10 µm of the arsenic adsorbing media (2). In another embodiment of the present invention, the porous ceramic pressure filtration tubes may be prepared using the process as described in claim in our co-pending patent application no.351DEL2001. In still another embodiment of the present invention, there may be provided a porous candle filter for entrapping saturated arsenic enriched sludge. The steps of the process of the present invention are 1) A suspension of fine particles in water was taken in a container. 2) Several arsenic media precoated porous ceramic tubes were housed in a steel tube fitted with inlet and outlet pipes to form a filter module. 3) Arsenic contaminated water was added to the aqueous suspension of fine particles and the mix was pumped through the filter module under a pressure of 0.1 - 3 Kg/cm using cross flow filtration technique to produce filtered water. The equipment of the present invention may be cleaned as follows : 1) When the fine particles are not able to adsorb arsenic species any more the suspension was pumped through candle filters housed separately under normal atmospheric pressure to entrap the arsenic enriched particles for disposal after cementation within hollow blocks. 2) When the dynamic coating of the fine particles over the inner wall of the porous ceramic tubes are also exhausted, the tubes may be allowed to dry out for about a week for detachment of the dried layer due to formation of mud cracks and flushed with clean water prior to application of a fresh coating layer. 3) When the porous ceramic tubes due to prolonged usage are blocked it may be necessary to rinse with 0.1 to 5 N solution of hydrochloric acid and sodium hydroxide followed by washing with clean water. The novelty of the process and equipment of the present invention lies in successfully removing arsenic to a level below 10 ppb from arsenic contaminated ground water to make safe drinking water. The novelty of the invention in achieving below 10 ppb level of arsenic is much better than the prescribed BIS limit of 50 ppb arsenic and better than WHO recommended limit of 10 ppb arsenic in drinking water. The above said novelty has been achieved by the following inventive steps : 1) Treating arsenic contaminated ground water by mixing with an homogenous suspension of arsenic adsorbing media. 2) Circulating under pressure the mix of contaminated water and arsenic adsorbing media suspension through porous ceramic pressure filtration tubes which are precoated with the arsenic adsorbing media. The following examples are given by way of illustration of the process and equipment of the present invention and should not be construed to limit the scope of the present invention. Example - 1 A mixing tank of 10 litre capacity was taken . 600 ml of 1200 ppm suspension of ferric hydroxide of less than 20µm size in ground water was prepared. The suspension was added to the mixing tank having an outlet connected with a pump of 1/4 HP capacity with the discharge rate of 30 litre per minute. The discharge end of the pump was connected with a porous ceramic pressure filtration tube of 10 mm outer diameter and 300 mm length. The other end of the ceramic tube was connected with stainless steel tube through a pressure gauge and a valve which was connected with the mixing tank. The pressure filtration tube was encased with a leak proof transparent plastic tube in such a manner that there is no leakage at the junction points and the filtered water was obtained through the outer surface of the pressure filtration tube. The suspension of ferric hydroxide is passed through the tube for about one hour to form a coating of more then 10 µm thickness of ferric hydroxide in the inner wall of the tube. 1200 ml of 7.5 ppm arsenic solution in the form of sodium arsenate was added to the ferric hydroxide suspension to maintain 5 ppm arsenic and 400 ppm of ferric hydroxide in the slurry. The slurry was pumped through a pressure filtration tube at a pressure of 2 Kg / cm" and the filtered water was collected . The arsenic content of the filtered water was determined by atomic absorption spectrometry and it was found to be below its detection limit ( Example-2 A mixing tank of 10 litre capacity was taken . 