Photocatalytic Degradation of Lindane in Potable Water Systems Amanda M. Nienow*,+, Irene C. Poyer*, Juan Cesar Bezares-Cruz*, Inez Hua*, Chad Jafvert* *Civil and Environmental Engineering, Purdue University, West Lafayette, IN 47907 +Advanced Concepts

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Photocatalytic Degradation of Lindanein Potable
Water SystemsAmanda M. Nienow,, Irene C.
Poyer, Juan Cesar Bezares-Cruz, Inez Hua, Chad
JafvertCivil and Environmental Engineering,
Purdue University, West Lafayette, IN
47907Advanced Concepts and Technologies,
International, Waco, TX 76710
ENVR 195
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OH QUANTIFICATION
EFFECT OF VARYING H2O2 CONCENTRATION
INTRODUCTION

• Increased terrorist activity in the United
  States and throughout the world has prompted
  concern over the security of the nations water
  sources, purification and distribution systems
  from possible chemical, biological, radiological,
  or nuclear (CBRN) and/or toxic industrial
  chemicals and material (TICs /TIMs)
  contamination. Technologies, such as reverse
  osmosis (RO), used in water purification systems
  for monitoring and providing safe drinking water
  are effective for most compounds at normal
  operating conditions, but there are a number of
  CBRN agents as well as toxic industrial chemicals
  and materials (TICs and TIMs) that are not
  effectively removed by reverse osmosis (RO).  The
  most promising removal technology to use in-line
  as a replacement for current polishing
  technologies have been identified and include
  photochemical processes, such as photocatalytic
  oxidation (PCO).  These technologies will have
  the benefit of enhancing performance, reducing
  the logistical support requirements and
  potentially enabling continuous polishing
  treatment of the RO product water, thus reducing
  the risk of exposure to CBRN, TICS and TIMS.
• PCO can be broadly divided into direct or
  indirect photolysis, and homogeneous (single
  phase - UV/H2O2 or UV/O3) or heterogeneous (two
  or more phases, e.g., UV/TiO2) systems. Direct
  photolysis requires target contaminants to
  possess a chromophore (a functional group on the
  molecule) which directly absorbs light and
  reacts. However, molecules without chromophores
  may participate in secondary photochemical
  reactions based on their interactions with
  free-radicals. In the case of H2O2, free-radicals
  can be generated during photolysis with UV light
  to produce a highly reactive hydroxyl radical
  (OH)
• Similarly, O3 can decompose via photolysis or
  acid-base reactions. The aqueous O3 reaction
  mechanism varies with pH (more alkaline systems
  favor ozone decomposition) and as a result
  produces several different free-radicals
• The efficacy of engineered photochemical
  processes for destroying or transforming chemical
  agents in a homogeneous system (UV/H2O2 or UV/O3)
  has been investigated. Preliminary investigative
  work was completed on the degradation rates of
  the chlorinated pesticide lindane, one of the
  most stable toxic industrial chemicals (TICs).
• Results presented here are for lindane
  degradation via UV/H2O2 testing effects of

Terephthalic acid is commonly used in sonolysis
to determine the concentration of OH 1. In
the presence of the radical, terephthalic acid is
transformed into 2-hydroxyterephthalic acid, a
compound that fluoresces when excited at 315 nm.
Terephthalic acid solutions, with the addition of
H2O2, were irradiated and the products were
detected with a SLM-Aminco Bowman Series 2
Luminescence Spectrophotometer. The concentration
of 2-hydroxyterephthalic acid was then used to
determine the OH concentration.

• The optimal H2O2 concentration with both 0.26 mM
  and 13 mM Lindane was between 1 mM and 5 mM,
  which correlates well with the formation of OH.
• The drop in rate constants at higher H2O2
  concentrations is likely due to recombination of
  OH, also observed in the terephthalic acid
  experiments (see OH Quantification Box).

