Title of Invention

AN IMPROVED PROCESS FOR WATER TREATMENT TO REMOVE ARSENIC, IRON AND PHOSPHATE BY ZERO VALENT IRON AND A REACTOR THEREFOR

Abstract

The present invention relates to novel process for treatment of ground water to effect removal of contaminants and pollutants like arsenic, phosphate or iron by co-precipitation and co-oxidation reactions. The present invention also describes reactors therefore that are operable with or without the aid of electric current, the said reactors comprising a zero valent iron unit and a filtration system for ground water treatment. -3 NOV 2008

Full Text

FORM2 THE PATENTS ACT, 1970 (39 of 1970) & The Patents Rules, 2003 COMPLETE SPECIFICATION (See section 10; rule 13) 1. Title of the invention: AN IMPROVED PROCESS FOR WATER TREATMENT TO REMOVE ARSENIC, IRON AND PHOSPHATE BY ZERO VALENT IRON AND A REACTOR THEREFOR. 2. Applicant(s) (a) NAME : (b) NATIONALITY (c) ADDRESS: INDIAN INSTITUTE OF TECHNOLOGY Created by an act of Parliament, Institute of Technologies Act, 1961 Indian Institute of Technology, Bombay, India 3. PREAMBLE TO THE DESCRIPTION The following specification particularly describes the invention and the manner in which it is to be performed: 2336 MUM. 2008 -3 NOV 2008 FIELD OF INVENTION The present invention relates to the development, design and operation of a reactor comprising a zero valent iron unit and a filtration system for water treatment. More particularly it relates to an improved process for removal of metals like arsenic and iron and non metals like phosphate from water with the aid of a reactor comprising a zero valent iron unit. BACKGROUND OF THE INVENTION Multiple methods of water treatment systems are employed to render contaminated water fit for consumption and/or pretreatment of industrial toxic waste water before its disposal in the environment. Natural water resources are limited. Potable drinking water is scarce with increasing population. The ground waters are known to be contaminated with one or more contaminants. For example the ground waters of West Bengal and Bangladesh are heavily contaminated with arsenic. Arsenic removal is necessary to prevent occurrences of arsenic poisoning. Skin lesions, melanosis, hyperkeratosis on the palms and feet, skin cancer and cancer of internal organs are symptoms of arsenic poisoning. Various types of reactors are available for treatment of water. A reactor is an enclosed device that provides specific conditions for mediating and controlling chemical/biochemical reactions. A suitable reactor is selected on the basis of nature, quality, contaminants of ground water, environmental surroundings, and infrastructure and baseline arsenic levels. The type of reactors include batch reactors, plug flow reactors, continuous flow reactors, sequential reactors, etc. These reactors operate on principles of oxidation, precipitation, coagulation, ion exchange, membrane filtration, foam flotation, solvent extraction, etc. Most often reactors are operated on multiple principles involving multiple steps, reagents, and reactions to give potable drinking water. Most of water treatment reactors suffer from one or more drawbacks like production of toxic solid sludge, inefficient treatment, incomplete removal of contaminants, sophisticated operation and 2 maintenance, preconditioning. Moreover the resultant sludge requires treatment prior to disposal. Arsenic, iron, and phosphate are major contaminants of ground water. Arsenic in drinking water is a worldwide concern. Ground waters of Bangladesh and West Bengal in India are heavily contaminated with arsenic. More than 100 million people have been reported to be at risk due to the consumption of arsenic from ground water. Arsenic is a carcinogen and its ingestion deleteriously affects the gastrointestinal tract, cardiovascular system and central nervous system. Due to its high toxic effects United States Environmental Protection Agency (USEPA) lowered the permissible level from 50 ppb to 10 ppb. This drastic reduction of permissible levels in turn requires technology to achieve such minimal levels. There exists serious technological constraint to achieve drinking water with arsenic concentration at permissible level of 10 ppb. High-tech and complex treatment mechanisms have failed in rural areas of India