200 ml of 720 ppm suspension of aluminium hydroxide of less than 15 µm size in ground water was prepared. The suspension was added to the mixing tank having an outlet connected with a pump of 1/4 HP capacity with the discharge rate of 30 litre per minute. The discharge end of the pump was connected with a porous ceramic pressure filtration tube of 10 mm outer diameter and 300 mm length. The other end of the ceramic tube was connected with stainless steel tube through a pressure gauge and a valve which was connected with the mixing tank. The pressure filtration tube was encased within a leak proof transparent plastic tube in such a manner that there is no leakage at the junction points and the filtered water was obtained through the outer surface of the pressure filtration tube. The suspension of aluminium hydroxide is passed through the tube for about one hour to form a coating of more then 10 µm thickness of aluminium hydroxide layer in the inner wall of the ceramic tube. 1300 ml of 7 ppm arsenic solution in the form of sodium arsenate was added to the aluminium hydroxide suspension to maintain 5 ppm arsenic and 200 ppm of aluminium hydroxide in the slurry. The slurry was pumped through a pressure filtration tube at a pressure of 1.5 Kg / cm2 and the filtered water was collected . The arsenic content of the filtered water was determined by atomic absorption spectrometry and it was found to be below its detection limit ( Example - 3 A mixing tank of 10 litre capacity was taken . 400 ml of suspension in ground water containing 200 ml of 2700 ppm ferric hydroxide of less than 20 µm and 200 ml of 2700 ppm aluminium hydroxide of less than 15 urn size was prepared . The suspension was added to the mixing tank having an outlet connected with a pump of 1/4 HP capacity with the discharge rate of 30 litre per minute. The discharge end of the pump was connected with a porous ceramic pressure filtration tube of 10 mm outer diameter and 300 mm length. The other end of the ceramic tube was connected with stainless steel tube through a pressure gauge and a valve which was connected with the mixing tank. The pressure filtration tube was encased within a leak proof transparent plastic tube in such a manner that there is no leakage at the junction points and the filtered water was obtained through the outer surface of the pressure filtration tube. The suspension of ferric hydroxide and aluminium hydroxide is passed through the tube for about one hour to form a coating of more then 10 um thickness of layer containing ferric hydroxide and aluminium hydroxide in the inner wall of the ceramic tube. 1400 ml of 6.5 ppm arsenic solution in the form of sodium arsenate was added to the suspension of ferric hydroxide and aluminium hydroxide to maintain 5 ppm arsenic and 300 ppm of each of ferric hydroxide and aluminium hydroxide in the slurry. The slurry was pumped through a pressure filtration tube at a pressure of 2 Kg / cm2 and the filtered water was collected . The arsenic content of the filtered water was determined by atomic absoiption spectrometry and it was found to be below its detection limit ( Example - 4 A mixing tank of 50 litre capacity was taken. 4 litre of 900 ppm suspension of ferric hydroxide of Example - 5 A mixing tank of 1000 litre capacity was taken . 300 litre of 4000 ppm suspension of ferric hydroxide of found to be below 10 ppb. The filtration rate was found to be about 1.5 litre per min. After running the equipment for about three months the suspension was passed through the porous candle filter to entrap the saturated arsenic enriched sludge. The filter module containing ceramic pressure filtration tubes was allowed to air dry and coating layer was washed with deionised water to clean the ceramic tubes and make it ready for reuse. We Claim: 1. A process for preparing arsenic free ( water, characterised in that mixing arsenic contaminated ground water with an homogeneous suspension in aqueous medium essentially containing fine particles of size below 20 µm of arsenic adsorbing media having concentration in the range of less than 5000 ppm, circulating the resultant mixture under pressure in the range of 0.1 to 3 Kg/cm2 through one or more porous ceramic pressure filtration tubes of pore size in the range 1 to 10 µm of the said arsenic adsorbing media. 2. A process as claimed in claim 1 wherein the arsenic adsorbing media for making the suspension are selected from hydroxides, oxy hydroxides, phosphates, hydrogen phosphate, ammonium phosphates of iron, aluminum, manganese, calcium, magnesium, zinc. 3. An apparatus for the process as claimed in claims 1-2 which comprises a mixing tank (1) essentially containing a suspension of arsenic adsorbing media (2) such as herein described, the said tank having an inlet (9) for the arsenic contaminated ground water to be treated, and an outlet (10) for discharge, the aid outlet (10) being connected through a pump (3) to a feed back spray (11) to the mixing tank (1) and one or more pressure filtration modules (4), each of the said modules (4) housing one or more ceramic pressure filtration tubes encased in such a manner so as to allow discharge of the filtered water through an outlet (7), the said pressure filtration module being also provided with a feed back connection (8) to the said mixing tank (1) 4. An apparatus as claimed in claim 3 wherein the arsenic adsorbing media (2) used is selected from porous ceramic pressure filtration tubes of pore size in the range of 1 to 10 µrn. 5. A process for preparing arsenic free ( substantially as herein described with reference to the examples.

