FIELD OF THE INVENTION:
This invention relates to an arsenic filter using activated laterite.
BACKGROUND OF THE INVENTION:
Contaminated ground water by arsenic is a well-known environmental problem that can have severe human health implications.
There have been worldwide reports of arsenic poisoning of ground water in Bangladesh, in the Mexico, Argentina, Western United States, Taiwan. Also, everyday, arsenic affected areas are discovered in India. An arsenic concentration of 10 ppb has been recommended by World Health Organization as a guideline value for drinking water (WHO, 1993). Depending upon the prevalent redox conditions, arsenic may exist in groundwater both in +3 and +5 oxidation states. As (III) is more toxic in biological systems than As (V). Several studies have demonstrated that arsenic removal can be achieved by various techniques, namely, oxidation/precipitation, Fe electrocoagulation/co-precipitation, alum coagulation/precipitation, lime softening, metal-oxide adsorption using packed beds of activated alumina, granular ferric hydroxide, reverse osmosis and nanofiltration, ion exchange resin, polymer ligand exchange, coagulation-microfiltration etc. Each technology has its own merits and demerits. Among these techniques, reverse osmosis and nanofiltration are promising for arsenic removal, but are energy intensive and more effective in removing As(V) compared to As(III). Therefore, addition of an oxidizing agent is required to oxidize As(III) to As(V) to achieve higher arsenic removal. For ion-exchange resin and polymer ligand exchange, removal of arsenic is high, but the resin medium is costly and the performance of the process is strongly influenced by

the presence of other competing ions, e.g., sulfate, fluoride, nitrate, phosphate, etc. Coagulation, precipitation, lime softening, oxidation, etc. are generally chemical intensive and unsuitable for domestic applications.
In recent years, adsorption by solid is gaining importance due to process simplicity, volume of waste and ease of waste disposal. Various adsorbent like activated alumina, iron coated sand have been commercially available and applied as As-adsorbents. The pre- oxidation of As (III) to As (V) can improve the arsenic removal efficiency but is costlier with respect to a natural adsorbent. The adsorption capacity decreases with increase in pH value and phosphate content in the solution. Adsorbents like, hydrous ferric oxide, granular ferric hydroxide, etc. can remove both As(III) and As(V) ions from aqueous solution. However, most of these oxides are available only in fine powder or generated in situ as gel or suspension in aqueous solution and therefore, are inconvenient in large-scale practical application causing difficulties in separation of solid and liquid. The iron oxides, thus generated are unsuitable as filter medium due to their low hydraulic permeability. Although the use of ores and minerals, namely, kaolinite, hematite and feldspar, etc. have been observed to adsorb arsenic, extensive study in this regard is necessary.
In India, some work on arsenic removal has been reported but most of them remain in the research state. Moreover, the attempt to convert the research output into a low cost easily operable device for rural use is missing. Adsorption of arsenic by natural laterite and ferruginous manganese ores are attempted, but the adsorption capacity towards arsenic species is moderate and need to be modified for practical application.

Therefore, the need exists, for a low-cost, easily operable device which can remove arsenic from ground water.
OBTECTS OF THE INVENTION:
It is therefore an object of this invention to propose an arsenic filter using acid activated laterite.
It is a further object of this invention to propose an arsenic filter, which is easy to operate and maintain.
Another object of this invention is to propose an arsenic filter, which does not require the use of electricity and is cheap.
Yet another object of this invention is to propose an arsenic filter, which can remove other heavy metal ions, fluoride, bacteriological contamination together in a single unit.
A further object of this invention is to propose an arsenic filter, which has an extremely long life.
A still further object of this invention is to propose an arsenic filter, in which after exhaustion of the filter, the filter medium can be safely dumped without any risk of leaching and further contamination.
These and other objects and advantages of the invention will be apparent to the reader on reading the ensuing description, when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig 1: Schematic of domestic filter
Fig 2: Schematic of community scale arsenic filter.
BRIEF DESCRIPTION OF THE INVENTION:
Thus according to this invention is provided an arsenic filter using activated laterite.
In accordance with an exemplary embodiment and without intending to limit the scope of the invention, is disclosed a domestic filter.
The schematics of the domestic filter is presented in Figure 1. It comprises a filter body (1), which is cylindrical in shape and has an inlet (2). It has a height of 75 ± 20 cm and a diameter of 20 ± 5 cm. At the top, in the filter, is housed a distributor plate (3) to evenly distribute the water entering through the water inlet (2), over the entire cross sectional area of the filter. After that there are four layers (4,5,6 & 7) of four different filter medium. Each filter is separated from the next one by a cloth mesh (8). The top layer (4) of raw Laterite has 10±4 cm height. It separates the suspended solids, some amount of Arsenic etc. The next layer (5) is of charcoal and has a height of 10±2 cm. Some dissolved solids, odour and colour of water are removed in this layer. The treated Laterite is placed beneath it and is 35±5 cm thick. This layer (6) is the main Arsenic removing part of the filter. The next and the last layer (7) is of Activated carbon having a thickness of 10±2cm. Bacteria, and other pathogens are removed by this layer. After the last layer, a mesh assembly (9) is placed. The mesh assembly consists of two wire mesh, with a cloth mesh placed between the wire mesh. The purpose of the mesh assembly (9) is to prevent leakage of any filter medium through the outlet (10) at the bottom of the filter. The capacity of the filter is typically 100-150 litres/day.

