Nanotechnology in water pollution treatment

Bara’a fouad abdul ameer

Introduction:

While everybody talks about oil prices, water scarcity andwater pollution are two increasingly pressing problems thatcould easily and quickly surpass the oil issue. Renewableenergy sources can substitute for fossil fuels – butfreshwater can't be replaced . Water is the most essentialsubstance for all life on earth and a precious resource forhuman civilization. This makes the ability to remove toxiccontaminants from aquatic environments rapidly, efficiently,and within reasonable costs an important technologicalchallenge . Nanotechnology could play an important role inthis regard . Nanotechnology is a field of applied science,focused on the design, synthesis, characterization andapplication of materials and devices on the nanoscale.

Sources of water pollution:1- water used for domestic, commercial and other purposes, such as schools, hotels and restaurants.2- Water industrial uses.3- rainwater. 4- leaking water from several sources, particularly groundwater.

This water contains several solid and dissolved elementsin the form of pollutants:stuck materials , organic materials biodegradable ,live pathogens ,plant nutrients (nitrogen, phosphorus, potassium ),organic materials resistant to degradation ,. heavy metals , soluble metal salts.

Diseases caused by contaminated water:

Malaria, Cholera, Typhoid, Cystitis, NephritisGastroenteritis, Viral hepatitis, Skin diseases(hardened lesions), Goiter.

Water pollution treatment methods:Conventional practices adopted for water purification – whichcan be classified into physical, chemical and biologicalmethods – suffer from certain limitations such as high cost,low adsorption capacity, generation of toxic sludge, etc. Thesetechnologies – which include coagulation, flocculation, reverseosmosis, membrane separation, oxidation and ozonation,adsorption – are expensive or inadequate to remove dye.Adsorption with activated carbons, which is a cheap andeffective method, has been demonstrated to remove dye fromwastewater. But this approach is not suitable for industrialwastewater treatment because activated carbon can only beused once and then it is commonly disposed of in landfills.Moreover, removal of pathogens from treated water requiresadditional processes like chlorination, ozonation, etc., whichincreases the cost of treatment.

Solution :

A possible solution to tackle this problem has been demonstrated by scientists in India. They developed nanotechnology-based water purification using nano-silica-silver composite material as antifouling, antimicrobial and dye adsorptive material. Using this process, pathogenic bacteria and dye present in contaminated water can be treated simultaneously without using any chemicals, high-temperature, pressure or electricity.

Schematic illustration of the in situ synthesis (A) of silvernanoparticles on nano-silica support (NSAgNP) by proteinextract, (B) immobilization of protein coated silvernanoparticles on nano-silica support by the ‘post-deposition’ route.

Scheme of the removal of heavy metals with the humic acid coated Fe3O4 magnetic nanoparticles.

*zero-valent iron, were directed towards the depollution of wastewater It proved to be particularly suitable for the decontamination ofhalogenated organic compounds, the presence of zinc is mainly fromindustrial pollution. Nanoscale zero-valent iron (nZVI) has beeninvestigated as a new tool for the reduction of contaminated water.The heavy metal removal by nZVI generally involves redox,cementation, adsorption and precipitation.The nZVI is the core-shell structure: a single particle composed of adense core surrounded by a thin amorphous shell exhibitingmarkedly less density than the interior core. When nanoscale ironparticles are exposed to water media, they will obtain hydroxidegroups and consequently an apparent surface stoichiometry inproximity to FeOOH is formed.

. The FeOOH-shell could enhance the adsorption. The H+

inhibited the formation of iron (oxy)hydroxide, resulting in thelow removal extent of Zn2+ by nZVI.Accordingly, the high removal extent of Zn2+ by nZVI might becaused by adsorption and co-precipitation, which was provedby the effects of DO and pH. The formation of FeOOH on thesurface of nZVI could be the main factor of Zn2+ removalbecause of its high adsorption affinity for aqueous solutes.

The structure of nZVI during reaction.

Treated water uses:Treated water can be used in several purposes, either directly or indirectly.In general, the re-use of treated water by various sectors ratio are as follows:

1. Agricultural purposes 60% .2. Industrial purposes 30% .3. Other purposes finance groundwater 10%.