A wide range of research and development is being conducted to solve the challenges of providing clean water, with a significant emphasis on drinking water. The research focus has included advanced membrane technology; changing water chemistry to suit the remediation technology of choice; and media modification for increased selectivity, activity and capacity.
The purpose of this study is to focus on sorptive media modification for improved performance.
With many areas, especially in developing countries, seriously limited by the quantity or quality of drinking water, there is an urgency both to develop new technologies and advance existing technologies. This has heightened the need to promote the long-term availability and quality of water resources. Fortunately, overcoming the limitations associated with the traditional water treatment methods of filtration and chemical treatment has progressed substantially in recent years, in part because of treatment media advancements through application of nano-science. Nano-science changes the media morphology, greatly increasing media surface area and thereby increasing both activity and capacity in contaminant sorption.
Prominently discussed in industry and academic forums for years, the tangible benefits of nanotechnology-based methods for treating drinking water are gaining recognition in the water treatment industry. In particular, the advancement of nano-particles for use in the adsorption of inorganic contaminants (lead and arsenic) is demonstrating superior performance compared to traditional adsorbent technologies. Nano-particles are measured in nanometers (nm), or billionths of a meter, and are typically defined as particles with a size ranging from 1 to 100 nm. Relative to traditional micro-sized particles, nano-scale materials are predominantly more chemically reactive, maintaining a substantially higher surface area and enhanced surface characteristics. For drinking water treatment applications, this provides the quantified benefits of increased affinity, capacity and selectivity for heavy metals and other contaminants. Even when aggregated into larger diameter colloids, the enhanced chemical and physical characteristics of the primary nano-particle is evident. Nano-adsorbents are being incorporated into an array of commercially available filtration systems to improve contaminant removal efficiency and extend operating life. Specifically, colloids of proprietary nano-titanium compounds are demonstrating advanced heavy metal adsorption characteristics.
Titanium compounds are truly multifunctional. The well-known photocatalytic properties of titanium have been recognized as effective for the destruction of bacteria and other organics in water. The catalytic properties have been used in air purification to remove nitrogen oxide. More recently, the adsorption advantages of proprietary titanium compounds are being applied for the removal of lead, arsenic, uranium and other heavy metals in drinking water treatment with industry leading results.
This study compares the soluble lead removal characteristics of a proprietary, commercially available nano-structured titanium compound compared to an industry recognized micro-sized silicate adsorbent for soluble lead removal.
Experimental Method & Results
In an effort to compare the capacity and kinetics of an aggregate of nano-particles of a proprietary titanium compound to an industry recognized micro-silicate, an equal quantity of both (1 g) were added to individual 1,000-mL beakers of challenge water. The challenge water was designed to closely replicate the NSF Standard 53 test water for background contaminants; however, a lead concentration of 50 mg/L (parts per million) was chosen to enhance the analytical resolution.
The individual adsorbents were added to the challenge water with stirring to ensure intimate contact with the test solution. Samples were retrieved at timed intervals of 30 seconds through the testing period. The samples were analyzed for lead utilizing an ICP instrument (U.S. EPA Method 200.5) and recorded. At the conclusion of the testing period the results were tabulated for interpretation.
The results of the lead adsorption evaluation confirm the kinetics of the nano-titanium compound exceed that of the micro-sized silicate product. The increased surface area and enhanced selectivity associated with the nano-structure are most likely contributing to the kinetic performance. Separate, as yet unpublished, capacity evaluations of the proprietary nano-titanium compound have confirmed equilibrium capacity values exceeding traditional adsorbents by nearly two times. These performance enhancements can provide improved heavy metal removal efficiencies per mass of adsorbent, resulting in improved filtration product performance and extended product operating life cycles. wqp