Full Text

The present invention relates to a process for preparing arsenic free ( Ground water drawn from intermediate acquifers of various parts of West Bengal and Bangladesh was found to contain arsenic above the permissible limit of 0.05 ppm and WHO recommended limit being 0.01 ppm, thereby rendering the water from tube wells and hand pumps unsuitable for drinking purpose. Arsenic contamination of ground water therefore assumed a serious public health issue as ground water serves more than 80 % of the drinking water needs primarily in the rural sector.
Reference may be made to various physical and chemical processes for removing arsenic from waste waters for recovery and/or as a pollution abatement measure. Separation can be achieved by arsenic adsorption on amorphous aluminium hydroxide. By such means, as discussed in the Journal of Colloids and Interface Science, volume 54,No. 3,pages 391-399,1976, a plateau of 0.3 ppm arsenic can be attained but further reduction of arsenic content is difficult.
It is also known that by precipitation with calcium oxide and ferric chloride, the arsenic concentration in waste water has been reduced from 1000 ppm to 5 ppm as described by J.Hollo et al in Polytech. Chem. Engg. (Budapest)12(3), page 283-292, 1968.
Japanese Patent 20952 (1974} .described the use of both slaked lime and bleaching solution together with magnesium chloride for removal of Arsenic(III) from waste water wherein a waste water containing 2490 ppm Arsenic(III) was stirred with these reagents and upon filtering the precipitates, the filtrate had a arsenic content of 3.07 ppm.

The US patent 4,201,667(1987) described a process for removing arsenic from aqueous mediums wherein sufficient calcium hydroxide is added in the presence of phosphorous to adjust the pH of the aqueous medium from about 7.0 to 11.5 whereby precipitates of both arsenic and phosphorous are formed and subsequently separated from the aqueous medium. In this process the stirring time was reported to about 30 minutes and separation of the precipitate may be achieved by filtration, settling and decanting, and settling followed by filtration of the supernatant. The arsenic content in the treated water was above 0.01 ppm using this technique.
References may also be made to the publications by Prasun Bhattacharyya et. al. and S. Bhattacharyya et. al. in the Proceedings of International workshop on " Control of arsenic contamination in ground water" held on January 5-6, 2000 published by PHED, Govt. of West Bengal, wherein laterite was used as an adsorbent for treatment of arsenic contaminated water. In the above noted proceedings, Prasun Bhattacharyya "et. al. reported that the efficiency varied between 50 - 90 % for 5 gm of
•
added laterite per 100 ml water under an equilibration period of 20 minutes and S. Bhattacharyya et. al. reported that 0.2 gm laterite ore can absorb 67.4 % and 61.3 % arsenic from 100 ml of 0.27 ppm As(III) or 0.182 ppm of As(V) solution and a shaking time of 5 minutes is found to be optimum for 0.4 gm laterite ore and 100 ml solution of aforesaid concentrations of Arsenic (III or V).
References may also be made to the publication of Environmental Systems Information Center, Asian Institute of Technology, March, 1996 on " Drinking water without arsenic: a review of treatment technology", by T. Viraraghavan, K.S. Subramanian and T.V. Swaminathan wherein the advantages and disadvantages of various technology options

