Large volumes of contaminated wastewater are discharged from different industries, including battery manufacturing, alloy, mining, and electroplating. Wastewater contaminants (toxic heavy metals and other impurities) cause multiple adverse effects on living beings and the environment. Nanotechnology has proved to be an efficient and less expensive tool for industrial water treatment.
The quality of treated wastewater is a vital factor for its reuse, i.e., the recovered water must meet the safety standards for its specific uses.
Several manufacturing processes discharge a huge amount of contaminated wastewater. The type of contaminants present in industrial wastewater depends on the manufacturing process. Industrial wastewater pollutants generally include organic constituents, extreme pH, toxic heavy metals, high salinity, and high turbidity from the presence of inorganic impurities.
Challenges of conventional water treatments
Industrial wastewater treatments include:
- Chemical precipitation
- Ion exchange
- Coagulation and flocculation
- Membrane filtration
These wastewater treatments are sometimes ineffective in removing specific contaminants, such as toxic heavy metals, microorganisms, and oil. Treatment of industrial wastewater requires multiple sequential complicated steps to meet the quality standards of reusable water.
The process of distillation is a guaranteed method to remove water pollutants from contaminated water. However, this treatment process is highly expensive.
The recovery of industrial wastewater does not always require extreme treatment like distillation. For example, in the oil and gas industry, recovered water does not need to be entirely desalinated, providing specific pollutants are completely removed. In these cases, only a targeted treatment method would be sufficient. This removes only specific contaminants and produces good quality water that can be reused.
Many of the existing wastewater treatment technologies have limited intrinsic capabilities. For example, reverse osmosis membranes cannot be used for the recovery of wastewater containing a high concentration of salinity.
The use of adsorbers is restricted to specific compounds with particular functional groups/structures. Most ion exchange surfaces are specific to certain chemicals.
While addressing these challenges, researchers have put together many processes that can instantaneously remove various pollutants and can recover high-value constituents (rare earth elements and nutrients) and energy from industrial wastewater. However, these complex techniques are highly expensive.
Nanotechnology in wastewater treatment
Nanotechnology has become one of the most explored technologies of the 21st century. Unique properties of nanomaterials include:
- High surface to volume ratio
- Small size
- Well-organized structure
- Competence of filtration
These properties help the removal of heavy metals from polluted wastewater. Based on the type of nanomaterial, wastewater treatment is divided into three main groups:
- Nano adsorbents
This treatment involves the photocatalytic activities that include the interaction of light energy with metallic nanoparticles.
The photocatalytic activities destroy microorganisms (bacteria) and organic substances via the reaction with hydroxyl radicals. The materials used in nanocatalysts are typically inorganic materials such as metal oxides and semiconductors.
The ideal absorbent is small, has a large surface area, great catalytic potential, and high reactivity.
Nano-adsorbents are classified based on their adsorption process, i.e., metallic nanoparticle, magnetic nanoparticles, nanostructured mixed oxides, and metallic oxide nanoparticles.
In this treatment, nanomembranes can separate pollutants from the wastewater. These are extensively used for the removal of heavy metals, dyes, and other contaminants.
Nanotubes, nanoribbons, and nanofibers are commonly used nanomembranes. Silver nanoparticles are antimicrobial agents that are incorporated during the treatment of wastewater containing high loads of bacterial contaminants.
Silver nanoparticles and graphene oxide nanoparticles play a dual role, i.e., biofouling prevention (disable bacterial cells), and, due to their hydrophilic nature, they can reduce microbial attachment by forming a strong water layer.
Commonly used nanomaterials for industrial water treatment are discussed below:
- Carbon nanotubes (CNT): CNTs produce electrically conducting membranes. The pore size of the layer is dependent on the type of polymers used to cross-link the CNT. Membrane pore sizes vary from 100 nm to sub-nanometer. These nanomembranes are extensively used for several biological treatments of industrial wastewater and desalination of industrial brine.
- Graphene oxide (GO) nanoparticles: The GO nanoparticles work on the same principle as the transpiration process of a tree leaf, i.e., pulling water through the GO structure while successfully catching solar heat to stimulate the formation of vapor. This technique is used in solar-powered brine desalination.
- Fluorinated silica nanoparticles: Fluorinated silica nanoparticles generates a low-energy surface that possesses high resistance to oil. This is immensely useful during the treatment of oil-containing wastewater, oil refining, and food processing industries.
- Layered nanomaterials: Layered nanomaterials comprising graphene and graphene oxide, MoS2, and MXenes (ultrathin transition metal carbonitrides carbides, and nitrides) are used extensively in industrial water treatment.
Companies that manufacture nano-based technology for water treatment
Mexico-based companies Carbotecnia and Global Proventus offer highly sophisticated equipment for water treatment using different nano-based techniques such as nanofiltration.
Heltec manufactures water treatment products based on nanofiltration, microfiltration, ultrafiltration, and electrodeionization. Heltec products are exported to the US, Germany, England, Canada, and Ireland, as well as Central and South America.
Aquapro manufactures nanofiltration equipment and provides services such as the installation of equipment of water treatment systems.