Using nanotechnology to treat water

Water is a scarce resource and for many countries, water supplies do not meet demand. Along with the pressure of climate change and population growth, water will become more and more scarce, especially in developing regions.

Moreover, in these areas, the available water often does not guarantee safety for drinking. Worldwide, 884 million people do not have access to safe water supplies; 3.6 million people die each year from water diseases; 98% of deaths from water fall into developing countries; 84% of water-related deaths are between 0-14 years of age; 43% of water-related deaths are due to diarrhea; 65 million people in Bangladesh, India and Nepal are at risk of arsenic poisoning.

The current effort to ensure people have access to clean drinking water according to the UN Millennium Development Goals, to reduce by half the proportion of people without access to safe drinking water by 2015. According to the World Water Assessment Program, water supply must be renovated for 1.5 billion people. Economic or technological measures will often drive approaches to supply water to poor communities. Economic measures often emphasize the importance of regulations, institutions and open markets. The technology approach focuses on making water pumps, filtration systems or new applications such as nanotechnology.

 

The potential of nanotechnology

Unlike other technologies, often derived from a specific science, but nanotechnology is a combination of many science disciplines. Nanotechnology is determined by the scale of operation. Nanoscience and nanotechnology involve studying matter at microscopic dimensions. One nanometer is 1 millionth of 1mm and a human hair is about 80,000 nanometers wide. The size of nano materials is too small to make people difficult to see. Nanoscale allows handling the smallest parts of matter. Operating at nanoscale will bond atoms and molecules to more easily exploit the characteristics of matter. Just like building a model from Lego bricks, we can imagine creating new materials or changing old materials. In applications such as water filtration, materials can be renewed or modified to purify heavy metals and biological toxins.

Nanoscale materials often have different optical and conductive properties than small or large materials of the same size. For example, nano-titanium titanium is a more efficient catalyst than small-sized titanium oxide. Titanium oxide can be used to decompose organic pollutants in water treatment. However, in many cases, the small size of the nanoparticles produced will make the material more toxic than normal.

The key principle of nanotechnology is to reduce water problems, which are to solve technical difficulties to treat pollutants in water , including bacteria, viruses, arsenic, and mercury. Plant protection products and salt. Many researchers and engineers claim that nanotechnology ensures more efficient and sustainable solutions by using nanoparticles to treat less polluting water than traditional methods and requires less labor, capital, land and energy.

Many nanotechnology-based water treatment devices are already on the market, along with other devices about to hit the market or in development.

Nanofiltration has been widely used to treat dissolved salts and pollutants of small size, water softening and wastewater treatment. Nanofiltration acts as a physical barrier, preventing particles and microorganisms larger than the membrane's filter and selectively removing pollutants.

Nanotechnology will contribute to further improvement of membrane technology while also reducing huge costs in the desalination process. Scientists are developing new materials with nano holes that work more efficiently than traditional filters. For example, a South African study has demonstrated that nanofiltration can filter safe drinking water from saline groundwater. A team of scientists in India and the United States has developed carbon nanotube filters that treat bacteria and viruses more effectively than traditional membrane filters.

Attapulgite clay and natural zeolite are also used in nanofiltration devices. They have nano-sized holes and are used in many parts of the world. A study using an attapulgite clay filter to filter waste water from a dairy plant in Algeria shows that this type of membrane can filter organic substances in wastewater to produce safe drinking water. In addition, zeolite is also used to extract toxic organic substances from water and to remove heavy metal ions. Researchers at Australia's Commonwealth Scientific and Research Organization have created hydrotalcite, a synthetic clay that absorbs arsenic and removes arsenic from water. The researchers also proposed a new type of packaging for this product like 'dip tea bag' to serve low-income people ( 'tea bags' can be embedded into water supplies about 15 minutes ago). when drinking). Selling used tea packages to local governments will promote recycling and help treat waste containing arsenic.

Using nanotechnology to treat water

Nano catalysts, magnets and detectors: Nano catalysts and magnetic nanoparticles are examples of nanotechnology that can turn heavy polluted water into drinking water, hygienic and irrigation water . Nanoscale catalysts have more efficient catalytic properties.

They can chemically disintegrate pollutants instead of just pushing them elsewhere, including pollutants where existing technologies are ineffective or costly. Researchers at the Indian Institute of Science in Bangalore have used titanium oxide for this purpose. Magnetic nanoparticles have a large surface area proportional to their volume and can easily be associated with chemicals. In water treatment applications, magnetic nanoparticles can be used to bind pollutants such as arsenic or petroleum to remove pollutants by magnets. Some companies are commercializing these technologies and researchers are still regularly announcing new findings in this area.

