When fat, oil and grease (FOG) materials hit sewers, they tend to go through hydrolysis and saponification reactions during which they amalgamate with other debris flushed down the toilet.
The whole horrible mess adheres to the inner sewer surface, and so a fatberg is born. Metals, particularly calcium, that leach from the predominantly concrete pipes exacerbate the problem and promote further adhesion.
Ironically, it is now known that traditional pipe protective coatings, such as magnesium hydroxide add to the problem by interacting with fatty acids, causing them to coagulate.
Some fatbergs are monstrous: London had to deal with a 250-m-long, 130-ton specimen in 2017. In 2021, a 330-ton version in the U.K.’s second-largest city, Birmingham, was estimated to be one meter thick and 1,000 meters long.
Earlier this year, Thames Water removed a 35-ton berg from an East London sewer. Largely made up of unflushable items such as tampons, wet wipes and condoms, plus silt, it took 20 workers 11 days to clear it. The company estimates that it has spent at least £90 million ($125 million) removing wet wipes from its sewers over the last five years.
Melbourne, Australia; Baltimore; Singapore; and Dannevirke, New Zealand, also have suffered berg-related issues.
The U.K. spends over £100 million a year ($95 million annually) dealing with its FOG-related challenges, according to an article in Science of The Total Environment. Australia spends A$100 million a year ($65 million a year) and the United States a whopping $25 billion annually tackling their fatberg problems, the article states.
HOFs Show Promise in Pipe Protection
However, help is at hand following a new protective coating developed by engineers at RMIT University in Melbourne, Australia. The coating reduces 80% of the calcium that can leach into concrete sewer pipes.
To do this, they turned to a class of materials known as hydrogen-bonded organic frameworks (HOFs), porous materials formed from organic linkers that self-assemble through hydrogen bonding.
Unlike the better-known metal-organic frameworks, HOFs do not leach metal ions and so are well suited to fend off fatberg formation.
Their highly stable LH4-HOF has high surface area and crystallinity and forms a porous 2-D structure via hydrogen bonding. When mixed with an epoxy resin and cured at 60°C, the resulting material is a self-healing polyurethane sheath.
Study lead Biplob Pramanik mimicked a sewer environment under extreme conditions that rapidly sped up the fatberg formation process over 30 days (Figure 1).
“It showed the coating reduced build-up of FOG on concrete by 30% compared to non-coated concrete,” said Pramanik, director of the Water: Effective Technologies and Tools Research Centre at RMIT. “This reduction can be attributed to the significantly reduced release of calcium from coated concrete, as well as less sticking of FOG on the coating surface compared to the rough, uncoated concrete surface.”
Traditional coatings like magnesium hydroxide can control sewer corrosion but can inadvertently contribute to FOG build-up by interacting with fatty acids, Pramanik noted.
The RMIT-developed coating is stable in water and withstands temperatures of up to 850°C, according to the researchers. Its self-healing properties mean that the coating’s lifespan can also be extended.
Although HOFs possess many novel and advantageous properties, their aggregation behavior remains poorly understood. So, uncovering the mechanisms of HOF-based coating formation, optimizing solution processing methods and developing novel fabrication technologies will be part of the RMIT team’s ongoing work.
The engineers also are working to improve their existing coating by making it even less susceptible to FOG deposition while enhancing both its self-healing properties and mechanical strength. Such adaptations, they note, will be of use in industrial settings where surface protection, chemical resistance and long-term durability are required.
Pramanik is the chief investigator for a recently announced, government-funded project to develop an advanced grease interceptor for restaurants and other food-service establishments to remove small FOG particles more effectively than current technologies.
