Environmental Engineering Reference
In-Depth Information
Hematite
TOC = 0 ppm; 10 mM KCl
TOC = 2 ppm; 10 mM KCl
TOC = 2 ppm; 1 mM CaCl2
TOC = 2 ppm; 8 mM CaCl2
20
10
TiO
2
SiO
2
0
-10
-20
-30
-40
Figure 16.7
Effect of Suwannee River NOM (measured as total organic carbon, TOC),
monovalent salts (KCl) and divalent salts (CaCl
2
) on zeta potential of a representative
natural NM (hematite) and two engineered NMs (titanium and silica dioxide-from
Aldrich) at pH 7.8 (Zhang, 2007).
16.6.1
Sources and Removal of NMs during Wastewater Treatment
Numerous commercial products (e.g., clothing, bandages, food container linings,
etc) contain nano-scale silver metal (nano-Ag) to prevent microbial activity. In one
study, clothing products (athletic and lounge socks) were washed in distilled and tap
water and confirmed that silver, in both nano-Ag and ionic forms, were released into the
wash water (Benn and Westerhoff submitted). The nano-Ag material was on the order
of 500 nm in size containing many nano-Ag primary particles on the order of 20 to 100
nm in diameter aggregated together. Because over 70% of the US population is served
by centralized wastewater treatment systems, this type of wash water containing silver
will end up in sewage that enters wastewater treatment plants (WWTPs). Within the
wastewater treatment plant the processes that may lead to removal of silver, originating
from commercial products containing nano-Ag, should be affected by the following
processes:
1.
Dissolution of nano-Ag into ionic silver;
2.
Sedimentation of nano-Ag in primary settling tanks at the WWTP; and
3.
Partitioning of nano-Ag, and/or ionic silver, onto bacteria biosolids during
activated sludge treatment, and their subsequent removal during secondary
clarification
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