Scientists at Rice University in the United States are using 'magnetic nanoparticles ' to treat arsenic in drinking water. The surface area of ​​large magnetic nanoparticles means that magnetic nano can absorb arsenic 100 times the magnetic nano type has a larger surface area. The research team predicted that 200-500mg of magnetic nano can process 1 liter of water. They are developing a method of magnetic nanoscale production from inexpensive household appliances, which will significantly reduce production costs, bringing this product to the community in developing countries.

Along with water treatment capacity, nanotechnology also detects pollutants generated in water. Researchers are developing new sensor technologies that combine small and nanoscale manufacturing to create small, portable and highly accurate sensors that can detect chemicals and substances. biochemical in water. Some of the consortium in the field of research is testing the field of these devices and will quickly commercialize them. For example, a group of researchers at the University of Pennsylvania studied the method of detecting arsenic in water using a nanowire attached to a silicon chip.

Currently, there are a number of typical products born in developing countries and other products originating from other places but closely related to the needs of Southern countries.

1. Nano foam keeps rainwater produced by the Massachusetts Institute of Technology (USA): Polymer compounds and glass nanoparticles are coated on the surface like fabrics to absorb water. Nano foam works more efficiently than traditional materials. Nano foam used to hold rainwater in countries: China, Neepal and Thailand.

2. Magnetic nanoparticles for arsenic treatment produced by Rice University (USA): Magnetic nanoparticles consist of suspended oxide ions in water bound to arsenic, then removed by a magnet. India, Bangladesh and other developing countries have thousands of cases of arsenic poisoning each year due to arsenic-contaminated wells.

3. Desalination membranes produced by University of California, Los Angeles and NanoH ₂ O: Polymer compounds and nanoparticles attract water ions and push dissolved salts. Desalination membranes are already on the market, allowing desalination with lower energy costs than osmosis methods.

4. Nanofiltration produced by Saehan Company (Korea): Nanofiltration is produced from polymers with pore sizes from 0.1 to 10 nanometers. Nanofiltration tested for drinking water in China and desalinated water in Iran require less energy than reverse osmosis.

5. Water rods in nanotubes produced by Seldon Laboratories (USA) : Straw-shaped filters use carbon nanotubes placed on a plastic material with holes. Water purifier to clean drinking water.

Doctors in Africa are using samples of water rods in nano-grids and the final product will be produced in developing countries at a reasonable cost.

6. Common filtration equipment manufactured by KX Company (USA): Filter equipment uses nano fiber layer made from polymers, resins, ceramics and other materials to treat pollutants. Equipment made specifically for community households in developing countries to use. Filtering devices are efficient, easy to use and do not require maintenance.

7. Plant protection equipment made by the Indian Institute of Technology in Chennai and Eureka Forbes (India) Co., Ltd.: This device uses nano-silver to suck and then decompose 3 types of protective drugs. Plants are often found in water supplies in India. Plant protection drugs often exist in the water supplies of developing countries. Pesticide filtering equipment can provide every household in India 6000 liters of clean water every year.

Applying nanotechnology for water filtration equipment

Nanotechnology has been extensively developed over the past decade and can produce many new materials with potential applications such as carbon nanotubes. Carbon nanotubes consist of cylindrical carbon molecules with a diameter of several nanometers - 1 nanometer, equal to 1 millionth of a millimeter.

Carbon nanotubes have different electronic, mechanical and chemical properties as they can be used to filter contaminated water. Scientists at the University of Vienna recently published a study on this new field in the famous journal Environmental Science & Technology.

Carbon nanotubes are more likely to be applied, including treating contaminated water. Many pollutants in the water have strong adhesion to carbon nanotubes and pollutants are removed from polluted water through filters made from this nanomaterial, such as water-soluble drugs. difficult to separate from activated carbon.

Difficulties due to the saturation of filtration devices decrease when carbon nanotubes have a very large surface area (500 m2 / gram of nanotubes), so the ability to retain pollutants is high.

In the past decade, there have been many studies on carbon nanotubes. However, the unusual properties of carbon nanotubes make it difficult to study. Conventional methods show the limited and active results of nanotubes in actual conditions that are still little known. Mélanie Kahm, researcher for this project along with Xiaoran Zhang, thinks that new technologies often come with benefits and limitations for people and environmental quality. A deep understanding of the interactions between pollutants and carbon nanotubes as well as how carbon nanotubes work in the environment are necessary before using them in filtration equipment.

A team of researchers at the University of Vienna's Department of Environmental Geological Sciences is conducting research on the subject. They developed a passive sampling method that provides more reliable data for practical applications because including concentrations that are likely to occur in the environment (often very low). ). In contrast, traditional methods can only handle high concentrations.