33    A CRITICAL EVALUATION OF THE OZONE/UV
TECHNOLOGY FOR TREATMENT OF WATER
CONTAMINATED WITH ORGANIC POLLUTANTS
Maria B. Skorska, Engineer
Bechtel Environmental
Oak Ridge, Tennessee  37830
Wayne T. Davis, Professor
Civil Engineering Department
The University of Tennessee
Knoxville, Tennessee 37996
INTRODUCTION
An ozone/U V reactor consists of a tank in which compressed air/ozone or oxygen/ozone mixtures are
injected through a diffusing device and bubbled through contaminated water in a holding tank. A
photochemical reaction is introduced in the reactor by the addition of UV lamps in quartz enclosures,
which are immersed in the water. The reactor also functions as a stripper to the extent that volatile
organics (either target compounds or Ihe intermediate compounds resulting from photoozonation) are
stripped during the reaction process. Finally the C02 and CO resulting from mineralization (conversion
of the organics to simple inorganics due to the photoozonation) are also stripped from the reactor.
The objectives of this research were to quantify the degree to which stripping and/or photoxidation
mechanisms were dominant in an ozone/U V reactor for a variety of organic compounds ranging from
easily strippable to nonstrippable organics, and to determine the extent to which those compounds
which were photoozidized were converted to intermediate compounds versus being completely
mineralized.
PREVIOUS WORK
Ozonation with UV radiation, also known as photolytic ozonation or photoozonation, has been
demonstrated to effectively oxidize a large variety of pollutants typically found in contaminated
groundwater, such as halogenated organics, benzene derivatives, aliphatics, etc. The ozone/UV oxidation process can mineralize organics to C02, H20, and other simple compounds, while ozone alone
will only partially decompose such organics to simpler species, but will not result in their total
destruction.'
Although the advantages of the ozone/UV technology have been described in a number of trade
publications, technical information regarding the kinetics of stripping versus the destruction of the
organics due to the ozone/UV reaction is not as available. In 1990 the U.S. EPA published two
reports on a field demonstration of an ozone/UV reactor used for treatment of groundwater.2,3 The
site selected for this field demonstration was considered typical of the type of contaminated sites for
which the ozone/UV technology was considered a practical remedy. The total organic carbon (TOC)
concentration in the water was about 25 mg/L, and the concentration of the priority pollutants (VOCs
and semivolatiles) was about 2% of the TOC concentration. The field demonstration resulted in the
conclusion that the technology was able to remove the target pollutants to satisfy the NPDES standards. It was concluded that stripping was negligible for most of the VOCs present in the water and
that the volatile compounds did not strip in accordance with Henry's law. In addition, the TOC
removal was reportedly low, indicating that intermediate decomposition products were formed. While
the reaction products of phenol decomposition have been studied extensively, the decomposition
products of the majority of the VOCs present in groundwater and the exact mechanisms involved in
the reaction processes are mostly unknown.4"8 There is also evidence to suggest that intermediate toxic
compounds, for example —formaldehyde, may sometimes form9'0 There exists a potential for the
formation of other toxic decomposition products as well, when ozone/UV technology is used for
removal of organics from water.
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
293