Wednesday, 6 May 2015
Low Cost High Quality Arsenic Filter
Patent Filing No.: 430/KOL/2013
Arsenic contamination in groundwater has become a global issue, with more than 200 million are potential at risk, as reported by recent UN report. There are several reasons of arsenic contamination apart from anthropogenic sources which includes (i) use of phosphate fertilizers and pesticides which leaches through the sub-soil and reduces the arsenic binding capacity of the rocks (ii) oxidation of arseno-pyrites present in rocks due to excessive withdrawal of groundwater and (iii) untreated release of industrial effluent and wastes. There are widespread reports of arsenic poisoning of ground water in Bangladesh, Mexico, Vietnam, Western United States, Taiwan, India, Canada and more than 50 countries which entailed above World Health Organization limit for drinking water of 10µg/l. Arsenic poisoning is severe along the Gangetic plains in our country. In certain parts of West Bengal, arsenic concentration as high as 500 to 2000 ppb has also been found. Arsenic is found in +3 and +5 state, both of which are toxic for human health.
Adsorption has been found to be the most suitable mechanism for removal of arsenic. However, the capacity of the adsorbent and its regeneration determines the crux of the problem. Almost all the adsorbents that are available or developed till now require regeneration because of its low capacity, which ultimately releases the arsenic back to the environment, thereby becomes an anthropogenic source. Naturally occurring laterite and ferro-manganese ores exhibits arsenic adsorption. However, the capacity of these materials needs to be increases for practical application.
The work on removal of arsenic using naturally occurring laterite has been initiated in the Department of Chemical Engineering, IIT Kharagpur under the leadership of Prof. Sirshendu De and his students back in 2006. The idea of using laterite came by examining the geographical contamination profile in West Bengal. It was observed that seven districts along the
Ganges (Malda, Murshidabad, Nadia,
South and North 24 Parganas, Part of Burdwan, Kolkata) have been badly affected
by arsenic contamination of groundwater. On the other hand, districts in
south-western and western parts of West Bengal
(Midnapore, Bankura, Purulia) do not have this problem. It has been found that
reason lies in the geological nature of the soil of these regions. The red
colored lateritic rock in these parts contains alumina and iron oxide
components which have a natural capacity to adsorb arsenic species. The present
innovation details with acid activated based laterite adsorbent (Development of
high capacity and cost effective arsenic adsorbent using modified laterite,
Filed 614/KOL/2009) which has high arsenic adsorption capacity (both arsenite
Salient features of the technology
(i) The total removal capacity of arsenic is 32.5 mg/g, which is highest compared to all other available arsenic adsorbents.
(ii) Ultra low cost of the filter media appropriate for the socio-economic conditions of our country. Filtered water can be produced at 2 paisa per liter ($1.2 for 1000 gallons).
(iii) Power is required only to operate the pump to lift water into overhead tank. Flow in the filters is by gravity. In case of household filter, no power required.
(iv) Removal of arsenic, iron and bacteriological contamination together in a single unit. The filter is capable to remove iron below the permissible limit in drinking water (0.3 ppm) and remove more than 98% of pathogenic contaminants.
(v) The filter bed consists of different layer of materials including bacteriostatic activated carbon, charcoal, fine granular sand, activated laterite and raw laterite.
(vi) No interference from sulphate, chloride, magnesium and iron ions are observed.
(vii) Works over wide range of pH 5.5 to 8.0.
(viii) The total arsenic concentration in the filtrate is always less than 10 ppb (WHO limit).
(ix) The filter life 5 years in the worst possible condition. The filter will be more if the influent arsenic concentration is less.
(x) No regeneration or backwashing is needed during its lifetime, which makes this technology unique and unparallel.
(xi) The empty bed contact time is 7.2 hours which is necessary for the adsorption to occur.
(xii) The adsorbent binds arsenic by strong chemisorption. The spent adsorbent meets TCLP protocol and can safely disposed. It can be used for making bricks, road lining, pavements, cell filling, etc. Therefore, this adsorption provides the ultimate solution for treatment of arsenic contaminated water.
(xiii) Easy maintenance and operation.
(xiv) The cost of domestic filter would be in the range of 2500-3000 rupees (40 to 50 USD).
Total number of Household units deployed so far: 16
Lalgola, Mushidabad, West Bengal (one unit in August 2012)
Behrampur, Murshidabad, West Bengal (two units in August 2012)
Baruipur, South 24 Paraganas, West Bengal (one unit in Sep 2012)
Rajarhat, North 24 Parganas, West Bengal (two units in Oct 2012)
Bamangachi, Barasat, North 24 Parganas, West Bengal (one in March 2011 and remaining 8 in Oct 2012)
Habra, North 24 Parganas, West Bengal (one unit in Sep 2012)
Total number of community filters deployed: 3
Kashinathpur free primary school, Rajarhat, North 24 Parganas, West Bengal (installed in Oct 2012) - 500 L/day capacity
Ambika Girls High School, Rajarhat, North 24 Parganas, West Bengal (installed in December 2012) - 1500 L/day capacity
Choudhuar Primary School, Manikchawk Block, Malda, West Bengal (installed in December 2014) - 800 L/day capacity.
The technology has been developed, demonstrated and deployed in field with active support from Department of Science & Technology, Govt. of India and UNICEF, West Bengal. Technology is transferred to one company.
The contributors to this work are –
Sourav Mondal, Barun Kumar Thakur, Kuldeep Yadav, Mrinmoy Mondal, Raka Mukherjee, Anirban Roy, Biswajit Barman and Sirshendu De, Department of Chemical Engineering, IIT Kharagpur.