A simple, low-cost filter that removes arsenic and iron from water

  • The technology removes arsenic and iron together from contaminated water at a cost less than one rupee (Re. 0.5) per 100 litres (Rs. 1 for 200 litres).
  • Groundwater overuse has been linked to an upsurge in arsenic levels, but there have not been enough surveys in Assam to fully understand the scale of the problem.
  • Assam lies next-door to the Indian state of West Bengal – one of the worst arsenic-hit states in the country. It also shares the same pattern of distribution and movement of groundwater as Bangladesh, its international neighbour ravaged by the arsenic issue.

Diprupa Bhaktiari is a change-maker in Assam’s arsenic-hit Mazgaon village along the north bank of the Brahmaputra. For over a year, she has been operating a humble filtration unit that delivers arsenic-free drinking water capable of sustaining a small family for a week at a cost of Re. 1.

Bhaktiari has tapped into ‘Arsiron Nilogon’ (arsiron for arsenic and iron; nilogon is the Assamese equivalent for removal), a simple, low-cost technology developed by researchers at Tezpur University, that aims to shield people from the scourge of arsenic.

The technology removes arsenic and iron together from contaminated water at a cost less than one rupee (Re. 0.5) per 100 litres (Rs. 1 for 200 litres).

“We are a village of 83 households and around 400 members. Many villagers started getting the patchy skin hyperpigmentation symptoms of arsenic poisoning. We realised the extent of the problem when the varsity’s team examined the arsenic levels. For over a year now, I have been operating the 200 litre unit. It is easy and very cheap. For a small family, 200 litres is enough for three to seven days,” Bhaktiari told Mongabay-India at a DST workshop in Tezpur University.

Bhaktiari’s unit is one of the six Arsiron Nilogon units (four 200 litre and two units of 500 litre) installed and functional in Mazgaon village, where the Tezpur University team said, it recorded “the highest arsenic concentration in groundwater in Assam at 990 parts per billion (ppb) in a tube well,” way higher than the 50 ppb cap set by the Indian government.

A single Arsiron Nilogon set-up with two tanks. Photo by Sahana Ghosh.

The system comprises two 200 litre or 500 litre plastic drums with taps, perched on bamboo stands, placed one below the other. The top drum is where the chemical action plays out while a sand-gravel bed in the bottom tank extracts the clean water for use.

“It is a two stage process based on oxidation-coagulation-adsorption at optimised pH. It does not require electricity and can be custom-made at home with easily available materials. It is suitable for household and community level settings,” said Robin Dutta, a professor at the department of chemical sciences, Tezpur University, and the inventor of the technology.

The method involves the addition of three common chemicals (baking soda, potassium permanganate, ferric chloride) in specific amounts to the water to be treated, which takes about three minutes, followed by filtration after one hour of resting.

“The recurring cost of the chemicals is less than Re 0.5 per 100 litres of water (Rs 500 for one lakh litres). The capital cost is the cost of two containers, two plastic taps plus some sand and gravel. A household can opt for buckets instead of drums,” explained Dutta.

The patented technology can bring down arsenic concentration from levels as high as 500 ppb to below 2 ppb and iron concentration is reduced to less than 0.1 ppm, he said.

The team kicked-off trials in June 2010 at an arsenic-affected village in Titabor in Jorhat district and in six arsenic-affected schools in different locations in Assam.

M. Nath of North Eastern Regional Institute of Water and Land Management (NERIWALM), who was involved in the third-party evaluation of the technology, said no toxic residue is leftover and the uptick in concentrations of sodium, potassium and chlorine, due to the addition of the chemicals, is insignificant.

“Compared to other methods, such as nano-based technologies, it is cheaper. Also, nanoparticles are potentially carcinogenic,” Nath stresses.

Diprupa Bhaktiari operating Arsiron Nilogon unit in Assam. Photo by Pallabi Sonowal

The minute quantity of solid sludge produced in the aftermath of the treatment, passes the toxicity characteristic leaching procedure (TCLP) test of the US Environmental Protection Agency, said Dutta.

A household system generates approximately 36–50 g of the sludge per year. Users are urged to collect the sludge in earthen pots containing sand with a small hole in the bottom, which can be disposed off safely.