and Bangladesh due to lack of skilled manpower and cost to a larger extent. "On two simple Arsenic removal Methods for Groundwater of Bangladesh" by A. H. Khan, S.B. Rasul et al mentions about a 3- kalshi assembly for arsenic removal. First kalshi has iron chips and coarse sand, the second kalshi has wood charcoal and fine sand and the third kalshi serves as the collector of filter water. This technique however, suffers from drawbacks such as dry bed and bed clogging by hydrous ferric oxide thereby limiting its efficiency. Moreover, this technique does not provide flexibility of scale up to cater larger communities. "Arsenic removal with iron (II) and iron (III) in waters with high silicate and phosphate concentrations" by Linda C. Roberts et al published in the journal "Environmental Science & Technology, volume 38, Issue 1, January 2004, pages 307 to 315" discloses arsenic, silicate and phosphate removal from ground water. The said article elaborates combined effects of partial As (III) oxidation of Fe (II) and simultaneous competitive sorption and co-precipitation of silicate, phosphate, 3 arsenate and arsenite with the forming Fe (III) precipitates. It suggests multiple addition of Fe (II) for enhancement of arsenic oxidation. Multiple addition of Fe (II) is beneficial for (a) As (V) has high affinity for HFO than As (III) and, (b) As phosphate competes with As(V), multiple additions give phosphate a less head start. However, the said prior art does not teach controlled leaching of iron to effect efficient removal of arsenic. Also the aforesaid article is unable to provide drinking water with arsenic concentration less than 10 ppb as per WHO guidelines. It moreover suffers from drawbacks such as low iron oxidation levels, slow7 arsenic removal, and generation of sludge in higher amounts. Also the aforesaid prior art is applicable only at laboratory scale. "Arsenic Removal from Ground water by household sand filters: Comparative field study, model, calculations and health benefit" by Michael Berg et al published in the journal "Environmental Science & Technology, Volume 40, Issue 17, September 2006 pages 5567 to 5573 mentions arsenic removal using sand filters. However, there exists problem of clogging due to formation of hydrous ferrous oxide floccules. The aforesaid prior art gives inconsistent and nonreproducible results. Moreover the said prior art is workable only if the ground water contains sufficient amount of dissolved iron "Oxidation and removal of arsenic (III) from aerated groundwater by filtration through sand and zero-valent iron" by Olivier X. Leupin et al published in the journal "Water Research, volume 39, Issue 9, May 2005, Pages 1729 to 1740" reports oxidation of As (III) to As (V) during oxidation of Fe (II) to Fe (III). However, it has inherent problems with scale up as leaching of Fe (II) tends to reduce with time and moreover the leaching is not controlled. Also the process requires backwashing. The process requires a series of filtrations to achieve removal of arsenic to below 50 ppb. However, the method is unable to achieve arsenic levels of less than 10 ppb as per WHO guidelines. 4 "Removal of arsenic from water by electrocoagulation" by P. Ratna Kumar et al published in the journal "Chemosphere, Volume 55. Issue 9, June 2004, Pages 1245 to 1252" mentions arsenic removal from drinking water by electrocoagulation. Water treatment is carried out with passage of current through iron electrodes. However, the aforesaid article does not provide any teaching on design of the reactor and is limited to laboratory scale in batch mode only. Also the quantity of iron required for arsenic removal is more. US5556545 discloses removal of arsenic species from an aqueous medium with alumina as sorbent. However, US5556545 suffer from limitations requiring regeneration and conditioning of the sorbent and this regeneration process creates a hazardous solution. The sorbent is lost during regeneration process thereby rendering the process economically unfeasible. Most treatment methods for arsenic removal from ground water remove arsenic but residual arsenic concentration exceeds the 0.05 mg/L (drinking water quality standard) in most countries. It has been observed in villages in India and Bangladesh that a highly successful technology