Column Studies on Arsenic Removal from Ground Water for Filter Development in Rural Areas

Groundwater is a vital source of drinking water in rural India, but its quality is severely compromised in many areas due to naturally occurring arsenic. Prolonged exposure to arsenic-contaminated water can lead to severe health issues such as skin lesions, internal cancers, and cardiovascular diseases. The World Health Organization (WHO) and the Bureau of Indian Standards (BIS) prescribe a maximum permissible limit of 0.01 mg/L for arsenic in drinking water, but in many rural areas, arsenic levels far exceed this guideline. Traditional treatment technologies are often economically and operationally unfeasible in rural settings. Despite awareness and ongoing remediation efforts, the challenge remains largely unresolved in rural areas due to the lack of affordable, accessible, and low-maintenance water purification technologies. Most commercially available arsenic-removal systems are cost-prohibitive, require electricity or skilled operation, or involve maintenance complexities that are unsuitable for rural settings. The ultimate goal of this work is to contribute toward the development of a cost-effective, sustainable, and user-friendly household filtration system that rural communities can easily adopt using locally sourced materials—thereby enhancing access to safe drinking water and protecting public health.

LITERATURE REVIEW

Bretzler (2020) conducted an extensive investigation into zero-valent iron (ZVI) filters in Burkina Faso showed arsenic removal efficiencies ranging from 60% to 80% in field conditions and 95% under optimized settings.

Diprupa Bhaktiari (2018) from Assam has developed a simple and low-cost filter for both arsenic and iron removal using process based on oxidation-coagulation-adsorption by three common chemicals (baking soda, potassium permanganate, ferric chloride) having around 99% removal efficiency.

Abedin (2011) investigated the application of mixture of ZVI and sand to remediate the arsenic in contaminated water in a laboratory setup. The flow rate maintained for 180 days. It showed removal of 99% arsenic.

Mwakabona (2017) Usage of low-cost filters with nails as the active ZVI layer tested in field and laboratory. Fe-hydroxides to stable magnetite with incorporated As(V) achieving 60–80% As removal in fields and in lab columns >95%.

Ngai (2007) developed household water filters known as the Kanchan arsenic filter (KAF). These filters can remove 85-90% of arsenic from drinking water. The components used in these filters were sand, gravel, iron nails, brick chips and bio sand layer where iron nails can remove approximately 85–90%

Lackovic (2000) examined the use of zero-valent iron (ZVI) for the removal of inorganic arsenic from water. ZVI can reduce arsenic (III) to arsenic (V) through electron transfer. This is significant because arsenic (V) is less toxic and more readily adsorbed onto iron oxides. ZVI can achieve high arsenic removal efficiencies, often in the range of 85-99%.

OBJECTIVE:

Study and finding of arsenic content in parts of Assam and design of column tests using various filter media heights for the removal of arsenic in water and design recommendation of a low-cost filtration system based on experimental results.

METHODOLOGY:

Study Area and Sample Collection:

According to an assessment published by Assam’s Public Health Engineering Department in 2023, 6881 habitations in the state are affected by arsenic across 20 districts. Baksa district in lower Assam had highest 1506 such affected habitations. In upper Assam’s Jorhat district, 1454 habitations were affected followed by 1342 in Nalbari district. For this study, we had chosen and gathered water samples from seven pin points of Jorhat and Golaghat districts to find out the probable arsenic content.

Laboratory tests: Samples are tested in the loaboratory of Public health Engineering Department Jorhat by standard methods for parameters such as arsenic, iron, pH, alkalinity, hardness, turbidity, conductivity, nitrate, chloride, calcium, magnesium, fluoride.

Materials Used: The following materials were selected based on local availability and prior arsenic removal research:

Iron nails: Iron oxide removes arsenic from water through a process known as adsorption, where arsenic ions bind to the surface of iron oxide particles. The arsenic ions either stick to the surface or may be incorporated into solid phases, like iron arsenate (FeAsO₄), which further reduces the arsenic's mobility in the water.

Sand: Sand may be used as a secondary or polishing layer in filters to remove any remaining fine particles or turbidity from the water after it has passed through the main arsenic-removal media and helps regulate the flow rate of water through the filter. Sand can be cleaned and reused through processes like backwashing, making it a sustainable choice for filtration.

Gravel and brick chips: Gravel serves multiple purposes, including supporting the finer filtration media, enhancing water distribution, and preventing clogging. It also aids in efficient drainage and backwashing, which helps maintain the filter's performance and longevity.  brick chips play an important role in improving the filter's structure, ensuring optimal water flow, providing pre-filtration, and enhancing contact with arsenic-removal media

Bamboo charcoal: It serves as an eco-friendly and natural water purifier, harnessing its porous structure to effectively adsorb impurities and contaminants present in water. Its high surface area and absorptive qualities make it a compelling choice for water purification.

Column Design: Column tests are crucial before conducting real field tests or designing a filter system because they provide a controlled, laboratory-scale environment to simulate real-world water treatment conditions. These tests allow for the evaluation of various filter materials, bed heights, and flow rates to determine the most effective combination for removing specific contaminants, such as arsenic or iron. Column Length 500 mm, Diameter 30mm, Material glass. Various column experiments are done using different bed height for each material and find out how it effect in removal of arsenic and other contaminants from water.

Untreated Sample Test Result

Table 1

Table 2:  Different bed height combinations for Arsenic Removal