21 November 2013

A Possible Solution for Treating Arsenic in Groundwater

In many places in the world, surface water is either contaminated to the point of being undrinkable or exists in a quantity that is potable but scarce. A popular solution is to instead extract groundwater from deep underground. The issue with this is that despite being cleaner, oftentimes this groundwater will be contaminated with heavy metals such as arsenic due to its contact with the surrounding soil.

AguaClara’s research in arsenic treatment first began in the form of a capstone idea presented in a previous semester of our CEE 4540 course, “Small-Scale Sustainable Water Supplies.” The goal was to direct AguaClara’s research efforts to address the problem of widespread arsenic poisoning in communities around the world that rely on contaminated groundwater as their primary water source. A team of students was formed the following semester to research possible solutions to this large-scale problem.

This semester, the Arsenic Team has begun testing methods for separating arsenic from water in order to render the water potable. One of the team’s goals is to see if their idea of using AguaClara’s process of water treatment as a base could, with some adjustments, work similarly effectively for arsenic.

Flocculation, as it works in the AguaClara plant, entails dosing pre-treated water with a coagulant so that unwanted particles will stick to one another to form larger masses called flocs. As they become heavier than the water, these flocs are pulled to the bottom of our tank by gravity through a process called sedimentation. The water is then filtered.

In modifying this process for arsenic removal testing, the team will first dose a sample of mock groundwater with known concentrations of arsenic and coagulant. The samples with then be mixed at a low speed in a tumbler to simulate flocculation. After flocs form, the container with the sample will then be placed into a centrifuge and rotated at a high enough velocity that the flocs—hopefully containing the arsenic—will be distinctly separated from uncontaminated water. The sample will then be analyzed using a spectrometer to measure the remaining concentration of arsenic in the sample.

From left: Imtiaz, Tanapong, and Michelle preparing a sample for the spectrometer.
Most recently, the team has been testing to see if a combination of filtration and sedimentation by centrifuge­—with varying coagulant dosage—will aid in the removal of arsenic from mock groundwater.

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