may not succeed in rural areas unless it fits into the rural circumstances and is well accepted by the masses with maintenance being done locally. Water treatment technologies suffer from one or more drawbacks, limitations and scope of application. With respect to advantages and disadvantages of available methods of water remediation, none of the treatment method posses all the desirable attributes such as high contaminant- removal efficiency, minimal follow-up treatment, economic feasibility, rapid rate of reaction, low maintenance and ease of operation. The need of the hour is a technology for efficient removal of arsenic without necessity of multiple steps, reagents and reactions in efficient and economical manner without posing any environmental hazard. The ideal technology should be robust and user friendly to meet drinking water requirements of public at a 5 larger scale, a technology that does not require manipulation of pH or pressure under different phases and facilitates efficient removal of arsenic, iron and phosphate. The inventors of present invention have surprisingly invented a reactor that has all the above-mentioned features and achieves efficient removal of metals like arsenic and iron and nonmetals like phosphate. The resultant treated ground water of the present invention meets the stringent WHO guidelines for drinking water. The method of the present invention for the removal of arsenic, iron and phosphorus from ground water obviates the drawbacks of the available technologies such as clogging, incomplete treatment, sludge disposal, etc. OBJECT OF INVENTION It is an object of the present invention to provide an improved process for treatment of water. It is a further object of the present invention to provide a reactor for water treatment. It is another object of the present invention to provide a reactor that works on principle of co-precipitation and co-oxidation. It is further an object of the present invention to provide a reactor for water treatment that uses controlled zero valent iron leaching. It is further an object of the present invention to provide a reactor that achieves efficient oxidation ofarsenite, complete removal of foul odor and produces sludge in lesser amounts and of low toxicity. It is yet another object of the present invention to provide a reactor for water treatment that is robust and facilitates easy up gradation to larger scale. It is further an object of the present invention to provide a reactor that is operable both with and without the aid of electric current. 6 It is further an object of the present invention to provide a process for cleaning the reactor. SUMMARY OF INVENTION According to an aspect of the present invention there is provided a process comprising the steps of: a. Spraying untreated water into the reactor through inlet to affect aeration; b. Passing the aerated water though the zero-valent iron leaching unit to undergo co-precipitation and co-oxidation reactions; c. Passing the water from zero valent iron leaching unit through a gravel filtration bed to effect removal of contaminants and pollutants by a simultaneous process of adsorption on to iron hydroxide and co- oxidation of arsenic and iron; d. Discharging the treated water from the reactor. According to another aspect of the present invention there is provided a novel reactor comprising zero-valent iron leaching unit and filtration medium to bring about co-precipitation and co-oxidation reactions. According to yet another aspect of the present invention there is provided a novel reactor which is operable with and without the aid of electric current. BRIEF DESCRIPTION OF ACCOMPANYING FIGURES Figure 1A illustrates a schematic representation of reactor for removal of contaminants. Figure IB illustrates a schematic representation of reactor for removal of contaminants by electrocoagulation. 