New Micropollutant Removal Method Traps and Neutralises Contaminants

When contaminants such as pharmaceuticals and other harmful compounds are present in low concentrations, they often slip through wastewater treatment processes whilst remaining a threat to the flora and fauna found in rivers and streams.

Indeed, even the most miniscule concentrations of harmful compounds such as flame retardants or antibiotics can be potentially life-threatening to the fish and plant life living in the affected water.

In order to address the problem, a Chinese scientist at the Dalian University of Technology Xiyun Cai has developed a new technique of capturing these dangerous compounds and destroying them before they even leave the treatment plant.

Inadequate Existing Methods

Back in 2010, water treatment company ITT announced the launch of a revolutionary new Advanced Oxidation Process (AOP) solution which at the time was the most advanced method of neutralising harmful compounds in wastewater. The solution was the first to combine the three different methods of ozone (O3), ultraviolet light (UV) and hydrogen peroxide (H2O2), thus making it an attractive proposition.

While generally effective, this technique is less than ideal since it can lead to the creation of many harmful by-products, such as formaldehyde.

One other method is the use of powdered activated carbon to adsorb the micropollutants, which is then separated from the rest of the liquid and disposed of by combustion. However, this method is also far from perfect, since much natural organic matter can also become adsorbed by the carbon, thus wasting much expensive carbon powder in the process. As such, it’s not a very cost-effective solution to the problem.

A One-Two Knockout Punch

 Xiyun Cai and his team attempted to overcome these problems by approaching the issue from a different angle. Instead of oxidation, they designed unique insoluble polymers which are composed of cyclodextrins combined with epichlorohydrin. The cyclodextrins are derived from starch and are more selective in their isolation of micropollutants, since the hydrophobic cavity does not capture the natural organic matter which made previous methods financially unfeasible and inefficient.

Then, the team used KMnO₄, a commonly-found compound which neutralises the harmful micropollutants into degraded constituents such as water, carbon dioxide (CO²) and organic acids.

The method was tested both on the flame retardant tetrabromobisphenol A (TBBPA) and on a number of different antiobiotics, all at concentrations representative of the levels they are commonly found in wastewater. After applying the process outlined above to the samples, they found that the cyclodextrin had adsorbed 94% of TBBPA and anywhere between 12% and 79% of the antiobiotics within four hours of the process. Similar results were discovered when the process was applied to water containing organic matter, calcium and magnesium, which proved these would not interfere with the efficacy of the technique.

Although the efficiency of the cyclodextrin was not as high as hoped for some of the antibiotics, it does have a similar level of success as existing methods and comes with a number of advantages. Firstly, the process could be applied to any number of different pollutants, including pharmaceuticals, pesticides and cosmetics. Secondly, it does not come with harmful by-products. And finally, the cyclodextrins and the KMnO₄ are cheap to manufacture and the former can even be reused.