Remediation Technologies - Environmental Investigation and Remediation - page 358

determined that the photocatalytic decomposition rate of 1,4-dioxane was increased when a voltage
swing of 0.4 V was applied, and formation of toxic intermediates was suppressed.

Ex situ photocatalytic treatment of 1,4-dioxane in extracted groundwater is a demonstrated tech-
nology, as described in the trade literature ( www.purii cs.com ). Several case studies are presented,
with inl uent 1,4-dioxane levels as high as 1500

±

g/L.
An ex situ advanced oxidation system evaluation was performed by Wannamaker (2005),
where cost and anticipated performance were compared between systems utilizing hydrogen
peroxide

μ g/L and post-treatment levels of below 3 μ

titanium dioxide (photo-
catalytic oxidation). Additionally, bromate production was evaluated for each of the technolo-
gies. Field tests of the ultraviolet

+ ultraviolet, hydrogen peroxide + ozone, and ultraviolet +

titanium dioxide system were performed that yielded a
1,4-dioxane decrease from 150 to less than 1.9

+

μ g/L (the detection limit). Bromate conversion,

from naturally occurring bromide at 600 μ g/L, was minimal in the efl uent from the ultravio-

let + titanium dioxide system.

7. 7. 8 O ZONATION
Kishimoto et al. (2005) studied ozonation combined with electrolysis for COD removal from 1,4-
dioxane solution. They dei ned the destruction pathway as starting with hydroxyl radicals produced
through ozonation near the cathode, in a high-pH environment. Additional cathodic ozone reduction
occurred, which helps destroy the 1,4-dioxane. Ozone was noted to then destroy the 1,4-dioxane
degradation products produced in the initial stages. Carbon dioxide produced by the oxidation of
organics typically forms bicarbonate, which inhibits 1,4-dioxane oxidation; however, this process
was mitigated by using a two-compartment l ow cell to strip off the carbon dioxide in the anodic
cell. Chlorine, produced from the oxidation of chloride at the anode, was found to enhance oxida-
tion of the degradation by-products in a one-compartment l ow-cell test.
Suh et al. (2005) used a palladium (Pd) catalyst deposited on activated carbon to evaluate 1,4-
dioxane oxidation using ozone, ozone Pd catalyst. No signii cant concen-

tration decreases were observed with ozone alone (Figure 7.14), and there were no signii cant

+ peroxide, and ozone +

Catalyst + O 3 H 2 O (3.52 mM)O 3 Only O 3

100

80

60

40

20

0

0 10 20 30 40 50

Time (min)

FIGURE 7.14 Destruction of dioxane during oxidation experiments for three different sources of oxidant;
pH = 10; ozone dosage = 10 mg/min. (From Suh, J.H., Kang, D.J., Park, J.D., and Lee, H.S., 2005, Proceedings
from the 9th Russian-Korean International Symposium on Science and Technology [KORUS].)