7 Figure 2 A shows the setup for column run of arsenic removal unit on laboratory scale. Figure 2 B shows the setup for column run of arsenic removal unit on laboratory scale with aid of ac/dc current. Figure 3 A shows zero valent iron unit with tray-partition (1) and over-flow pipes (2). Figure 3 B shows iron overflow pipe of zero valent iron unit. Figure 4 shows results of column study experiment with 500 ppb arsenic [As(III)] and lppm phosphate dissolved in tap water and lOOOmg zero valent iron added into the filter column. Figure 5 shows results of column study experiment with 1000 ppb As(Iil) and 3 ppm phosphate dissolved in tap water and 2000 mg zero valent iron added into the filter column Figure 6 shows the iron removal pattern obtained in the experiment with 1000 ppb As(IN) & 3 ppm phosphate dissolved in tap water and 2000 mg zero valent iron added into the filter column Figure 7a shows the arsenic removal plant setup for Setup II in a continuous mode. Figure 7b shows results obtained for the arsenic removal unit used for field samples of Setup II. Figure 8a shows the arsenic removal plant setup for Setup I in a continuous mode. 8 Figure 8b shows the results obtained for the arsenic removal unit used for field samples of Setup I. Figure 9 shows results of column study experiment with lOOOppb arsenic dissolved in tap water and 5mg/L iron added electrochemically into the filter column. Figure 10 shows results of column study experiment with lOOOppb As(III) dissolved in SGW and 5.5mg/L iron added electrochemically. Figure 11 Results of column study experiment with 1000 ppb As (III) and 1 ppm phosphate dissolved in SGW and 8.2mg/L iron added electrochemically. Figure 12A shows the results obtained for column run with the simulated field samples in Setup II. Figure 12 B shows the results obtained for column run with the simulated field samples in Setup I. DETAILED DESCRIPTION OF THE INVENTION The present invention is a simple and robust process that uses zero valent iron (ZVI) in a specially designed reactor that ensures good oxygen transfer, separation of hydrous ferric oxide [HFO] floccules formed by Mn-siUf anodic oxidation in a unit operated on electric current, and direct leaching from zero valent iron (ZVI) in a unit operated without electric current followed by use of low cost granular media for removal of contaminants like arsenic, iron, phosphates, etc from water. The reactor of the present invention finds a broad application in ground water treatment, heavily contaminated with arsenic. Arsenic in groundwater is mainly present in the inorganic form as As (III) (arsenite) and As (V) (arsenate). It is well known that As (III) removal is quite difficult and thereby in the conventional 9 processes a chemical oxidant is used to oxidize As (III) to As (V), and then As(V) is adsorbed onto a sorbent along with phosphate. In the removal process herein developed, due to the leaching of iron when in contact with water, iron [Fe(0)] gets dissolved in the form of Fe(II) and under the mild oxidizing environment, Fe(II) gets oxidized to Fe(III) forming high oxidizing intermediates which co-oxidizes As(III) to As(V). Hence, As(III) gets oxidized without addition of chemical oxidant. Further Fe (III) forms insoluble hydrous ferric oxide (HFO) in the pH range 6.5 to 8.3 (which is the pH range of ground water) which adsorbs arsenate (HFO has quite high affinity for As (V) and is separated by the designed filtration chamber. The process developed is quite simple and easy to operate and achieves efficient oxidation of arsenite to arsenate. The reactor of the present invention achieves drinking water standard as per WHO guidelines. The process is surprisingly able to consistently achieve arsenic levels below 10 ppb for initial arsenic concentrations ranging from 300 -1000 ppb. The reactor is able to consistently provide drinking water for 100- 300 families on a daily basis and can be scaled up to cater to much larger communities. The present invention described herein does not require frequent backwashing/ cleaning and therefore has low operation and maintenance requirements. Moreover, it does not require monitoring of flow parameters and is easy-to-operate by unskilled personnel. Zero valent iron unit according to the present invention may either be a zero valent iron contactor tray fitted with overflow pipes on its base in absence of electric current or a plastic tray with mild steel rods connected to AC/DC source such that the rods act as electrodes in electrochemical cell. The system works efficiently between a current density of 0.5 mA/cm2 to 2.0 mA/cm2. Example: A three hundred litre reactor vessel with dimensions of 1.0m X 1.0m X 1.3m (L X B X H) is used. Filtration medium of