Using nanoparticles to remove pollutants and contaminants from wastewater

201306047919620(Nanowerk News) The Fraunhofer Institute for  Interfacial Engineering and Biotechnology IGB and its European partners have  developed several effective processes for eliminating persistent pollutants from  wastewater. Some of these processes generate reactive species which can be used  to purify even highly polluted landfill leachate while another can also remove  selected pollutants which are present in very small quantities with polymer  adsorber particles.
Biological stages in wastewater treatment plants are not able to  remove substances such as drugs, found in the wastewater of medical centers, or  halogenated compounds and cyanides from industrial wastewater. This is why  antibiotics and hormonally active substances such as bisphenol A from plastics  manufacturing have already accumulated in the environment and can be traced in  ground water and even in some samples of drinking water. Such persistent  pollutants require a special purifying treatment to remove them from wastewater.  Our tests have shown that oxidative processes with hydrogen peroxide or ozone as  the oxidizing agent are especially effective.
It is usually necessary to adapt or combine various processes in  order to be able to degrade the many different components present in industrial  wastewater in an effective and efficient manner. The Fraunhofer Institute for  Interfacial Engineering and Biotechnology IGB runs a pilot plant in Stuttgart  for testing standard processes either individually or in any desired  combination. The IGB has added two new methods which generate reactive species,  especially hydroxyl radicals, efficiently. Hydroxyl radicals oxidize pollutants  into smaller, more degradable organic molecules or mineralize them completely to  carbon dioxide. In the first method, reactive molecules are generated  electrochemically in a combined anode/cathode process and in the second by means  of atmospheric pressure plasma. Neither method requires the addition of  additives.
Oxidative electrochemical treatment of landfill  leachate
Within the CleanLeachate project funded by the EU (grant  agreement no 262335),, the Fraunhofer IGB has developed an  oxidative process which does not require additives and which is, thanks to its  electrochemical operating principal, suitable for treating extremely turbid  wastewaters. A consortium of six partners from five European countries is  currently treating highly polluted leachate from landfill sites with a combined  anode/cathode process, in which a membrane separates an electrolytic cell into  two separate chemical reaction areas. Top priority was given to choosing the  most suitable electrode material, especially for the anodes, where the hydroxyl  radicals are generated as reactive species when voltage is applied. The polluted  water flows past the anode where it is oxidized and is then pumped to the  cathode where the components are reduced.
The treatment is now being tested in continuous operation on a  landfill site in Czechia. This has lead to improvements such as the lowering of  the chemical oxygen demand and the overall nitrogen concentrations to below  legal limits and the fulfilment of wastewater regulations. To make the process  ready for marketing, a prototype was automated and made portable to test further  types of wastewater, while gathering experience and reliable data for further  optimization steps.
Open plasma processes for water purification
Another new approach for purifying water involves the use of an  atmospheric pressure plasma. A plasma is an ionized gas containing not only ions  and electrons but also chemical radicals and electronically excited particles as  well as short wave radiation. Plasma can be ignited by means of an  electromagnetic field e.g. by applying high voltage. The plasma glow is  characteristic and can be seen in the fluorescent lamps of neon signs used for  advertising purposes. In a technical sense, plasma processes have already been  used specifically for modifying and cleaning surfaces for a long time now.
Open plasma reactor
Open  plasma reactor. (© Fraunhofer IGB)
This principle is currently being applied by the partners of a  joint water plasma project, funded by the EU, entitled “Water decontamination  technology for the removal of recalcitrant xenobiotic compounds based on  atmospheric plasma technology”, grant agreement no. 262033,,  in which a plasma is used for purifying water in an oxidative process. The  result is a plasma reactor in which the reactive species formed in the plasma  can be transferred directly to the contaminated water. The reactor is “open” so  that the plasma is in direct contact with a flowing water film. The plasma  reactor is designed in such a way that a plasma can be ignited and maintained  between a grounded electrode in the form of a stainless steel cylinder within  the reactor and a copper network acting as high voltage electrode. To do so,  high voltage is applied. The copper network is on a glass cylinder which acts as  a dielectrical barrier, also shielding the reactor to the outside. Polluted  water is pumped upwards through the stainless steel cylinder in the center of  the plasma reactor. When the water flows down the outer surface of the cylinder,  it passes through the plasma zone between the stainless steel cylinder and the  copper network where the pollutants are oxidized.
In laboratory experiments, Fraunhofer researchers were able to  decolor a methylene blue solution completely within a few minutes. Cyanide was  also broken down effectively by 90 percent within only 2 minutes. Based on such  promising results, the process is now being tested on a larger scale. One of the  project partners is working with a demonstrator which can purify 240 liters of  contaminated water in one hour. The results will be used to continually optimize  the design of the reactor and its process controls. The ultimate aim is to bring  the reactor to market together with further partners from industry. The open  plasma process has a high potential due to the fact that there is no barrier  between the plasma, where the oxidative radicals are formed, and the  contaminated water.
Removing trace substances with selective adsorber  particles
Pollutants can also be removed effectively from wastewater with  selective adsorbers. An adsorption stage is particularly effective when  pollutants are strongly diluted, present in low concentrations or highly  specific. The process is also advisable when a wastewater component is degraded  to a toxic metabolite in biological purification stages. In such cases, it could  be better to remove the substance selectively by pre-treating the wastewater  before it reaches the wastewater plant.
To this aim, the Fraunhofer IGB has developed a single stage,  cost-effective process for producing polymer adsorber particles. In NANOCYTES®,  our patented process, functional monomers are transformed into small  nanoscopically sized polymeric adsorber particles, so-called specific polymeric  adsorber particles (SPA)[GDC1] , with a cross-linking agent. The selectivity of  the adsorber particles can be increased by adding the target molecules to be  removed from the water to the mixture. The trick works like this: once the  monomers have been polymerized, the target molecules can be removed from the  adsorber particles. They leave behind a kind of “imprint” which adsorbs the  target pollutants.
These particles possess a high specific surface area and the  particle surface is easily accessible without limitations. In addition this  approach offers a large flexibility in the design of the surface chemical  properties and the adsorption behavior. A large variety of different monomers  (mono-, bi- and trifunctional) can be used. They are selected on the basis of  physico-chemical properties such as solubility, miscibility and non-covalent  interactions with the target molecules. The particle properties can therefore be  tailor-made for special separation problems.
Fraunhofer researchers have been able to remove bisphenol A and  penicillin G selectively from wastewater. The adsorber particles are chemically  and thermically stable and can be used for a wide range of applications e.g. as  a layer in a composite membrane or as a matrix on packing materials. Once the  pollutants have been adsorbed, the adsorber particles can be regenerated and  re-used. An adsorption column is available at the Fraunhofer IGB for research  experiments.
Systems solutions for water supply and water  treatment
These innovative processes for water treatment complement the  Fraunhofer IGB’s portfolio in the fields of water purification and water  treatment. Together with further processes for water treatment and recovering  wastewater components as energy and fertilizing salts, the Fraunhofer IGB is  steadily optimizing wastewater treatment plants and improving DEUS 21, a system  for the semi-decentralized purification of household wastewater.
Source: McGill University

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