Nanoparticles for Water Treatment in Mexico

Dr. Vicki Colvin
Dr. Pedro Alvarez
Dr. Mason Tomson
Dr. Michael Wong
Dr. Qilin Li

In too many countries children and adults alike risk deadly diseases and chronic illness every time they drink a cup of water.  Improvements in public health for these and other developing nations require improved access to clean water for urban and rural areas alike.  Technological solutions for this problem in developing nations are unlikely to resemble those in place in our own country where municipal water treatment systems and effective distribution systems are the rule.  Innovation is essential to recreate small-scale treatment plants, as well as community point-of-use technologies, that are cheap, reliable and safe for diverse water conditions and settings.  Nanotechnology and the diverse materials and systems it enables hold great potential for meeting this particular global challenge.  Rice University with its leadership in nanotechnology, water purification, and sustainable development is perfectly positioned to contribute to sustainability in this arena.

The state of Guanajuato, and in particular its capital city Guanajuato, provides for Rice an ideal location for water treatment testbeds based on nanotechnology-enabled systems.  This city has the resources to improve its water, the know-how to build facilities, and an appetite for adopting the latest state-of-the-art technology.

Rice University now has in place a Memorandum of Understanding with the City of Guanajuato.  The Project Manager Coordinator in Guanajuato is Dr. Jorge V. Duran.  In addition to Dr. Duran, our researchers work closely with SIMAPAG (Guanajuato's Water Authority), SIMAPAG's Director Rafael Zarate Araizaz, the elected City Mayor Mr. Niseforo Guerrero, and Senator Francisco Arroyo Vieira.

About Guanajuato’s Water

Guanajuato is a city of 180,000 people located in central Mexico, in a region known for its rich deposits of gold, silver, and other valuable metals.  Its designation as a UN heritage site is a recognition of the deep historical and cultural importance of the region to Mexico.  Originally established as a colony of Spaniards made wealthy by the mines, Guanajuato was the birthplace of the revolution for Mexican independence in the 1800s.  Mining still contributes to its economy.  Guanajuato is also a popular tourist destination for Mexican citizens, and the state of Guanajuato is home to increasing numbers of US expatriates.

Guanajuato is rapidly creating a modern, twenty-first century infrastructure for its citizens with a special focus on the delivery of clean water.  As of ten years ago, the water delivery infrastructure was successful in that it provided water to over 95% of its citizens, but the quality of the water was poor as there was only one water treatment plan and no provisions for the treatment of sewage.  Now, water infrastructure development is brisk with a number of water and wastewater plants recently built and more in the works; estimates of ten to twenty million dollars of building are anticipated.

While further testing of Guanajuato’s water is needed, preliminary evaluations of water samples and conversations with citizens revealed a common set of water quality issues.  Due to proximity to the mines, there is a great concern about levels of heavy metals, arsenic, and cyanide in the local water.  Additionally, Iron levels are particularly high in this region, and visual inspection of water samples taken from many locations suggest that much of this escapes current treatment processes.  Guanajuato’s citizens believe the discoloration due to Iron, and its effects on clothing, hair, and porcelain to be a major water quality issue that the city should address.  Finally, biological contamination of water remains an ongoing challenge and has direct impact on public health as well as the tourism market (e.g. “Montezuma’s revenge”).  While the water treatment plants use chlorine disinfection, by the time the water reaches a tap there is ample opportunity for contamination in the distribution system and aging pipes.

Rice’s capabilities in innovative water treatment processes

Nanoscale materials and the technologies provide a suite of new capabilities applicable to water treatment.  We believe the impacts of these innovations will range from near-term, evolutionary improvements to existing processes to longer-term concepts for wholesale transformation in water treatment that will lower the footprint, both in land and energy use, of water treatment plants.  Some of the key discoveries and capabilities from the various groups are briefly highlighted below.

Nanocrystalline iron oxide powders are a form of high surface area iron minerals that have strong and irreversible interactions with radionuclides, arsenic, and cyanides.  Iron-coated sands have been used for centuries to removed certain metallic and non-metallic contaminants from water and these ‘nano’ versions improved upon older materials in that for the same mass there is much, much greater capacity for sorption.  In several grams of this material, roughly the amount you could hold in the palm of your hand, there is enough surface to cover a football field.  When used as a component in a fixed bed filter, net contaminant levels in processed water are lower, and the quantity of bed materials for disposal is greatly decreased.  Dr. Colvin’s research group has developed extremely simple and cheap ways of making large amounts of these materials, and Dr. Tomson’s research group has quantitative models that describe their anticipated sorption properties in complex aqueous environments.

Nanocrystalline iron oxide powders can be ‘activated’ by the addition of  simple reagents to form reactive sorbents that not only sorb unwanted contaminants but also react with them to yield less toxic species.  Manmade organic contaminants, such as TCE and PAH, are difficult to remove from contaminated wells.  Reactive iron particles, conventionally referred to as zero-valent iron, offer the possibility to reduce these species because of specific surface redox processes that occur at their reactive surfaces.  However, the high reactivity of the materials pose significant problems for their use in that transport and lifetime are compromised.  Dr. Colvin’s laboratory has developed a method that takes inert iron oxide particles and uses molecular reagents that activate them into highly reactive green rust capable of extremely rapid and complete degradation of organics.

The magnetic removal of nanocrystalline iron oxide opens up a new capability for magnetic separation in water treatment systems.  Magnetic separations are widely used in industrial processes for separating a magnetic solid fraction from a liquid stream via an applied magnetic field.  Because the separation does no rely on any interaction with a solid surface, as is the case in physical filtration, it can be completed rapidly, efficiently, and - if permanently handheld magnets are used – without the need for any power.  Drs. Colvin and Tomson’s research groups found that because nanoscale materials interact more strongly with applied fields than their larger counterparts, the separation speed is particularly fast for these materials.  By using magnetic processes instead of settling and filtration to remove solids and/or contaminants, water treatment could be much faster - a compatibility that would translate into much smaller and cheaper footprints for next generation water treatment plants.

Membrane lifetimes and performance can be greatly enhanced by the addition of silver nanoparticles.  Membrane separations are of increasing interest in water treatment because they enable much smaller and more effective water treatment in some cases.  A major issue for their application is the expense and complexity of their application, a problem that centers directly on the fouling of membrane surfaces over time.  Biological contamination is one source of fouling and ultimately membrane failure.  Drs. Li and Alvarez’s laboratories have a method to integrate antimicrobial silver particles into microfiltarion membranes in order to expand their utility in disinfection and increase their lifetime.