Chemistry Environment Health and Medicine

Tap Water Purification Through Tracking Aluminum

tap water purification

Scientists from Kobe University have created a new analysis method that uses magnetic fields in order to quickly and accurately measure the concentration of aluminum used to purify tap water. These latest discoveries hold the potential to be used in developing efficient and environmentally-conscious coagulants for water treatment. 

Providing clear, safe tap water requires particles known as colloids to be removed from raw water. These particles are extremely small (between nanometer order and micrometer order in diameter). Polychlorinated aluminum is used as a coagulant in the water treatment process in order to collect and get rid of these particular particles. Aluminum ions unfortunately have been known to be very toxic to fish and can even inhibit the growth of some plants. The Japanese Water Works Law states that aluminum concentration within any body of water much remain below 0.1 ppm (or 1:10,000,000) in order to be considered a safe amount.

A number of hydrolyzed species of aluminum ion can be detected within water. Until now, only the “ferron method” has been widely used in order to calculate the concentration of these compounds. This method involves pigments and absorption meters.

water purification
Analysis that is using 27Al qNMR (quantitative NMR) spectroscopy. Each seperate spectrum can be measured in just 3 minutes. (Image credit: Kobe University)

Associate Professor Maki’s research group optimized NMR¹ equipment in order to develop an analysis method known as Al qNMR (or quantitative NMR) spectroscopy that is able to accurately measure the amount of aluminum compound. Measurements using this analysis method can be completed within a matter of three minutes. The concentration of hydrolyzed species can be calculated within a very small margin of error in all pH ranges.

Following analyzing the agglomeration mechanism of sludge including the aluminum ion, the group realized that when there is a large concentration of aluminum ions, about 100 minutes later, a Keggin-type tridecameric cluster (also known as K-Al13) is formed and within a few months polymerization happens.

The new analysis method makes it much easier to measure the concentration of aluminum ions in water and is also able to clarify the structural changes aluminum ions undergo over a period of time. These new discoveries could contribute to the development of a high performance, environmentally-conscious coagulant that can act more efficiently on colloids.

This method analyses molecular compounds at the atomic level by putting nuclei in a magnetic field and recording their resonance frequency. Most analysis currently in practice are required to use dipolar nuclei involving carbons and protons but this new method simply uses the quadrupolar nuclei of aluminum. This is the world’s first ever reported example of a fixed-quantity NMR spectroscopy on quadrupolar nuclei.

The complete findings were presented on May 29th, 2016 at the 76th Japan Society for Analytical Chemistry Symposium.