Irradiated solutions with 5 mM H2O2 produced the
highest OH concentrations. The slower rate with
higher H2O2 additions is likely due to
recombination of OH.
MONITORING BY-PRODUCTS
TESTING EFFECTS OF pH and NOM
1. pH
No buffer

• The fastest photodegradation reaction rates
  occurred between pH 5 and pH 7, conditions most
  closely simulating those of natural groundwater.
• At pH 9, completed without buffer, the pH dropped
  throughout the course of the reaction. Due to the
  change in pH, the observed reaction rate under
  these conditions is not necessarily first order.
• At pH 11, Lindane undergoes hydrolysis. However,
  hydrolysis rate constants are an order of
  magnitude lower than the rate constants obtained
  in these experiments, suggesting that the PCO
  rate constants can be accurately determined by
  preparing basic solutions of Lindane immediately
  prior to use. (Note Upon sitting for several
  days, hydrolysis products were observed in the
  basic Lindane solutions).

• Complete dechlorination of the parent compound
  was confirmed and quantitated based on the known
  moles of Lindane and the expected moles of
  chloride.
• The formation of an unidentified organic acid was
  observed during chloride analysis and suggests
  incomplete carbon mineralization.
• pH dropped significantly suggesting formation of
  H.
• Additional experiments with longer exposure time
  are scheduled.

EXPERIMENTAL METHODS
A Rayonet RPR-100 Photochemical Reactor
(right) is used to irradiate the aqueous samples.
The reactor uses up to 16 lamps with a wavelength
of 254 nm. Eight lamps were used in the
experiments presented here. The photon flux,
determined by chemical actinometry, is 7 ? 10-6
einstein/sec. A 660 mL quartz tube is placed
inside the photochemical reactor. Aqueous
solutions of Lindane ( 0.1 mg/L or 4 mg/L) are
added to the tube and irradiated for up to 20
minutes. Some solutions were buffered to pH
values of 2.8, 7, or 11.2 with phosphate buffers.
5 mL of solution is removed at a series of
reaction times and the contents are either
extracted with an organic solvent (for analysis)
or sacrificed to measure the pH of the solution.
The concentration of the residual parent compound
is determined through gas chromatographic
analysis. Identification of by-products was
accomplished by ion chromatography.
Top View
KEY FINDINGS/CONCLUSIONS
2. Natural Organic Matter (as Humic and Fulvic
Acids)

• Lindane is almost completely mineralized after 45
  minutes of irradiation at 254 nm (with a photon
  flux of 7 ? 10-6 einstein/sec) to form chloride
  ions and small organic acids.
• Lindane does not degrade via direct photolysis or
  by reaction with H2O2 or O3 alone.
• The optimal conditions for removal of Lindane by
  UV/H2O2 are a near-neutral pH, 1 mM H2O2, and
  minimal amounts of dissolved organic matter.
• H2O2 photocatalysis is a viable pathway for
  degrading and removal of organic contaminants
  from potable water.

REFERENCES/ACKNOWLEDGEMENTS
Rayonet RPR-100 Reactor
References 1 Mason, T.J., Lorimer, J.P.,
Bates, D.M., Zhao, Y. Dosimetry in
sonochemistry the use of aqueous
terephthalate ion as a fluorescence monitor.
Ultrason. Sonochem., 1994, 1(2), S91-94. 2
Larson, R. A., Zepp, R. G., Reactivity of the
carbonate radical with aniline derivatives.
Environ. Tox. Chem., 1988, 7, 265-274. 3
Haag, W. R., Yao, C. C. D., Rate constants for
the reaction of hydroxyl radicals with several
drinking water contaminants. Environ. Sci.
Technol., 1992, 26, 1005-1013. Acknowledgements
Advanced Concepts and Technologies,
International and TARDEC (U.S. Army Tank
Automotive Research, Development and Engineering
Center) for funding, and Dr. Changhe Xiao for
assisting with organic synthesis and luminescence
spectrophotometer analysis.

• Humic and fulvic acids slow the photodegradation
  of lindane at 19.2 mg/L total humic and fulvic
  acids, the reaction is just slightly faster than
  the direct photolysis of lindane.
• Humic acid has a larger effect on the rate
  constant than fulvic acid.
• Light attenuation and the scavenging of OH by
  the humic and fulvic acids are the major causes
  of the drop in reaction rate constants. Note
  2 and
  3.