were described. The conventional techniques for treatment of arsenic contaminated water are primarily based on chemical treatment or co-precipitation technique and adsorption technique which have been tested under field conditions using ground water containing arsenic in the range of 0.1-1 ppm level and arsenic level in the treated water was found to be above WHO recommended limit of 0.01 ppm of arsenic content in drinking water. The co-precipitation technique suffers from the disadvantages like controlling the dose of chemicals, ineffective mixing of chemicals and contaminated water, slower settling rate of the fine particles of precipitating materials, inefficient filtration of fine particles by slow or rapid sand filter due to which the efficiency of arsenic removal is lower particularly in the higher concentration range of arsenic[ above 0.5 ppm] in the contaminated water and the arsenic content after treatment is higher than the WHO recommended limit of 0.01 ppm of arsenic in drinking water.
The drawbacks of the activated alumina adsorption technique are insufficient contact time, coating of alumina grains by fine particles of iron present in raw water thereby reducing the efficiency of adsorption and necessity of frequent back washing, shifting the problem of water pollution to soil contamination which is of more serious concern to environmental pollution particularly in the vicinity of treatment plant.
Critical analysis of the existing arsenic removal methods and equipments revealed that there is a definite need for improvement in producing safe drinking water as per recommendation of WHO.
The main object of the present invention is to provide a process for preparing arsenic free (
Another object of the present invention is to provide an equipment for producing arsenic free ( Another object of the present invention is to provide an equipment for disposal of arsenic enriched sludge generated after treatment of contaminated water.
Yet another object of the present invention is to provide an equipment wherein provision for periodical cleaning of ceramic filters is incorporated to enable regeneration and reuse.
Accordingly the present invention provides a process for preparing arsenic free ( In an embodiment of the present invention the arsenic adsorbing media used for making the suspension may be such as hydroxides, oxy-hydroxides, phosphates, hydrogen phospate, ammonium phosphates of iron, aluminium, manganese, calcium, magnesium, zinc.
In fig. 1 of the drawing accompanying these specification the schematic diagram of an embodiment of the equipment for the process of the present invention is shown wherein (1) is the mixing tank, (2) is the suspension
containing arsenic adsorbing media, (3) is the pump, (4) is the pressure filtration module, (5) is the porous ceramic pressure filtered water outlet, (8) is the pressure regulating valve,
(9) is the inlet for arsenic contaminated ground water to be treated, (10) is the valve
between the mixing tank and pump, (11) is the feed back spray, (12) is porous candle
filter for entrapping arsenic enriched sludge.
Accordingly the present invention provides an equipment for the process described above for preparing arsenic free ( (10) being connected through a pump(3) to a feed back spray (11) to the mixing tank (1)
and one or more pressure filtration modules (4), each of the said modules (4) housing one
or more ceramic pressure filtration tubes(5) encased in such a manner so as to allow
discharge of the filtered water through an outlet (7), the said pressure filtration module
being also provided with a feed back connection (8) to the said mixing tank (1).
In an embodiment of the present invention, the porous ceramic pressure filtration tubes may be of pore size in the range of 1 to 10 µm having a predating (6) of thickness at least 10 µm of the arsenic adsorbing media (2).
In another embodiment of the present invention, the porous ceramic pressure filtration tubes may be prepared using the process as described in claim in our co-pending patent application no.351DEL2001.
In still another embodiment of the present invention, there may be provided a porous candle filter for entrapping saturated arsenic enriched sludge.
The steps of the process of the present invention are
1) A suspension of fine particles in water was taken in a container.
2) Several arsenic media precoated porous ceramic tubes were housed
in a steel tube fitted with inlet and outlet pipes to form a filter
module.
3) Arsenic contaminated water was added to the aqueous suspension of
fine particles and the mix was pumped through the filter module
under a pressure of 0.1 - 3 Kg/cm using cross flow filtration technique to produce filtered water.
The equipment of the present invention may be cleaned as follows :
1) When the fine particles are not able to adsorb arsenic
species any more the suspension was pumped through
candle filters housed separately under normal atmospheric
pressure to entrap the arsenic enriched particles for disposal
after cementation within hollow blocks.
2) When the dynamic coating of the fine particles over the
inner wall of the porous ceramic tubes are also exhausted,
the tubes may be allowed to dry out for about a week for
detachment of the dried layer due to formation of mud
cracks and flushed with clean water prior to application of a
fresh coating layer. 3) When the porous ceramic tubes due to prolonged usage are
blocked it may be necessary to rinse with 0.1 to 5 N
solution of hydrochloric acid and sodium hydroxide
followed by washing with clean water.
