Arsenic in Groundwater

1. Arsenic in Groundwater • PREAMBLE • A large number of people living in the deltaic regions of West Bengal use water with arsenic concentration in excess of the limit prescribed suitable for human health • The risk involved in such prolonged exposure to arsenic are : spotty pigmentation of skin, keratosis of palms and soles, chronic lung disease, liver fibrosis, peripheral vascular disease, peripheral neuritis and cancer of skin, lung, bladder and liver. • The affected areas confined within the Ganga-Brahmaputra Delta (GBD) expose 30-35 million people in Bangladesh and nearly 6 million people in West Bengal. • New cases of arsenic poisoning in India’s Ganges basin suggests that a crisis in the sub-continent could extend much further than previously thought and a very large population could be exposed to dangerous levels of arsenic in their drinking water. • Currently the primary source of drinking water in rural areas are the domestic tube wells, tapping water from shallow aquifers (50-200 ft). • Studies indicate high arsenic content in water from such shallow aquifers in large parts of the delta. • However, in many areas the deeper aquifers (depth >500 ft) also show arsenic content above the WHO permissible limit of 0.01 mg/l. • Since the first detection of arsenic related diseases in 1980s, regular campaigns are being organised to create general awareness and efforts are made to provide safe drinking water. • The most common measures for providing safe drinking water are : community based on-line filters that work on the principle of arsenic removal by adsorption, oxidation and precipitation by Fe/Al oxides/hydroxides. Clay candle filters are also widely used. • ARSENIC DISTRIBUTION IN GROUNDWATER • Arsenic content in tube wells varies generally from 0.02 - 0.5 mg/l • The tube well depth ranges from 50 - 500 ft, the median depth being 100 ft. • The depth-wise arsenic distribution indicates highest average in 150-170 ft depth zone (Table - 1) • Maximum number of tube wells extract water from aquifers within 50-120 ft depth zone. The aquifers are semi-confined to unconfined and the average arsenic content is ~0.1 mg/l • During development and use of an aquifer, changes may occur in the natural baseline chemistry that may be detrimental to health (e.g. increase in As and F). • Table 1 : Depth-wise arsenic distribution of tube wells • Depth of tube well (ft) As Conc. (Av), mg/l No. of Samples • 50-120 0.11 34 • 150-170 0.23 4 • 230-280 0.09 3 • 350-400 0.13 6 • 450-500 0.09 12 • (*) Source : Current Science, Vol. 86, No. 9, 10 May 2004 Hand pump wells tap into natural accumulations of arsenic • ARSENIC CRISIS DEEPENS • New cases of arsenic poisoning in the Ganges Basin suggest that the crisis in the sub-continent could extend much further than previously thought. • The latest surveys estimate that ~36 million people in the Bengal delta are drinking contaminated water which “may be only the tip of the iceberg”. • The situation in Bihar is alarmingly similar to that of the villages in West Bengal and Bangladesh where hand-pump wells have been dug to provide drinking water. Unfortunately the wells tap into natural accumulations of arsenic swept down from the Himalayas and deposited in the silty aquifers of the Ganges Basin. • (*) Source : http://www.nature.com/news/2003 Arsenic affected areas of West Bengal

