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Comment Water Treatment

Low-cost water treatment uses CO2 to remove particles without membranes

By Chemical Engineering |

Researchers at Princeton University (Princeton, N.J.; www.princeton.edu) have developed a water treatment technique that injects carbon dioxide gas into a stream of water to separate suspended particles that would be difficult to remove by sedimentation or by microbes. The system, built initially at laboratory-scale, removes suspended particles 1,000 times more efficiently than conventional filtration units, and does not require membranes, the research team says. The low-cost, low-energy system could be used as a replacement to microfiltration and ultrafiltration, or as an adjunct to conventional filtration, protecting membranes from fouling. The system could also be used to separate waterborne bacteria and viruses without chlorination or treatment with ultraviolet light, the researchers say. The system works by taking advantage of a principle called diffusiophoresis, whereby the movement of solid particles in water is induced by an ion concentration gradient. The ion gradient is set up by dissolving CO2 gas in water, forming carbonic acid. The acid dissociates into hydrogen ions and HCO3– ions, similar to the chemistry that occurs in carbonated beverages. Large differences in the diffusivities of H+ and HCO3– ions create a diffusion…
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