Hydrologist NC Ghosh of the National Institute of Hydrology -Roorkee, believes removal technologies are “stop-gap” arrangements and are welcome, in rural India, where people can’t wait for the “final solution”.

“This particular technology has got some advantages. It is definitely simple and the raw materials are easy to procure and are cheap. The major challenge, as with all such technologies, is ensuring the sludge is disposed off safely. They are not permanent solutions,” Ghosh told Mongabay-India.

Ghosh pressed for in-situ (on site) reduction of arsenic within acceptable limits, through groundwater and aquifer management, by understanding geomorphology and mobilisation processes.

Groundwater overuse and arsenic upsurge

Elevated level of arsenic in groundwater or arsenic contamination is caused largely by natural processes, and partly due to anthropogenic activities like the application of fertilisers, burning of coal, leaching from coal-ash tailings and from mining activity, as per a Standing Committee on Water Resources report 2015-2016.

The presence of arsenic in groundwater in the delta region of the Himalayan rivers (such as Ganges, Brahmaputra and Barak Valley) is ascribed to the sediment that gets washed down from the upland catchments and is deposited in the lowland basins and deltas.

“Arsenic gloms onto iron oxide compounds in rocks from the Himalayas. This iron oxide coats surface of sand grains and rock particles. So when the iron-oxide coated sediments are swept down with the river, they mop off arsenic and carry the toxin with them lowland,” said geologist BA Shah of Jadavpur University.

Shah notes the Brahmaputra and adjoining rivers system covering the states of northeastern India has several types of sediment depositions since ages, which serves as reservoirs of arsenic.

“The problem of groundwater arsenic contamination in the entrenched channels and floodplains of the Brahmaputra, Barak and Manipur valleys is similar to the Middle Gangetic Plain (Bihar, Jharkhand and UP) and lower Gangetic Plain of West Bengal and Padma-Meghna-Brahmaputra of Bangladesh,” Shah said.

What makes this naturally occurring form of arsenic harmful is its release into the groundwater in a soluble, toxic form. The release of arsenic stuck on to the iron oxide-coated sediments is associated with the lowering of water table owing to over-exploitation of groundwater for irrigation.

This was set in motion when millions of tubewells were installed in Bangladesh, West Bengal and other regions of the Gangetic plain in India and Nepal, since 1970s, said the International Agency for Research on Cancer, to prevent gastrointestinal diseases linked to surface water consumption.

As people became more dependent on groundwater for irrigation and drinking, it led to overuse of the resource, which in turn, led to an elevated arsenic content in groundwater.

“The withdrawal rates exceed the recharge rates and that leads to overuse. This alters the chemistry of the aquifers and triggers microbial action. Some soil microbes in this (reduced or oxygen-starved) condition use iron oxide for respiration and during this, arsenic attached to iron oxide is split and leached into water flowing through the ground,” Shah explains.

Compounding the water contamination issue is that in many tubewells, iron is high and a connection exists between arsenic and iron.

“If arsenic is present then you can be 100 percent sure iron is also present. But in many cases, arsenic may not be present even when iron is high,” he said.

An abandoned tubewell. Photo by Bishwarup Ganguly/Wikimedia Commons

Troubled waters

About 239 million people across 153 districts in 21 states drink water that contains high levels of arsenic.

Assam lies next-door to the Indian state of West Bengal-one of the worst arsenic-hit states in the country. It also shares the same pattern of distribution and movement of groundwater as Bangladesh, its international neighbour ravaged by the arsenic issue.

According to the latest data supplied by Ministry of Drinking Water and Sanitation in Parliament, over 4500 habitations are arsenic-affected, while close to 6000 have unacceptable levels of iron.

The Assam Public Health Engineering department, found arsenic contamination in water samples from 10,301 sources out of 3,25, 079 in the state last year.

For the Indian government’s Bureau of Indian Standards the acceptable limit for arsenic, beyond which water becomes toxic, is pegged at 10 ppb, whereas 50 ppb is the permissible limit in the “absence of an alternate source”. This is five times higher than the cap (10 ppb) set by World Health Organisation (WHO) at 50 ppb.

“Survey studies are still not sufficient and proper mapping needs to be done (after the number of districts increased to 33) to gauge the extent of the spread,” Nath admits.

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