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Graphene and Water Treatment

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Graphene and Water Treatment

Graphene and Water Treatment

1-graphene water-treatment-img_assist-400x300Water treatment is the collective name for a group of mainly industrial processes that make water more suitable for its application, which may be drinking, medical use, industrial use and more. A water treatment process is designed to remove or reduce existing water contaminants to the point where water reaches a level that is fit for use. Specific processes are tailored according to intended use – for example, treatment of greywater (from bath, dishwasher etc.) will require different measures than black water (from toilets) treatment.

 

 

 

 

Main types of water treatments

All water treatments involve the removal of solids (usually by filtration and sedimentation), bacteria, algae and inorganic compounds. Used water can be converted into environmentally acceptable water, or even drinking water through various treatments.

Water treatments roughly divide into industrial and domestic/municipal.

Industrial water treatments include boiler water treatment (removal or chemical modification of substances that are damaging to boilers), cooling water treatment (minimization of damage to industrial cooling towers) and wastewater treatment (both from industrial use and sewage).

1-graphene water-treatment-img_assist-400x300

Wastewater treatment is the process that removes most of the contaminants from wastewater or sewage, producing a liquid that can be disposed to the natural environment and a sludge (semi-solid waste). Wastewater is used water, and includes substances like food scraps, human waste, oils and chemicals. Home uses create wastewater in sinks, bathtubs, toilets and more, and industry donates its fare share as well. Wastewater and sewage need to be treated before being released to the environment. This is done in plants that reduce pollutants to a level nature can handle, usually through repeatedly separating solids and liquids, which progressively increases water purity.

Wastewater treatments usually consist of three levels: a primary (mechanical) level, in which solids are removed from raw sewage by screening and sedimentation. This level can remove about 50-60% of the solids, and is followed by the second level – secondary (biological) treatment. Here, dissolved organic matter that escaped primary treatment is removed, by microbes that consume it as food and convert it into carbon dioxide, water and energy. The tertiary treatment removes any impurities that are left, producing an effluent of almost drinking-water quality. The technology required for this stage is usually expensive and sophisticated, and demands a steady energy supply and specific chemicals. Disinfection, typically with chlorine, can sometimes be an additional step before discharge of the effluent. It is not always done due to the high price of chlorine, as well as concern over health effects of chlorine residuals.

Municipal water consists of surface water and groundwater. surface water, like lakes and rivers, usually require more more treatment than groundwater (water located under the ground). Municipal/community water is treated by public or private water utilities companies to ensure that the water is potable (safe for drinking), palatable (have no unusual or disturbing taste) and sufficient for the needs of the community.

Water flows or is pumped to a central treatment facility, where it is pumped into a distribution system. Initial screening is performed to remove large objects and then the water undergoes a series of processes like: pre-chlorination (for algae control), aeration (removal of dissolved iron and manganese), coagulation (removal of colloids), sedimentation (solids separation), desalination (removal of salt) and disinfection (killing bacteria). Other processes that may be used are: lime softening (the addition of lime to precipitate calcium and magnesium ions), activated carbon adsorption (to remove chemicals that cause taste and odor) and fluoridation (increasing the concentration of fluoride to prevent dental cavities).

As water is both vital for life and in limited supply, many efforts are placed to find technologies that can help ensure the maintainability of water resources. Among the innovative methods that have been researched and developed are:

  • nanotechnology – the use of nanotechnology to purify drinking water can help remove microbes and bacteria. Many nano-water treatment technologies use composite nanoparticles that emit silver ions to destroy contaminants.
  • membrane chemistry – membranes, through which water passes and is filtered and purified. The pores of membranes used in ultrafiltration can be remarkably fine. This technology exists, and efforts are constantly being made to make it more dependable, cost-efficient and common. Membranes’ selective separation grants filtration abilities that can pose as alternatives to processes like flocculation, adsorption and more.
  • seawater desalination – processes that extract salt from saline water, to produce fresh water suitable for drinking or irrigation. While this technology is in use and also holds much promise for growing in the future, it is still expensive, with reverse osmosis technology consuming a vast amount of energy (the desalination core process is based on reverse osmosis membrane technology).
  • Innovative wastewater processing – new technologies aim to transform wastewater into a resource for energy generation as well as drinking water. Modular hybrid activated sludge digesters, for example, can remove nutrients for use as fertilizers, decreasing almost by half the amount of energy traditionally required for this treatment in the process.

