Membrane filters out antibiotic-resistant bacteria in wastewater

A TECHNIQUE has been developed combining a photocatalytic membrane and UV light to remove most antibiotic-resistant bacteria and genes from wastewater.

The widespread use of antibiotics has created antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs), which are fragments of DNA from broken cells. These can build up in the environment, including soil, drinking water, and wastewater treatment facilities. Most wastewater facilities are not designed to remove ARB and ARGs. Instead, they can become breeding grounds for bacteria which can evolve into hardier strains, and if the genes encounter living bacteria they can pass the antibiotic resistance onto the bacteria.

Membranes can be used to remove ARBs and ARGs, but suffer from fouling as small bits of DNA clog up the membrane leading to the buildup of bacterial and genetical material that deteriorates the membrane performance. UV disinfection is effective at destroying bacteria, but it is challenging and inefficient to use it continuously.

Researchers in China and the US have developed a membrane that can remove the antibiotic resistant genes and bacteria when exposed to UV. They coated a commercially-available polyvinylidene fluoride membrane with dopamine to polymerise the surface of the membrane. The membrane was then immersed in a solution of titanium dioxide nanoparticles. When illuminated with UV, the TiO₂ nanoparticles act as a photocatalyst to create reactive oxygen species that can kill bacteria.

The team tested their membrane on wastewater effluent from a treatment plant in Jinan City, China. The membrane captured 99.9% of bacteria and deactivated over 90% of the ARGs, although for one particular group of genes only 58% were captured and 20% degraded. Different reactive oxygen species can inactivate specific genes, although the process is still not completely understood.

They also tested the antifouling capabilities by allowing the membrane to get clogged and then exposing it to UV, which restored normal water flow. The photocatalytic membrane prevents fouling by effectively inactivating the ARB and ARGs.

Further testing will need to be done to ensure that the membranes are viable long term, as membranes in treatment plants typically need to function for several years.

Environmental Science & Technology http://doi.org/cs2r