The novelty of the process and equipment of the present invention lies in successfully removing arsenic to a level below 10 ppb from arsenic contaminated ground water to make safe drinking water. The novelty of the invention in achieving below 10 ppb level of arsenic is much better than the prescribed BIS limit of 50 ppb arsenic and better than WHO recommended limit of 10 ppb arsenic in drinking water. The above said novelty has been achieved by the following inventive steps :
1) Treating arsenic contaminated ground water by mixing with an
homogenous suspension of arsenic adsorbing media.
2) Circulating under pressure the mix of contaminated water and arsenic
adsorbing media suspension through porous ceramic pressure
filtration tubes which are precoated with the arsenic adsorbing media.
The following examples are given by way of illustration of the process and equipment of the present invention and should not be construed to limit the scope of the present invention.
Example - 1
A mixing tank of 10 litre capacity was taken . 600 ml of 1200 ppm suspension of ferric hydroxide of less than 20µm size in ground water was prepared. The suspension was added to the mixing tank having an outlet connected with a pump of 1/4 HP capacity with the discharge rate of 30 litre per minute. The discharge end of the pump was connected with a porous ceramic pressure filtration tube of 10 mm outer diameter and 300 mm length. The other end of the ceramic tube was connected with stainless steel tube through a pressure gauge and a valve which was connected with the mixing tank. The pressure filtration tube was encased with a leak proof transparent plastic tube in such a manner that there is no leakage at the junction points and the filtered water was obtained through the outer surface of the pressure filtration tube. The suspension of ferric hydroxide is passed through the tube for about one hour to form a coating of more then 10 µm thickness of ferric hydroxide in the inner wall of the tube. 1200 ml of 7.5 ppm arsenic solution in the form of sodium arsenate was added to the ferric hydroxide suspension to maintain 5 ppm arsenic and 400 ppm of ferric hydroxide in the slurry. The slurry was pumped through a pressure filtration tube at a pressure of 2 Kg / cm" and the filtered water was collected . The arsenic content of the filtered water was determined by atomic absorption spectrometry and it was found to be below its detection limit ( Example-2
A mixing tank of 10 litre capacity was taken . 200 ml of 720 ppm suspension of aluminium hydroxide of less than 15 µm size in ground water was prepared. The suspension was added to the mixing tank having an outlet connected with a pump of 1/4 HP capacity with the discharge rate of 30 litre per minute. The discharge end of the pump was connected with a porous ceramic pressure filtration tube of 10 mm outer diameter and 300 mm length. The other end of the ceramic tube was connected with stainless steel tube through a pressure gauge and a valve which was connected with the mixing tank. The pressure filtration tube was encased within a leak proof transparent plastic tube in such a manner that there is no leakage at the junction points and the filtered water was obtained through the outer surface of the pressure filtration tube. The suspension of aluminium hydroxide is passed through the tube for about one hour to form a coating of more then 10 µm thickness of aluminium hydroxide layer in the inner wall of the ceramic tube. 1300 ml of 7 ppm arsenic solution in the form of sodium arsenate was added to the aluminium hydroxide suspension to maintain 5 ppm arsenic and 200 ppm of aluminium hydroxide in the slurry. The slurry was pumped through a pressure filtration tube at a pressure of 1.5 Kg / cm2 and the filtered water was collected . The arsenic content of the filtered water was determined by atomic absorption spectrometry and it was found to be below its detection limit ( Example - 3
A mixing tank of 10 litre capacity was taken . 400 ml of suspension in ground water containing 200 ml of 2700 ppm ferric hydroxide of less than 20 µm and 200 ml of 2700 ppm aluminium hydroxide of less than 15 urn size was prepared . The suspension was added to the mixing tank having an outlet connected with a pump of 1/4 HP capacity with the discharge rate of 30 litre per minute. The discharge end of the pump was connected with a porous ceramic pressure filtration tube of 10 mm outer diameter and 300 mm length. The other end of the ceramic tube was connected with stainless steel tube through a pressure gauge and a valve which was connected with the mixing tank. The pressure filtration tube was encased within a leak proof transparent plastic tube in such a manner that there is no leakage at the junction points and the filtered water was obtained through the outer surface of the pressure filtration tube. The suspension of ferric hydroxide and aluminium hydroxide is passed through the tube for about one hour to form a coating of more then 10 um thickness of layer containing ferric hydroxide and aluminium hydroxide in the inner wall of the ceramic tube. 1400 ml of 6.5 ppm arsenic solution in the form of sodium arsenate was added to the suspension of ferric hydroxide and aluminium hydroxide to maintain 5 ppm arsenic and 300 ppm of each of ferric hydroxide and aluminium hydroxide in the slurry. The slurry was pumped through a pressure filtration tube at a pressure of 2 Kg / cm2 and the filtered water was collected . The arsenic content of the filtered water was determined by atomic absoiption spectrometry and it was found to be below