The activated laterite is prepared by a process comprising of an acid activation process based at optimum operating conditions, followed by an alkaline treatment to neutralize the pH of the material. The detail of the preparation protocol is already filed as a separate patent (614/KOL/2009).
In accordance with an embodiment according to this invention, is disclosed a filter for community scale filtration of water. The filter comprises a layer of sand in addition to the layers described for the domestic filter. The filter comprises 5 layers of different media separated by fine cloth. The first layer comprises raw laterite, the second layer is of charcoal, the third layer is of activated laterite, the fourth layer of sand and the fifth layer is of activated carbon. This filter is used in a community scale filter.
The schematic of the community scale Arsenic filter (11) is depicted in Figure 2. These types of filters are prepared as an assembly of filters (12A-F), each of in the range of 100-150 litres/day. The number of filters in the assembly depends on the water requirement of the community. A typical community scale filter assembly of 500-600 litres/day capacity is described here. First, the water is pumped from the underground by a pump(13), to an overhead tank(14) of 1500 litre capacity. The outlet (15) form the overhead storage tank, is put at 10±2 inches height from the bottom of the tank, to prevent any sedimentation to go through the outlet towards the filter. The flow of water to and from the overhead tank is controlled by two separate valves (16,17). From the outlet, one 1.5 inch nominal diameter pipe (18) is drawn to a common manifold. The water is distributed out evenly to the five filters. The water-flow to each filter is controlled by separate valves (19A-F). The water flow-rate into the filter is kept constant around 100-150 liter/day. Each filter is 100+5 cm high and 20 + 5 cm diameter. At inlet to every filter, there is a distributor plate (20A-F) to distribute the water evenly in entire cross section.

There are 5 layers (21-25) of different filter media, separated by fine cloth (26). The 15±5 cm high first layer (21) consists of raw Laterite. The contribution of this layer is the separation of suspended solids and partial removal of arsenic. The next layer (22) is of Charcoal and it has a height of 10 + 2 cm. The odour and colour of water is removed in this layer. The 35 ± 5 cm height is filled up with treated Laterite (23). The purpose of this layer is to remove the Arsenic. The next layer is of sand (24) and it is 10 + 2 cm high. The fine granular sand size ranges from 125 micron to 250 micron (3 to 2 in the Krumbein Phi Scale). It is available locally. Any residual solid impurity is filtered by the meshing action of sand. The last layer (25) of activated carbon is of 10±2 cm height. Bacteria are removed in this layer. Residual colour, odour etc., are also removed by this layer. At the bottom of each filter, there is a mesh assembly (26) comprising one fine cloth between two wire meshes, to prevent any filter medium to leak out through the outlet (27). All the outlets (27A-F) from all the filters (12A-F) are connected to a bottom storage tank by pipe (28). The filtered, Arsenic free water is collected in the storage tank (29). The water is taken by the community from the tank by tap fitted to it.
In accordance with a preferred embodiment and without meaning to imply any restriction on the scope of the invention, is provided a filter, the key features of which are as follows.
Removal capacity of arsenic (total) 32.5 mg/g. Arsenic concentration in filtrate is always within the WHO permissible limit for drinking water (10 ppb). The filter is capable to remove iron below the permissible limit in drinking water (1 ppm) and remove more than 98% of pathogenic contaminants. The capacity of

domestic filter is in the range of 40-120 litres/day and for community scale it is in the range of 500-2000 litres/day. The filter does not require any external source of power for domestic filters. The life of the filter is in the range of 2-3 years depending on the concentration of arsenic in ground water.
The physical dimension of the domestic filter is 50"(height) x 15"(diameter). The filter has a unique design of feed water distribution over the bed. The filter bed consists of different layer of materials including bacteriostatic activated carbon, charcoal, fine granular sand, activated laterite and raw laterite. The raw laterite layer has a thickness of 10cm, the charcoal layer has a thickness of 10 cm, the treated lateriate is 35 cm in thickness, and the bacteriostatic activated carbon is a 10 cm thick layer. It is possible to use a sand layer (10cm thick) between the treated lateriate and bacteriostatic activated carbon layer. The cost of domestic filter would be in the range of 1700-2000 rupees.
The filters were tested for their performance 12 filters were deployed and their performance in terms of arsenic and iron are being periodically measured and recorded. The data analysis of some of the results are shown below.
Example 1:
One filter (1) was installed in a house in an area with extreme ground water arsenic contamination in the village Bamangachi, Muktipara, Barasat, North 24 Parganas, West Bengal and the performance over more than two months is presented in Table 1. From Table 1, it is observed that the arsenic concentration in the filtrate is well within the WHO limit of 10 ppb. Total coliform count in feed was 110/100 ml and fecal coliform was 21/100 ml. In the filtrate, these counts were nil. These data demonstrates micro-organism removal capacity of the present filter.


