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Clean wastewater treatment filters without damaging them

Membrane filters do not require a lot of energy to purify water, which makes them popular for wastewater treatment. To keep these materials in pristine condition, they are usually cleaned with copious amounts of strong chemicals, but some of these agents destroy the membranes in the process. Now, researchers at ACS Applied Materials & Interfaces have developed reusable nanoparticle catalysts that incorporate glucose to help efficiently break down contaminants inside these filters without damaging them.

Typically, dirty sewage filters are not clogged with strong acids, bases, or oxidizers. Chlorine-containing oxidizers such as bleach can break down the toughest organic debris. But they also damage polyamide membranes, present in most commercial nanofiltration systems, and they produce toxic byproducts. A milder alternative to bleach is hydrogen peroxide, but it slowly breaks down contaminants. Previously, scientists have combined hydrogen peroxide with iron oxide to form hydroxyl radicals that enhance the effectiveness of hydrogen peroxide in a process known as the Fenton reaction. Yet, for the Fenton reaction to clean the filters, additional hydrogen peroxide and acid are required, increasing financial and environmental costs. One way to avoid these additional chemicals is to use the enzyme glucose oxidase, which simultaneously forms hydrogen peroxide and gluconic acid from glucose and oxygen. So Jianquan Luo and his colleagues wanted to combine glucose oxidase and iron oxide nanoparticles into a system that catalyzes the breakdown of Fenton-based contaminants, creating an efficient and delicate cleaning system for membrane filters.

First, researchers compared the removal of organic contaminants from polyamide filters by the enzyme glucose oxidase and iron oxide nanoparticles to other cleaning methods, including the traditional Fenton reaction. They found that this approach was superior at breaking down common contaminants bisphenol A and methylene blue, while further preserving membrane structure. Encouraged by their early results, the team combined glucose oxidase and iron oxide into a single nanoparticle, linking them through an amino bridge. Finally, they tested the new nanoparticle’s ability to clean methylene blue-soaked nanofiltration membranes, which they fouled and cleaned for three cycles. After each cleaning cycle, the nanoparticles were picked up with a magnet and reused with fresh glucose to activate the catalyst. The nanoparticles were very effective in cleaning the membranes, bringing them back to 94% of their initial water filtration capacity. Because the nanoparticles don’t require harsh chemicals and are easily scavenged, the researchers say their new system is a “greener” and more cost-effective approach to cleaning nanofiltration membranes.

Reference: Zhang J, Zhang H, Wan Y, Luo J. Chemoenzymatic cascade reaction for green cleaning of polyamide nanofiltration membrane. ACS Application Interfaces. Published online March 2, 2022. doi:10.1021/acsami.1c23466

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