its detection limit ( Example - 4
A mixing tank of 50 litre capacity was taken. 4 litre of 900 ppm suspension of ferric hydroxide of
Example - 5
A mixing tank of 1000 litre capacity was taken . 300 litre of 4000 ppm suspension of ferric hydroxide of found to be below 10 ppb. The filtration rate was found to be about 1.5 litre per min. After running the equipment for about three months the suspension was passed through the porous candle filter to entrap the saturated arsenic enriched sludge. The filter module containing ceramic pressure filtration tubes was allowed to air dry and coating layer was washed with deionised water to clean the ceramic tubes and make it ready for reuse.

We Claim:
1. A process for preparing arsenic free ( water, characterised in that mixing arsenic contaminated ground water with an homogeneous suspension in aqueous medium essentially containing fine particles of size below 20 µm of arsenic adsorbing media having concentration in the range of less than 5000 ppm, circulating the resultant mixture under pressure in the range of 0.1 to 3 Kg/cm2 through one or more porous ceramic pressure filtration tubes of pore size in the range 1 to 10 µm of the said arsenic adsorbing media.
2. A process as claimed in claim 1 wherein the arsenic adsorbing media for making the
suspension are selected from hydroxides, oxy hydroxides, phosphates, hydrogen phosphate,
ammonium phosphates of iron, aluminum, manganese, calcium, magnesium, zinc.
3. An apparatus for the process as claimed in claims 1-2 which comprises a mixing tank (1)
essentially containing a suspension of arsenic adsorbing media (2) such as herein described,
the said tank having an inlet (9) for the arsenic contaminated ground water to be treated, and
an outlet (10) for discharge, the aid outlet (10) being connected through a pump (3) to a feed
back spray (11) to the mixing tank (1) and one or more pressure filtration modules (4), each of
the said modules (4) housing one or more ceramic pressure filtration tubes encased in such a
manner so as to allow discharge of the filtered water through an outlet (7), the said pressure
filtration module being also provided with a feed back connection (8) to the said mixing tank
(1)
4. An apparatus as claimed in claim 3 wherein the arsenic adsorbing media (2) used is selected
from porous ceramic pressure filtration tubes of pore size in the range of 1 to 10 µrn.
5. A process for preparing arsenic free ( substantially as herein described with reference to the examples.

Documents:

357-del-2001-abstract.pdf

357-del-2001-claims.pdf

357-del-2001-correspondence-others.pdf

357-del-2001-correspondence-po.pdf

357-del-2001-description (complete).pdf

357-del-2001-drawings.pdf

357-del-2001-form-1.pdf

357-del-2001-form-18.pdf

357-del-2001-form-2.pdf

357-del-2001-form-3.pdf

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Patent Number

231768

Indian Patent Application Number

357/DEL/2001

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

09-Mar-2009

Date of Filing

27-Mar-2001

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	SIBDAS BANDYOPADHYAY	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700032, INDIA.
2	DIPALI KUNDU	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700032, INDIA.
3	SOMENDRA NATH ROY	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700032, INDIA.
4	HIMADRI SEKHAR MAITI	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700032, INDIA.

PCT International Classification Number

C02F 1/62

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA