24.3 Removal of Pollutants through Sorption/
24.3.4 Removal of Chloro-Organics in Water
Chloro-organics, including chlorinated methanes, ethanes, benzenes, and polychlorinated biphenyls, are a major class of contaminates and several nanomaterials have been used to aid in their remediation [ 36 ]. Trichloroethylene (TCE) and chloroform (CHCl 3 ) are toxic and carcinogenic containments found in water. A study was conducted in Research Triangle Park, NC, in which 1,600 gallons of 1.9 g/L iron nanoparticles were injected into a TCE plume (average concentration of about 14 mg/L) over a period of two days. The pollutants were completely removed within 20 days near the injection well and within 50 days 7.5 m downstream [ 37 ]. Similarly, a fi eld demonstration was performed at a manufacturing site in Trenton, NJ, in which nanoscale palladium-coated iron particles were gravity-fed into groundwater contaminated by TCE and other chlorinated aliphatic hydrocarbons [ 38 ]. Approximately 1.7 kg of nanoparticles were introduced into the test area over a 2-day period,
Figure 24.5 Concentration of phosphate (mg/L) in solution after adsorption by allophane nanoclay. Adapted from [34].
0 0.0 0.2 0.4 0.6 0.8 1.0
10
Contact time (days)
P concentration (mg/L)
20 30 40
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resulting in TCE reduction effi ciencies up to 96 percent over a 4-week monitoring period [ 38 ].
Iron nanoparticles have been encapsulated with silica in order to increase stability and prevent aggregation. Nanocomposite particles synthesized from an aerosol process are shown in Fig. 24.6(a), where the dark spots are zero- valent iron nanoparticles [ 20 ]. Examining the ratio of remaining TCE to original TCE content, Fig. 24.6(b) shows that the synthesized particles are eff ective in dehalogenation of TCE [ 20 ].
Currently the U.S. EPA sets maximum contaminant levels (MCL) of 5 ppb for TCE and 70 ppb for aqueous chloroform (CHCl 3 ) [ 10 ]. Activated carbon
Figure 24.6 (a) Aerosolized silica particles containing iron nanoparticles [20].
(b) Characteristics of trichloroethylene (TCE) destruction using the silica–iron oxide composite nanoparticles. Adapted from [20].
0 0.0 0.2 0.4 0.6 0.8 1.0
20
Time (hr)
M/Mo
Feslica FeEthyl slica
40 60 80 100
(a)
(b)
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fi bers (ACFs) coated with 30–70 percent phenolic resin, which allows for a tailed porous structure, are superior in performance in comparison to granular activated carbon (GAC) [ 10 ]. Increased nanopore volumes (approximately 1.2 nm) and unsaturated surface chemistry interact favorably with chlorinated
Figure 24.7 Breakthrough curves for (a) trichloroethylene (TCE) and (b) chloroform (CHCl3) from both activated carbon fi lters (ACF) and granulated activated carbon (GAC) fi lters. Adapted from [10].
MCL = 5 ppb
Total Volume (L) 0
0 20 40 60 80 100 120 140 160 180 1000 1500
2 4 6 8 10 12 14
Trichloroethylene Concentration (ppb)
GAC Filter Influent
ACF Filter (none detectable)
Chloroform Concentration (ppb)
Influent
GAC Filter
MCL = 80 ppb
Total Volume (L)
ACF Filter 0
0 50 100 150 200 250 300 350 1000 1500
2 4 6 8 10 12 14
(a)
(b)
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hydrocarbons [ 10 ]. Fig. 24.7(a) and (b) shows that tailored ACF fi lters resulted in undetectable (below 1 ppb) TCE and CHCl 3 concentrations [ 10 ]. In addition to using iron and iron oxide, chloro-organics have been eff ectively removed using carbon nanoporous fi bers.
Polychlorinated biphenyls (PCBs), which were previously extensively used in coolants and lubricants in various electrical equipment, are a family of manmade chemicals that contain 209 individual compounds with various toxicity levels [ 39 , 40 ]. The reductive hydro-dechlorination of 2,2′-dichlorbiphenyl (DiCB) has been completed with a high degradation rate using Pd/Fe supported by polymerized membranes, as shown in Fig. 24.8 . More than 90 percent dechlorination of DiCB was achieved in 2 hours with a 0.8 g/L metal loading [ 9 ].
To examine the eff ect of particle size on reactivity and reaction pathway shift, dechlorination of DiCB with bulk Fe particles (approximately 120 μm) coated with Pd resulted in only a 10 percent dechlorination of DiCB, with a high metal loading of 87.5 g/L [ 9 ]. The surface-area-normalized rate constant k SA calculated for the degradation of DiCB was only 0.00011 L/h m 2 , which is over six hundred times lower than that obtained for the membrane supported Fe/
Pd nanoparticles [ 9 ]. Enhanced reactivity is due to the increased number of catalytic reaction sites on the various facets, edges, corners and defects on the nanoparticles.
24.3.5 Removal of E. coli in Water
Iron oxide has been shown to retard the proliferation of bacteria. The incorporation of iron oxide catalyzed ozonation technology increases the retention of bacteria to the surface of membranes, resulting in improved remediation of water. Iron oxide catalyzed ozonation and membrane fi ltration
Figure 24.8 Batch reaction of 2,2′-dichlorobiphenyl with Fe/Pd in polyacrylic acid (PAA)/ polyvinylidene fl uoride (PVDF) membrane at room temperature with 0.8 g/L metal loading. Adapted from [9].
0.0 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07
0.5
Time (h)
2,2’-Dichlorobiphenyl 2-Chlorobiphenyl Biphenyl Carbon Balance
Concentration (mM)
1.0 1.5 2.0
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will combine to improve inactivation and/or removal of bacteria [ 41 ]. The mortality of E. coli in the product water after treatment using the ozonation–
membrane fi ltration process with iron coated nanoparticles 4–6 nm in diameter was 99 percent [ 42 ]. In Fig. 24.9(a), a comparison of the mortality rate of
Figure 24.9 (a) Percent of live and dead bacteria in the permeate after diff erent treatments. (b) Assimilate organic carbon (AOC) concentration after diff erent treatments for the permeate and reject streams. Adapted from [42].
10 20 30 40 50 60 70 80 90 100 0
% Bacteria counts Membrane filtration
Ozonation Ozonation+Membrane
filtration Catalytic Ozonation+Membrane
filtration
% Live Bacteria % Dead Bacteria
0
Membrane filtration
AOC concentration (mg/L)
Ozonation
Permeate Stream Reject Stream
Ozonation + Membrane filtration
Catalytic Ozonation + Mebrane
filtration 2
4 6 8 10 12 (a)
(b)
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E. coli is made between various membrane treatment processes [ 42 ]. The improved disinfection observed using the combined process is due to the catalytic decomposition of ozone at the iron oxide surface, which resulted in the formation of –OH or other radical species that inactivate the bacteria near the surface. In addition, assembled organic carbon (AOC) concentrations were reduced using the combined process (as shown in Fig. 24.9(b)), indicating that there is a reduced potential for regrowth in water treatment using the coated membranes [ 42 ]. Due to the inactivation of E. coli and the lowering of AOC concentrations using iron oxide catalyzed ozonation technology is likely to be very eff ective to disinfect and control bacterial regrowth in water.