From waste plastic to wastewater treatment

Appropriating waste PET bottles may help to remove antibiotics from wastewater.

A research team from the Korea Institute of Science and Technology (KIST) Water Cycle Research Center has developed a high-efficiency, adsorbent material using PET waste bottles. The new material is expected to help solve the problem of environmental toxins and antibiotic-resistant bacteria caused by leaks of antibiotics into water.

Due to high rates of antibiotic use, South Korea is categorised as a country at high risk of the emergence of multidrug-resistant bacteria, or so-called ‘super bacteria’. According to the Ministry of Environment, antibiotic substances have been detected at livestock wastewater treatment facilities, at sewage treatment plants and in rivers.

Currently, the most well-known method of effectively removing antibiotics from water uses porous carbon composite, synthesised by pyrolysing metal–organic frameworks (MOF). Porous carbon composites adsorb antibiotics in the water, thereby removing them. However, since the organic ligand generally used to synthesise MOF is very expensive, the cost is a major obstacle to this method’s widespread, practical application through mass production.

Looking to develop a more cost-effective solution, the KIST research team — led by Jung Kyung-won and Choi Jae-woo — turned to the PET bottles that people use in their everyday lives.

PET is a high-molecular compound obtained by polymerising ethylene glycol and terephthalic acid, the latter of which is used as organic ligand for the syntheses of MOF. The KIST research team extracted high-purity organic ligand from PET waste bottles and used it to synthesise a high-efficiency adsorbent material that could effectively remove antibiotics from water in an environmentally and economically beneficial way.

During the development of this adsorbent material, an alkaline hydrolysis process was used to induce a neutralisation reaction, resulting in the production of a high-purity terephthalic acid. To maximise the efficiency of the alkaline hydrolysis process, the research team incorporated an ultrasound-assisted phase transfer catalyst process. By optimising this process, the team was able to extract 100% high-purity terephthalic acid, which was used to develop a porous carbon composite.

Iron-based MOF was used as a precursor in order to impart magnetism to the adsorbent material. In this way, the team was able to develop an eco-material that can be easily separated from the mixture after the adsorption process, using an external magnetic field.

The KIST research team tested the efficiency of the porous carbon composite in terms of its ability to adsorb tetracycline — the antibiotic used to treat bacterial infections — from the water. Tests showed that the newly developed material was able to remove 100% of the tetracycline in about 90 minutes under general water conditions (pH 6), with an adsorption rate of 671.14 mg/g, which is a rate superior to that of previously developed adsorbents.

To assess the re-usability of the porous carbon composite, the adsorption–desorption process was conducted five times. Even after repeated use, the material maintained 90% of its adsorption properties, indicating a high degree of stability and wide applicability for water treatment.

“This porous carbon composite is applicable to a wide range of water treatment areas as it uses waste plastics to prevent environmental pollution and maintains its high adsorption properties even after repeated use,” Dr Jung Kyung-won said.

Dr Choi Jae-woo added, “The porous carbon composite developed through this research is applicable to various fields, ranging from eco-materials to energy materials, and I expect that it will soon be highly regarded as a value-added eco-material.”

Image caption: The KIST research team extracted high-purity organic ligand from PET waste bottles and used it to synthesise a high-efficiency adsorbent material that could effectively remove antibiotics from water in an environmentally and economically beneficial way. During the development of this adsorbent material, an alkaline hydrolysis process was used to induce a neutralisation reaction, resulting in the production of a high-purity terephthalic acid. Image credit: Korea Institute of Science and Technology (KIST).