Rice University scientists are building a new treatment system that can selectively pull toxins from drinking water, sewage systems, and oil wells.
The researchers led by scientist and co-author of a study, professor Qilin Li, are confident that their technology will cut costs and save energy compared to conventional systems.
“Traditional methods to remove everything, such as reverse osmosis, are expensive and energy intensive,” said Li. “If we figure out a way to just fish out these minor components, we can save a lot of energy.”
The basis of the new system is a set of novel composite electrodes that enable capacitive deionization. The charged, porous electrodes selectively pull target ions from fluids passing through the maze-like system.
According to the researchers, when the pores get filled with toxins, the electrodes can be cleaned, restored to their original capacity and reused.
“This is part of a broad scope of research to figure out ways to selectively remove ionic contaminants,” said Li. “There are a lot of ions in water. Not everything is toxic. For example, sodium chloride (salt) is perfectly benign. We don’t have to remove it unless the concentration gets too high.”
“For many applications, we can leave non-hazardous ions behind, but there are certain ions that we need to remove,” Li said. “For example, in some drinking water wells, there’s arsenic. In our drinking water pipes, there could be lead or copper. And in industrial applications, there are calcium and sulfate ions that form scale, a buildup of mineral deposits that foul and clog pipes.”
The system’s electrodes were coated with activated carbon, which was in turn coated by a thin film of tiny resin particles held together by quaternized polyvinyl alcohol.
When sulfate-contaminated water flowed through a channel between the charged electrodes, sulfate ions were attracted by the electrodes, passed through the resin coating and stuck to the carbon.
Tests in the Rice lab showed the positively charged coating on the cathode preferentially captured sulfate ions over salt at a ratio of more than 20 to 1. Moreover, the electrodes were able to retain their properties even over 50 cycles.
Image credits and content: Jeff Fitlow/Rice University