2. Installation & Operation of TIPOT Technology PROTOCOL FOR OPERATION OF IN-SITU GROUNDWATER TREATMENT PLANT 1. Check if valve (A) at ground level is closed and air vent pipe valve (5) is open. 2. Open valve (1) on roof top. Keep valve (2) open all the time. Close delivery line sampling valve (B). 3. Close valve (3), (4) and (C). 4. Switch on the main power switch of pump (up position). 5. Push green button on starter panel to run the pump. 6. Note down the time of stating pump. 7. Allow tank to fill for 15 minutes. 8. Open valve (B) and collect 500 ml water sample in sample bottle after washing it with delivery water. 9. Add 0.5 ml of conc. HCl in water sample. 10. Close valve (B). 11. Note down the time when overflow starts. Stop pump. Close valve (1). 12. Open valves (3) and (C) and drain out all the water. Note drainage time. After complete drainage, close valves (C). 13. Start pump again and fill tank. Take sample 15 min before tank fills. Stop pump. Add 0.5 ml of conc. HCL in water sample 14. Close valve (1). 15. Note down the time of stopping the pump. 16. Wait for 30 minutes. Note intermission time in log book. 17. Note down the initial water meter reading. 18. Open valve (4) and note down the time. 19. Allow all water to be recharged into the well. When water flow stops, close valve (4). 20. Note water meter reading. 21. Note time in log book. 22. Repeat the process after 30 minutes intermission [Cycle 2] • INSTALLATION AND COMMISSIOING OF IN-SITU GROUNDWATER TREATMENT PLANT • The TIPOT team visited some of the arsenic affected villages near Kolkata in Sept. 2004 and discussed the possibilities with officials from the National Metallurgical Laboratory (CSIR), Jamshedpur and Ramakrishna Vivekananda Mission Inst. of Advanced Studies (RKVM-IAS), Kolkata. • Based on various technological considerations, the Kashimpur site of RKVM located around 30 km from Kolkata was selected as it already has a tube well with a water delivery rate of ~20 lpm. The location satisfies one important consideration that it has As concentration of around 0.04 mg/l as against the WHO norm of 0.01 mg/l. • Based on the process flow-sheet provided by ISWA, University of Stuttgart, Germany, NML carried out detailed design of the system • The system was installed during March - April 2005 and was commissioned on May 2, 2005. • The demonstration in-situ groundwater treatment plant at Kashimpur is in continuous operation from the day of the commissioning [May 2, 2005]. Photograph of the In-situ Groundwater Treatment Demonstration Plant at Kashimpur near Kolkata

3. Method Merits Demerits Co-precipitation Relatively less expensive, simple chemicals and easily available: Low capital cost: Effective for other contaminants too Problem of disposal of toxic sludge: trained manpower required for operation: Use of different types of chemicals Ion exchange Well defined medium and capacity Expensive medium: Proper maintenance required: Effective only for low sulphate and TDS water. Membrane Technique Well defined medium: Removal efficiency satisfactory: Less space requirement: No solid waste: Effective for other contaminants too High capital cost and running cost: Trained manpower required: Pretreatment of raw water required: Removal of oxidising agent required. Technological Options and the “TIPOT Technology” • LOW COST IN-SITU TECHNOLOGY FOR TREATMENT OF GROUNDWATER • The suggested eco-friendly technology for subterranean (In-situ) treatment of groundwater has been developed at ISWA – Institute for Sanitary Engineering, Water Quality and Solid Waste Management, the University of Stuttgart, Germany, under the leadership of Prof. U. Rott. A conventional tube well fitted with a submersible pump can be used. • A schematic diagram of the process is shown in Figure 1. • By infiltrating oxygen-rich water using the filter pipes of the well, the oxygen concentration and the redox potential of the groundwater in the surrounding area of the well are increased and various physical, chemical and biological processes started or are intensified. • Since the natural aquifer is used as a reactor and a filter, no filter sludge is produced and only a few aboveground facilities are required. • During the delivery of groundwater dissolved arsenic and iron are adsorbed on the surfaces of soil grains, on already existing oxidation products or on bacteria sheets. • The subsequent infiltration of oxygen-rich water into the aquifer causes oxidation of the adsorbed iron and arsenic to precipitate as Fe(III) and As(V). Chemical compounds such as Fe(OH)3 or FeAsO4 are formed, which remain attached to the soil grains.As a result the concentration of As and Fe in the delivery water reduces significantly later. SOME EX-SITU TECHNOLOGICAL OPTIONS FOR TREATING GROUNDWATER • DISADVANTAGES OF EX-SITU OPTIONS FOR • TREATMENTOFGROUNDWATER • In ex-situ treatment, the efficiency of removal of heavy metal varies from 25-95% depending on the technique employed. • In most of the arsenic affected areas, iron content in the groundwater is high and flocculated iron gets deposited on the medium and acts as a base for absorbtion of more arsenic. • However, all these technologies need regular backwash and delay in backwash may lead to malfunctioning of the water purification system. Fig. 1 : Schematic diagram of the in-situ treatment process