Nanotechnology for Water Treatment

Around 76 million people have no reliable access to clean and safe water. The unsafe water and improper sanitation caused over 68,000 children die each year from Diarrhea in India (as Per Civil Society Report). Drinking water contaminants are mainly categorized under i) physical contaminants those fundamentally affect the physical appearance or other physical properties of water. ii) chemical contaminants comprises nitrogen, salts, pesticides, metals, poisons from microscopic organisms, human or animal drugs. iii) biological contaminants are microorganisms in water such as bacteria, viruses, protozoan, and parasites. iv) there are reports of radiological contaminants mainly including caesium, plutonium, and uranium. Nano technology can address the above challenges by two prominent ways-nano-filtration (NF) and nano-adsorbent [1]. Nanoadsorbent and nano membranes technology as shown in Figure 1 can be useful for the removal of heavy metals and toxic ions with disinfecting microbes.

Figure 1:Classification of nanotechnology for water treatment.

Nano adsorbent

Adsorption is considered as an affordable and easy method for water treatment on account of its ease and value adequacy. Adsorbents that are extensively utilized for the removal of contaminants are mainly developed from natural materials and activated carbon. The adsorption process occurred through nanomaterial for water treatment may take place by i) mass exchange of contaminant to the outer surface of the adsorbent, ii) contaminant adsorption onto outside surface of the molecule and iii) intra-molecule dispersion of the contaminant from external surface and conceivable interchange with elements on pore surface within particles. For efficient adsorption of toxic ions, the adsorbent appears to be depending on features like capability to adsorb from aqueous solution, pH range, adsorbent stability, capacity, rate and cost-effectiveness [2].

The adsorption process characterizes the following steps:

A. Disposal of saturated/spent adsorbent is required

B. Effect of pH and temperature are important

C. Not often requirement of post-treatment

D. Removal efficiency of contaminant varied depending upon the adsorbent

E. Process is economic and easy to operate

Arsenic, Fluoride and Nitrate (AFN) are the most common pollutants in Indian scenario and some adsorbents have shown significant potential to remove AFN. γ-Fe2O3 (Maghemite) nanoparticles have been successfully tested for simultaneous removal of AFN where sorption capacity of γ-Fe2O3 nanoparticles was found more than 90% for fluoride removal. Activated aluminum oxide (AA) has been effectively applied for AFN removal from water [3-5]. Regular AA adsorbents have undefinable pore structures beside less sorption capability. Another metal oxide like, Al-Fe (hydr) oxides and Mn-Al binary oxide have also been observed for removal of inorganic contaminants from water. Few nanocomposites such as deposition of nZVI on CNTs, has good possible for quick and efficient removal of nitrate in water. It is important to note that selection of nano adsorbents depend on better surface area, physical property, chemical property, dissolvability of holding materials, nanoparticles leaching into treated water, separation procedure of nanoadsorbents after water treatment, field relevance, natural effect, cost viability, and hazard evaluation. Recyclability of nano-adsorbent requires more exploratory research.

Nano membranes (NM)

Nanofiltration membranes are basically pressured driven process and are characterized depending upon the chargebased repulsion mechanism permitting the separation of ions. Membranes are mainly applicable to reduce the colour, heavy metal ions, hardness and odour from water. The available sea water can also be converted into potable water (desalination). The NM is also prepared in the form of nanocomposite membranes which can be taken as mew form of filtration materials. This membrane consists of mixed matrix membranes and surface-functionalized membranes. The nanofillers (inorganic) which are having higher surface and providing a better surface to mass ratio were embedded in the polymer [6]. The mechanical strength and thermal stability of the membranes can be increased using metal oxide nanoparticles. Like any alternative membrane processes, the NM is facing membrane fouling problem which is one of the major problems. So, to understand the fouling mechanism and to investigate an acceptable control option is one of the essential elements during the membrane application [7]. In recent years fouling has been controlled by flocculation and magnetic ion exchange methods [8].

Various water treatment technologies are based on the primary, secondary and tertiary process. Each process has its own limitations for meeting the challenges of water treatment. There are serious concerns for balancing durability, demand, energy consumption, and commercial competitiveness. However, nanotechnology-based treatments (Nanoadsorbent and nano membranes) have shown the potential for water treatment but very few have reached to commercial scale. Since low production cost is crucial to ensure their widespread applications it’s important to meet the competitiveness through economic efficiency as well as effect on human health.

Support from Department of Science and Technology, Ministry of Science and Technology, Government of India is gratefully acknowledged.

1. Mehwish N, Kausar A, Siddiq M (2014) Advances in polymer-based nanostructured membranes for water treatment. Polymer-Plastics Technology and Engineering 53(12): 1290-1316.
2. Patel RK, Kumar S, Chawla AK, Mondal P, Singh N, et al. (2019) Elimination of fluoride, arsenic, and nitrate from water through adsorption onto nano-adsorbent: A Review. Current Nanoscience 15.
3. Bhatnagar A, Kumar E, Sillanpää M (2011) Fluoride removal from water by adsorption-a review. Chemical Engineering Journal 171(3): 811-840.
4. Jadhav SV, Bringas E, Yadav GD, Rathod VK, Ortiz I, et al. (2015) Arsenic and fluoride contaminated groundwaters: A review of current technologies for contaminants removal. J Environ Manage 162: 306-325.
5. Bhatnagar A, Kumar E, Sillanpää M (2010) Nitrate removal from water by nano-alumina: Characterization and sorption studies. Chemical Engineering Journal 163(3): 317-323.
6. Feng C, Khulbe K, Matsuura T, Tabe S, Ismail AF (2013) Preparation and characterization of electro-spun nanofiber membranes and their possible applications in water treatment. Separation and purification technology 102: 118-135.
7. Meng F, Chae SR, Drews A, Kraume M, Shin HS, et al. (2009) Recent advances in membrane bioreactors (MBRs): Membrane fouling and membrane material. Water research 43(6): 1489-1512.
8. Shon H, Phuntsho S, Chaudhary D, Vigneswaran S, Cho J (2013) Nanofiltration for water and wastewater treatment-a mini review. Drinking Water Engineering and Science 6(1): 47-53.