gravel size of 3 mm to 5mm diameter are used for aeration zone and filtration media. Only the size of gravel and aggregates used at the bottom and top portion (4 cm) ranged between 10mm to 15 mm. There 10 is even distribution of the flow at the inlet of the reactor vessel. The rate of filtration is maintained around 0.9m3/m2/hr. The method consists of ZVI used to leach desired amounts of iron. Drinking water containing up to 1.0 mg/L of arsenic, phosphate concentration of up to 3mg/L and iron concentration of up to lOmg/L at the pH range of groundwater is treated with this technology using 3-20kg ZVI. The iron hydroxide formed from the leaching of ZVI adsorbs the arsenic, iron and phosphate present in the water and is filtered out. The treated water total arsenic concentration is Then the hydrous ferric oxide precipitate along with the adsorbed arsenic, iron and phosphate is filtered out to give drinking water confining with the WHO guidelines for drinking water. In an embodiment as indicated in figure 1 A, the water is introduced from inlet (1) through spray (2) to achieve aeration. Water is then exposed to specially designed zero-valent iron unit (3) through overflow pipes. Water is trickled through gravel filter (4) with gravel size 4-7 mm and gravel filter (5) with gravel size 2-4 mm. The treated water is then let through outlet (6). The reactor may be cleaned through cleaning ports (8a, 8b, 8c and 8d). Drain (7) for servicing and maintenance. In another embodiment as indicated in figure 1 B, the water is introduced from influent inlet (1) through spray (2) to achieve aeration. Water is exposed to zero-valent iron unit (3) connected to electric current source through overflow pipes. Water is trickled through gravel filter (4) with gravel size 4-7 mm and gravel filter (5) with gravel size 2-4 mm. The treated water is then let through outlet (6). The reactor may be cleaned through cleaning ports (8). Drain (7) for servicing and maintenance purpose II Mechanism: Redox reactions occurring at cathode and anode: Anode (Oxidation): Fe (s) + 2 OH" -> Fe(OH)2 + 2 e" Fe(OH)2 +OH" -> Fe(OH)3 +e As033" + 2 OH" -> As043" + H20 + 2e" Cathode (Reduction): 2 H20 + 2 e" -» H2 (g) + 2 OH" Overall: Fe+ As033" + H20 -* Fe(OH)3 (s) + Fe4As2Oii(s) + H2 (g) + OH" The reactor is set up in continuous mode as shown in figure 7A and 8A.. Continuous mode reactor may be employed for more efficient removal of ground water contaminants. Plastic tanks may be employed for economical benefit Components of zero-valent iron reactor: A. Zero-valent iron unit: Ungalvanized iron nails of size ranging from %" to 1" are affixed on iron support medium. The ZVI contactor tray design is represented by figure 3A. It comprises a square tray of 0.9m x 0.9m with overflow pipes covering its entire area. The bottom of the tray is drilled and the overflow pipes are welded to it. The overflow pipe is shown in figure 3B. Each overflow pipe is a hollow pipe of diameter 2.5cm and height of 11.5cm. The height and number of overflow pipes may vary as per the influent water quality. The top opening of the overflow pipe is covered with conical cover, as per the design. This cover should not be higher than 2.0 cm from the tray bottom. The lower 1.3 cm of the overflow pipe is below the tray. All the welds and joints in the tray are made leak proof. The distance of the zero valent iron unit from the filtration bed is in the range of 0.05 m to 0.5 m. 12 B. Filtration chamber: The filtration chamber for separation of hydrous ferric oxide floccules as shown in figure 6. The chamber consists of a tank of dimensions lmxlmx 1.3m. The tank is filled with gravel and aggregates of the size of 2- 4mm up to the height of 0.55m. Then another 0.15m is filled with gravel and aggregates of the size 4- 7mm. The top 0.6m is left free for ZVI unit and inlet pipe. Cleaning ports are present at a distance of 0.70m, 0.55m, 0.40m and 0.25m from the bottom. C. Reactor washing technique: The ZVI unit is first dissembled and the inlet pipe of the reactor vessel dismantled. Then the cleaning port (8) of figure 1A and figure IB is opened. The inlet from water feed is connected to the reactor washing pipe assembly. The reactor washing pipe assembly consists of a flexible pipe which is in-turn connected to a 3' long GI pipe of 