Example 2:
Another filter (II) was installed in a house in Barasat (village Bamangachi, Narkelbagan, Barasat, North 24 Parganas, West Bengal). The performance over more than two months is presented in Table 2. From Table 2, it is observed that the arsenic concentration in the filtrate is well within the WHO limit of 10 ppb.


Example 3:
Another filter (III) is operating at a home in Baruipur (Baruipur, South 24 Parganas, West Bengal). The performance over more than two months is presented in Table 3. From Table 3, it is observed that the arsenic concentration in the filtrate is well within the WHO limit of 10 ppb.

Example 4
The performance of the filter (IV) installed in a home, in Habra (North 24 Parganas, West Bengal), is presented in Table 4. From Table 4, it is observed that the arsenic concentration in the filtrate is well within the WHO limit of 10 ppb.



Example 5
The performance of the filter (IV) installed a home, in Rajarhat (Rajarhat, North
24 Parganas, West Bengal), is presented in Table 5. From Table 5, it is observed
that the arsenic concentration in the filtrate is well within the WHO limit of 10
ppb.

Example 6
The performance of the filter (IV) installed in a home, in Rajarhat (Rajarhat, North 24 Parganas, West Bengal), is presented in Table 6. From Table 6, it is

observed that the arsenic concentration in the filtrate is well within the WHO limit of 10 ppb.

Example 7
There are three filters (VII, VIII, IX) installed in Murshidabad. The locations are Lalgola (VII), Ashram (VIII) (Baharampur) and SP Bunglow (Baharampur) (IX). The performances of the three filters are shown in Table 7. From Table 7, it is observed that the arsenic concentration in the filtrate is well within the WHO limit of 10 ppb.

From the test results, it can be concluded that the filter is very much suitable for field use.
The advantages of the domestic filter according to the invention is that it does not require electricity. Further, both the domestic and community scale filters are extremely cheap compared to available filters, they are suitable for removal of arsenic, iron and bacteriological contamination together in a single unit and the

arsenic concentration of filtrate is always within the WHO drinking water permissible limit (10 ppb), independent of the ground water concentration. The filters have extremely long life i.e. approx 2-3 years depending on the concentration of arsenic in ground water and no regeneration of the adsorbent (filter medium) is required during its lifetime. Upon exhaustion of the filter, the filter medium can be safely dumped without any risk of leaching and further contamination. The operation and maintenance of the filters is also easy.
Removal capacity of arsenic is 32.5 mg/g. The filter is capable of removing iron below the permissible limit in drinking water (1 ppm) and remove more than 98% of pathogenic contaminants. The capacity of domestic filter is in the range of 40-120 litres/day and for community scale it is in the range of 500-2000 litres/day.

WE CLAIM:
1. An arsenic filter comprising a filter body (1) provided with a
water inlet (2) in the top cover, said water inlet (2) being in fluid connection with a distributor plate (3) to evenly distribute the water over the cross-section of the filter;
the filter body (1) containing atleast the following layers, a topmost layer (4) of raw lateriate a second layer of charcoal (5); a third layer of treated larerite(6);
an activated carbon layer (7) the layers resting over a wire mesh assembly, and each layer being separated from the next layer by a cloth mesh(8).
2. The arsenic filter as claimed in claim 1 wherein the raw laterite layer has a thickness in the range of 6 to 14 cm.
3. The arsenic filler as claimed in claim 1, wherein the charcoal layer has a thickness in the range of 8 to 12 cm.
4. The arsenic filter as claimed in claim 1, wherein the treated laterite layer has a thickness in the range of 30 to 40 cm.
5. The arsenic filter as claimed in claim 1, wherein the activated carbon layer has a thickness in the range of 8 to 12cm.
6. The arsenic filter as claimed in claim 1, wherein the treated laterite is obtained by the steps of subjecting laterite to acid activation followed by
7. The arsenic filter as claimed in claim 1, wherein a layer of sand is present between the third layer of treated laterite and the activated carbon layer.

8. The arsenic filter as claimed in claim 1, wherein the thickness of the layer of sand is in the range of 8 to 12 cm.
9. The arsenic filter as claimed in claim 7, wherein the sand is finely granulated sand.