A rubber-like polymer gel layer can minimise leakage of polluted water from waste disposal sites, says Mohamed Darwish. The elastic and self-healing gel can trap toxic ions.
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Nothing in this world is completely impermeable. But a gel developed in Dietz Laboratory, by TU PhD student Mohamed Darwish and his supervisor Dr. Pacelli Zitha, comes close. This polymer gel can protect the environment around landfill sites from the rainfall that washes ions or toxic waste out of waste disposal sites.
Darwish’s calculations and experiments in the laboratory reveal that the polymer gel efficiently retards a flux of anions and cations, which occurs at waste disposal sites. Darwish subsequently came up with the idea of using the gel % originally developed to block water flow in older oil wells % as a protective layer beneath landfills.
In Western countries, clay layers sandwiched with plastic or geotextiles currently prevent toxic waste from leaking into the environment. However, during construction or waste dumping, these thin, delicate layers are sometimes damaged by negligent truck and bulldozer drivers, or by sharp objects in the rubbish. Moreover, clay may crack due to the adsorption of some ions, or by drying out. “A big part of the layer already malfunctions when there is only one hole in it,” says Darwish, a civil engineer from Egypt, who is working on his PhD at TU Delft’s Dietz-Laboratory.
Without large holes, existing clay layers hardly let any water through. Ions, however, can find their way through clay layers. “Because clay layers are negatively charged by nature, negative ions don’t stick to the clay particles. The clay particles don’t retard them and that’s why they can go through the pores quickly,” Darwish explains. And when lots of negatively charged ions pass through the clay layer, the positively charged ions want to join them, attracted by the small, negatively charged ions that come into being beneath the clay layer.
Jelly pudding
This phenomenon doesn’t occur in the gel layer, because gel can both be positively and negatively charged. It’s possible to mix these gel layers with sand and thereby trap both negative and positive ions. Moreover, the pores of the gel are much smaller than those for clay. Darwish’s experiments with magnetic resonance imaging, a technique used in hospitals for scanning, revealed that – depending on the concentrations of ions – the ions only partly penetrated the gel. By making the gel thick enough, it’s possible to completely block the ions.
Furthermore, the gel is elastic and self-healing. “It’s like when you put a spoon in a jelly pudding and then remove it, the jelly closes itself again and water can hardly pass through it.”
Darwish cannot yet reveal the gel’s composition, because he and his supervisor are filing a patent for this application. The polymer and the cross linker were tested and have proven to be safe for human beings and the environment, Darwish confirms.
“The gel can last for years, because the cross linkers bind the separate polymers to each other with strong chemical bonds. The gel is not a good nutrient for micro-organisms. But even if it were, germs can only eat tiny pieces on the gels exterior. And strong chemicals don’t damage the gel either,” Darwish adds. “We’ve shown that by conducting experiments with synthetic leachate.”
Until now, Darwish has only performed lab experiments. “I’d like a company to offer us a site for real-life experiments.”
Valuable
A long lifetime for the protective layer is a necessity. Nowadays, landfills in the Netherlands have afterlives, and landfill operators are aware that their waste pile will someday become a ski slope, for example, or a golf course or nature area. Although the Dutch government promotes alternatives for land filling, in 2000, six million tons of waste was land filled.
Every year about three new landfill sites are opened in The Netherlands, which is not many, but Darwish claims his gel can also be used as a problem-solver at existing sites. If the soil is contaminated, for instance, the gel can be injected into the soil in a circle around the waste disposal site and prevent contaminated water from spreading.
In the Middle East, however, constructing landfills is a growing business, Darwish says. “These countries are running out of water, so groundwater becomes more valuable and something that you’d better not contaminate.” In his native Egypt, waste used to be dumped in the desert: About five years ago we started looking at possibilities for cultivating the desert, and this means you must then preserve the groundwater by minimising its contact withwaste piles.”
A rubber-like polymer gel layer can minimise leakage of polluted water from waste disposal sites, says Mohamed Darwish. The elastic and self-healing gel can trap toxic ions.
Nothing in this world is completely impermeable. But a gel developed in Dietz Laboratory, by TU PhD student Mohamed Darwish and his supervisor Dr. Pacelli Zitha, comes close. This polymer gel can protect the environment around landfill sites from the rainfall that washes ions or toxic waste out of waste disposal sites.
Darwish’s calculations and experiments in the laboratory reveal that the polymer gel efficiently retards a flux of anions and cations, which occurs at waste disposal sites. Darwish subsequently came up with the idea of using the gel % originally developed to block water flow in older oil wells % as a protective layer beneath landfills.
In Western countries, clay layers sandwiched with plastic or geotextiles currently prevent toxic waste from leaking into the environment. However, during construction or waste dumping, these thin, delicate layers are sometimes damaged by negligent truck and bulldozer drivers, or by sharp objects in the rubbish. Moreover, clay may crack due to the adsorption of some ions, or by drying out. “A big part of the layer already malfunctions when there is only one hole in it,” says Darwish, a civil engineer from Egypt, who is working on his PhD at TU Delft’s Dietz-Laboratory.
Without large holes, existing clay layers hardly let any water through. Ions, however, can find their way through clay layers. “Because clay layers are negatively charged by nature, negative ions don’t stick to the clay particles. The clay particles don’t retard them and that’s why they can go through the pores quickly,” Darwish explains. And when lots of negatively charged ions pass through the clay layer, the positively charged ions want to join them, attracted by the small, negatively charged ions that come into being beneath the clay layer.
Jelly pudding
This phenomenon doesn’t occur in the gel layer, because gel can both be positively and negatively charged. It’s possible to mix these gel layers with sand and thereby trap both negative and positive ions. Moreover, the pores of the gel are much smaller than those for clay. Darwish’s experiments with magnetic resonance imaging, a technique used in hospitals for scanning, revealed that – depending on the concentrations of ions – the ions only partly penetrated the gel. By making the gel thick enough, it’s possible to completely block the ions.
Furthermore, the gel is elastic and self-healing. “It’s like when you put a spoon in a jelly pudding and then remove it, the jelly closes itself again and water can hardly pass through it.”
Darwish cannot yet reveal the gel’s composition, because he and his supervisor are filing a patent for this application. The polymer and the cross linker were tested and have proven to be safe for human beings and the environment, Darwish confirms.
“The gel can last for years, because the cross linkers bind the separate polymers to each other with strong chemical bonds. The gel is not a good nutrient for micro-organisms. But even if it were, germs can only eat tiny pieces on the gels exterior. And strong chemicals don’t damage the gel either,” Darwish adds. “We’ve shown that by conducting experiments with synthetic leachate.”
Until now, Darwish has only performed lab experiments. “I’d like a company to offer us a site for real-life experiments.”
Valuable
A long lifetime for the protective layer is a necessity. Nowadays, landfills in the Netherlands have afterlives, and landfill operators are aware that their waste pile will someday become a ski slope, for example, or a golf course or nature area. Although the Dutch government promotes alternatives for land filling, in 2000, six million tons of waste was land filled.
Every year about three new landfill sites are opened in The Netherlands, which is not many, but Darwish claims his gel can also be used as a problem-solver at existing sites. If the soil is contaminated, for instance, the gel can be injected into the soil in a circle around the waste disposal site and prevent contaminated water from spreading.
In the Middle East, however, constructing landfills is a growing business, Darwish says. “These countries are running out of water, so groundwater becomes more valuable and something that you’d better not contaminate.” In his native Egypt, waste used to be dumped in the desert: About five years ago we started looking at possibilities for cultivating the desert, and this means you must then preserve the groundwater by minimising its contact withwaste piles.”
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