3A" diameter. The water is then pumped in with a lift and force hand pump. The GI pipe is pushed in into the clogged filter media. The GI pipe is inserted at different places over the entire cross section. The other cleaning ports are sequentially cleaned. Other reactors require cleaning by backwashing but it is known to be quite ineffective and cumbersome and require frequent backwashing. In this method complete cleaning can be achieved with much less effort and also the dirty wash water can be directed into a collection tank reducing spillage and keeps the surroundings clean. The reactor of the present may be cleaned once in two months. The invention is now illustrated with a few representative but non-limiting examples. WORKING EXAMPLES Example-1 Synthetic solution was prepared containing 500 ppb As (III) and lppm phosphate in tap water. This water sample was passed through the filtration column. Iron was 13 added by leaching 1000 mg ZVI. The results of this experiment are shown in figure 4. Flow rate was 0.9m2/m3/hr. Example-2 Synthetic solution was prepared containing 1000 ppb As (III) and 3mg/L phosphate in tap water. This water sample was passed through the filtration column. Iron was added by leaching 2000 mg ZVI. The results of this experiment are shown in figures 5 and 6. Flow rate was 0.9m2/m3/hr. Example- 3 Column run with simulated field samples: Simulated field samples of the sites, namely Setup I and Setup II were synthesized in the laboratory as per the details in tables 3 and 4. The iron requirement in Setup II sample was 4mg/L and in the Setup I sample was 8.5mg/L. The groundwater iron was utilized to meet some of the iron requirement so actual addition of iron by ZVI leaching at the 2 sites is 2.5mg/L at Setup II and 4.5mg/L at Setup I. Example- 4 Synthetic solution was prepared using lOOOppb As(III) in tap water. And this water sample was passed through the filtration column. 5mg/L Iron was added electrochemically. The results of this experiment are shown in figure 9. Example- 5 Synthetic solution was prepared using lOOOppb As(Hl) in simulated groundwater (as per Table 3) after referring to BGS data. One sample had no phosphate while the second had Ippm phosphate added. And this water sample was passed through the filtration column. 5.5mg/L and 8.2mg/L Iron was added electrochemically. The results of this experiment are shown in figure 10 and figure 11 respectively. 14 Example- 6 Column run with simulated field samples: Simulated field samples were synthesized in laboratory as per the details in table 4. The iron requirement in Setup II sample was 4mg/L and in the Setup I sample was 8.5mg/L. The groundwater iron was utilized to meet some of the iron requirement so actual addition of iron by electrocoagulation at the 2 sites is 2.5mg/L at Setup II and 4.5mg/L at Setup I. Table 3: The composition of simulated groundwater (from British Geological Survey database) and the median Bangladesh groundwater characteristics (from British Geological Survey database): Simulated GW Bangladesh GWa b % wells with [x] > [x]s pH initial 7.0 ± 0.1 7.0 ± 0.2 HCO3 (mM) 8 7.8 ±2.7 45 Ca (mM) 2.5 1.9±1.4 32 Mg (mM) 1.6 1.3 ±0.8 24 Si (mg/L) 30 (1068 uM) 19.2 ± 4.7 2 a Mean values and standard deviations obtained from the British Geological Survey database (values of pH and HCO3" from Special Study Areas; all other values from National Survey Data) using only wells with [As] > 50ppb. b Percentages of wells in the British Geological Survey database with parameter [x] exceeding that of the synthetic groundwater [x]s. Table 4: Arsenic, iron and phosphate concentrations of the waters of the two field sites that were simulated in the laboratory for column run. 15 Site Arsenic Concentration Phosphate Concentration Iron concentration Setup II 250 ug/L 0.33 mg/L 1.5mg/L Setup I 650ug/L l.Omg/L 4.0mg/L Continuous columns were run with these water samples on laboratory scale models using ZVI unit. The column setup used at the 2 sites is shown in figures 7A and 8A. Figures 7B and 8B show results of arsenic removal in waters from the sites of Setup II and Setup I. It can be clearly seen that arsenic levels were brought down to under 10u.g/L in both the sites, and on further running the columns it was noticed that the arsenic in the effluent/ treated water