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Current and Potential Applications for Water and Wastewater
Treatment
Nanomaterials are typically defined as materials smaller than 100 nm in at least one
dimension. At this scale, materials often possess novel size-dependent properties different from their large counterparts, many of which have been explored for applications in water and wastewater treatment. Some of these applications utilize the
smoothly scalable size-dependent properties of nanomaterials which relate to the high
specific surface area, such as fast dissolution, high reactivity, and strong sorption.
Others take advantage of their discontinuous properties, such as superparamagnetism,
localized surface plasmon resonance, and quantum confinement effect. These applications are discussed below based on nanomaterial functions in unit operation processes
(Table 13.1). Most applications discussed below are still in the stage of laboratory
research. The pilot-tested or field-tested exceptions will be noted in the text.
Adsorption
Adsorption is commonly employed as a polishing step to remove organic and inorganic contaminants in water and wastewater treatment. Efficiency of conventional
adsorbents is usually limited by the surface area or active sites, the lack of selectivity, and the adsorption kinetics. Nano-adsorbents offer significant improvement
with their extremely high specific surface area and associated sorption sites, short
intraparticle diffusion distance, and tunable pore size and surface chemistry.
Carbon-Based Nano-Adsorbents
Organic Removal
CNTs have shown higher efficiency than activated carbon on adsorption of various
organic chemicals [5, 6]. Its high adsorption capacity mainly stems from the large
specific surface area and the diverse contaminant-CNT interactions. The available
surface area for adsorption on individual CNTs is their external surfaces [7, 8]. In
the aqueous phase, CNTs form loose bundles/aggregates due to the hydrophobicity
of their graphitic surface, reducing the effective surface area. On the other hand,
CNT aggregates contain interstitial spaces and grooves, which are high- adsorption
energy sites for organic molecules [9, 10]. Although activated carbon possesses
comparable measured specific surface area as CNT bundles, it contains a significant
number of micropores inaccessible to bulky organic molecules such as many antibiotics and pharmaceuticals [11, 12]. Thus, CNTs have much higher adsorption
capacity for some bulky organic molecules because of their larger pores in bundles
and more accessible sorption sites.
Current and Potential Applications for Water and Wastewater Treatment
Current and Potential Applications for Water and Wastewater
Treatment
Nanomaterials are typically defined as materials smaller than 100 nm in at least one
dimension. At this scale, materials often possess novel size-dependent properties different from their large counterparts, many of which have been explored for applications in water and wastewater treatment. Some of these applications utilize the
smoothly scalable size-dependent properties of nanomaterials which relate to the high
specific surface area, such as fast dissolution, high reactivity, and strong sorption.
Others take advantage of their discontinuous properties, such as superparamagnetism,
localized surface plasmon resonance, and quantum confinement effect. These applications are discussed below based on nanomaterial functions in unit operation processes
(Table 13.1). Most applications discussed below are still in the stage of laboratory
research. The pilot-tested or field-tested exceptions will be noted in the text.
Adsorption
Adsorption is commonly employed as a polishing step to remove organic and inorganic contaminants in water and wastewater treatment. Efficiency of conventional
adsorbents is usually limited by the surface area or active sites, the lack of selectivity, and the adsorption kinetics. Nano-adsorbents offer significant improvement
with their extremely high specific surface area and associated sorption sites, short
intraparticle diffusion distance, and tunable pore size and surface chemistry.
Carbon-Based Nano-Adsorbents
Organic Removal
CNTs have shown higher efficiency than activated carbon on adsorption of various
organic chemicals [5, 6]. Its high adsorption capacity mainly stems from the large
specific surface area and the diverse contaminant-CNT interactions. The available
surface area for adsorption on individual CNTs is their external surfaces [7, 8]. In
the aqueous phase, CNTs form loose bundles/aggregates due to the hydrophobicity
of their graphitic surface, reducing the effective surface area. On the other hand,
CNT aggregates contain interstitial spaces and grooves, which are high- adsorption
energy sites for organic molecules [9, 10]. Although activated carbon possesses
comparable measured specific surface area as CNT bundles, it contains a significant
number of micropores inaccessible to bulky organic molecules such as many antibiotics and pharmaceuticals [11, 12]. Thus, CNTs have much higher adsorption
capacity for some bulky organic molecules because of their larger pores in bundles
and more accessible sorption sites.
Current and Potential Applications for Water and Wastewater Treatment