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Nanofiltration could solve US water crisis

Research undertaken by the UH Cullen College of Engineering could help improve surface and groundwater supplies in the US by improving nanofiltration methods for eliminating contaminants.

Work carried out by Shankar Chellam, professor of civil and environmental engineering at the college, has improved the methods for eliminating contaminants such as bacteria, viruses, organic matter and inorganic chemicals from surface waters that serve as municipal water supplies, and the goal is to also remove salt from the mix.

In Oklahoma, 65% of topsoil and 74% of subsoil are short or very short of moisture, and 20% of pastures and rangelands are rated poor or very poor, according to the Drought Monitor. Texas fares slightly better with 53% of topsoil and 61% of subsoil short or very short of moisture. However, the Lone Star State’s pastures and rangelands are worse off with 31% rated poor to very poor.

The drought worsens existing water quality issues that include new pollutants, increasing pollutant concentrations, growing population pressures and over-utilization of groundwater, which are taking tolls on water supplies around the world. Consequently, the relatively clean surface water and groundwater supplies that were available 50 years ago are essentially nonexistent today.

Nano versus RO

Nanofiltration membranes, which are less expensive than reverse osmosis (RO) membranes, can potentially fill a niche for waters that fall somewhere on the salt spectrum between relatively unsalted lakes, such as Lake Conroe, and briny oceans. Nanofiltration might require about 70 pounds of pressure per square inch to push lake water through membranes that remove salt, while RO could require more than three times that amount of pressure to squeeze ocean water through membranes that desalinate.

“We want to implement less expensive processes so the induction into an actual technology can happen faster,” said Chellam.

Aspects of the research include understanding the mechanisms by which contaminants pass through filters to determine ways to improve their removal, optimizing flow of water without irreversibly clogging filters and determining ways to clean or regenerate filters when they clog, which is inevitable.

To prolong the lives of filters, Chellam plans to evaluate electroflotation, a novel pretreatment to prevent clogging. Polymer nanofiltration membranes have irregular-shaped, nano-sized pores that filter salt and contaminates by size exclusion and charge repulsion. The filters mimic most natural systems with negative charges that repel negatively charged contaminants.

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