remained below the 10u.g/L level. Continuous columns were run with these water samples on laboratory scale models based on electrocoagulation principle as in figure 2 B. The result of column study is shown in figure 11. Figures, 12A and 12 B show arsenic removal in the waters from the sites of Setup II and Setup I. It can be clearly seen that arsenic levels were brought down to under lOug/L in both the sites. On further running the columns, it was noticed that the arsenic in the effluent/ treated water remained below the 10|^g/L level. Table 5 gives a comparative data on Fe/As ratio obtained by present invention with respect to other technologies. Table 5: Fe/As ratio obtained by present invention in the presence and absence of silicate and phosphate and that obtained by other technologies Sr. No Author/study Chemicals Used Presence of Si/P in ppm Fe/As Ratio 1 Devitreetal, 1991 Fe(0) No 3400 2 Muniretal.,2001 Fe(0) No 1311 16 3 Mengetal., 2001 Hypochlorite-t-Fe(TI) 18/1.9 >40 4 Karschunke et al., 2000 Spiked As(V), Fe(II) No 77.5 5 Leupin and Hug., 2005 Fe(0) 20/2 349 6 Present invention Fe{0) No 4.5 7 Present invention Fe(0) 0/2 10 Example-7 Waste Disposal: The precipitate formed during treatment, waste material were used for toxicity characteristic leaching procedure (TCLP) test to check for possible arsenic leaching from landfills. TCLP tests were with TCLP Extraction fluid 1 and 2 as per USEPA regulations. f The results are tabulated in table 6. Table 6: results of TCLP test of sludge with extraction fluid 1 & 2. TCLP extraction fluid sample no Amt of As leached 1 1 0.098 mg/L 1 2 0.048 mg/L 2 3 0.184 mg/L It is clear from the foregoing description and the analytical data as described above, water filter developed for arsenic removal as disclosed in the present invention is suitable for the treatment of drinking water at community level in affected areas. 17 CLAIMS 1. A process for treatment of ground water comprising the steps of: a. spraying untreated water in to reactor through inlet to affect aeration; b. passing the aerated water though zero-valent iron leaching unit to undergo co-precipitation and co-oxidation reactions; c. passing the water from zero valent iron leaching unit through a gravel filtration bed to effect removal of contaminants and pollutants by a simultaneous process of adsorption on to iron hydroxide and co-oxidation of arsenic and iron; d. discharging the treated water from the reactor. 2. The process for treatment of ground water as claimed in claim 1 wherein step b is effected in the presence of electric current. 3. The process for treatment of ground water as claimed in claim 2 wherein the voltage/current density is in the range of 0.5mA/cm2 to 2.0 m A/cm2 4. The process for treatment of ground water as claimed in claim 1 wherein step b is effected in the absence of electric current. 5. The process for treatment of ground water as claimed in claim 1 wherein the pollutants in step d comprise arsenic, phosphate or iron. 6. A reactor for treatment of ground water which is operable in the absence of electric current and comprising zero valent iron unit, gravel filtration bed. 18 The reactor as claimed in claim 6 wherein the zero valent iron unit comprises iron tray with overflow pipes attached to bottom of the tray and conical covers on overflow pipes. A reactor for the treatment of ground water which is operable in the presence of electric current wherein the zero valent iron unit of the reactor comprises plastic tray with mild steel rods connected to AC/DC source. The reactor for treatment of ground water as claimed in claim 6, claim 7 and claim 8 wherein the distance between the zero valent iron unit and gravel filtration bed is in the range of 0.05 m to 0.5 m. A process of cleaning the reactor claimed in claim 6, claim 7 and claim 8 comprising the steps of: a. opening the reactor cover and removing the zero-valent iron unit, b. connecting the inlet water feed to flexible pipe assembly. c. pushing and inserting the flexible pipe assembly through the clogged filtration bed, opening the cleaning ports sequentially, and; d. directing the dirty wash water to a collection tank. Dated this 3 day of November 2008. Saloni Rastogi Of S. Majumdar & Co. Applicant's agent 19

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