What is graphene?

Graphene is a two dimensional mesh of carbon atoms arranged in the form of a honeycomb lattice. It has earned the title “miracle material” thanks to a startlingly large collection of incredible attributes – this thin, one atom thick substance (it is so thin in fact, that you’ll need to stack around three million layers of it to make a 1mm thick sheet!) is the lightest, strongest, thinnest, best heat-and-electricity conducting material ever discovered, and the list does not end there. Graphene is the subject of relentless research and is thought to be able to revolutionize whole industries, as researchers work on many different kinds of graphene-based materials, each one with unique qualities and designation.

Graphene and water treatment

Water is an invaluable resource and the intelligent use and maintenance of water supplies is one of the most important and crucial challenges that stand before mankind. New technologies are constantly being sought to lower the cost and footprint of processes that make use of water resources, as potable water (as well as water for agriculture and industry) are always in desperate demand. Much research is focused on graphene for different water treatment uses, and nanotechnology also has great potential for elimination of bacteria and other contaminants.

Among graphene’s host of remarkable traits, its hydrophobia is probably one of the traits most useful for water treatment. Graphene naturally repels water, but when narrow pores are made in it, rapid water permeation is allowed. This sparked ideas regarding the use of graphene for water filtration and desalination, especially once the technology for making these micro-pores has been achieved. Graphene sheets (perforated with miniature holes) are studied as a method of water filtration, because they are able to let water molecules pass but block the passage of contaminants and substances. Graphene’s small weight and size can contribute to making a lightweight, energy-efficient and environmentally friendly generation of water filters and desalinators.

It has been discovered that thin membranes made from graphene oxide are impermeable to all gases and vapors, besides water, and further research revealed that an accurate mesh can be made to allow ultrafast separation of atomic species that are very similar in size – enabling super-efficient filtering. This opens the door to the possibility of using seawater as a drinking water resource, in a fast and relatively simple way.

Recent commercial activity in the field of graphene water treatments

In November 2014, the Malaysian based Graphene Nanochem that is traded in the AIM of the London Stock Exchange signed an agreement with Singapore-based HWV to develop and commercialize the PlatClean V1 system – a graphene-enhanced water treatment system for the oil and gas industry. In August 2014, the U.S based Biogenic Reagents announced starting a commercial production of graphene-carbon compound based Ultra-Adsorptive Carbon products to replace traditional activated carbon products for air and water purification.

In March 2013, Lockheed Martin announced the development of a new graphene-based water desalination technology, with hopes to commercialize it by 2014-2015. Their system is said to be energy-efficient and include graphene filters with nanoholes to screen salt from water.

Recent research activity in the field of graphene water treatments

In September 2013, researchers from China’s Nanjing University of Aeronautics announced graphyne, an allotrope of graphene, a promising material for water desalination that may even outperform graphene. Its high throughput and rejection of ions and pollutants give it a great potential for this purpose, and it will require lower energy use than traditional technologies. Also in September 2013, researchers from Korea suggested a new simple, high-yield method of synthesizing a new graphene-carbon nanotube-iron oxide (G-CNT-Fe) 3D functional nanostructures. The researchers report that these structures can function as excellent arsenic absorbents.

In May 2013, researchers from the University of El Paso (UTEP) developed a new water-recycling technology based on graphene membranes. The researchers won $100,000 in the University of Texas System Horizon Fund Student Investment Competition and formed a new company called American Water Recycling (AWR) to commercialize this technology. In April 2013, the UK government funded a $5m graphene membrane research at the University of Manchester. The aim of this research was to advance feasibility of desalination plants and other applications. In January 2013, researchers from Rice University and Lomonosov Moscow State University discovered that graphene oxide can quickly remove radioactive material from contaminated water, as it binds quickly to natural and human-made radionuclides and condenses them into solids. This can naturally be useful in contaminated sites cleanup and other applications.

In January 2012, MIT scientists showed (in simulations) that nanoporous graphene can filter salt water at a rate that is 2-3 orders of magnitude faster than current commercial desalination technologies, reverse osmosis (RO). This opens the door to smaller and more efficient desalination facilities.

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