DYE SENSITIZED PHOTO-OXIDATION OF BROMACIL
IN WASTEWATER
Talbert N. Eisenberg, Graduate Instructor
E. Joe Middlebrooks, Provost and Vice President
V. Dean Adams, Director
Center for the Management, Utilization,
and Protection of Water Resources
Tennessee Technological University
Cookeville, Tennessee 38505
INTRODUCTION
A new approach to wastewater detoxification is to use sunlight and photosensitizers. Sunlight or
ultraviolet radiation is a powerful oxidant by itself; however, ultraviolet radiation from the sun is
mostly filtered out in the earth's atmosphere before reaching the earth's surface. Unless ultraviolet
radiation is produced from ultraviolet lights, the process is not efficient. Sunlight energy in the visible
spectrum can be used for detoxification by using photosensitizing agents and dissolved oxygen. The
sensitizer absorbs energy from visible light and transfers this energy to the oxygen substrate reaction
system where photooxidation occurs.
The term "sensitized photooxidation," also referred to as "photodynamic action," "indirect
photolysis," "photodynamic oxidation," and "photosensitization" is synonymous with oxidation
reactions using singlet oxygen as the oxidizing agent. Photosensitized oxidants have been of interest
to chemists and biologists since Raab's discovery in 1900 that microorganisms are killed by light in
the presence of oxygen and sensitizing dyes [1]. Under these conditions, pathological effects (cell
damage, induction of mutations or cancer, and death) occur as a result of the photoxidation of
sensitive cell constituents.
Many classes of organic compounds are sensitive to photooxidation, including alcohols, nitrogen
heterocyclics, organic acids, phenols, benzenoid and aromatic heterocyclic compounds [2]. Bulla and
Edgerly [3] showed that 2,4,5-T, (2,4,5-trichloro-phenoxyacetic acid), parathion, and IPC (isopropyl
N-phenylcarbamate) can be photooxidized. Matthews [4], Oginsky et al. [5] and others showed that
most microorganisms, including viruses, can be killed by low concentrations of photosensitizing dyes
in the presence of light and oxygen.
In recent years, induced photolytic activity using sunlight or artificial light and dye sensitizers
was successfully used in small scale laboratory experiments to photooxidize bromacil [6], terbacil [7],
uracil herbicides [8], and s-triazine herbicides [9]. Watts [10] developed a mathemetical model based
on factors influencing photooxidation, and excellent correlation with laboratory data was observed.
There are several advantages of dye sensitized photooxidation for detoxification of wastewater.
Energy costs for the system are minimal because the process is energized by a no cost energy source,
sunlight. The sensitizer is regenerated and only trace amounts (1-10 mg/1) are required. Toxic chlorinated organics are not formed. Structural facilities (ponds) and instrumentation associated with these
systems are relatively inexpensive and are simple to design, construct, operate, and manage. In addition, the required contact time for detoxification is relatively short.
An examination of the cited literature has proved that although the disinfection-detoxification
process is effective in laboratory scale systems, further research is needed before full scale systems
can be designed. For example, the hydraulics of laboratory scale systems may differ significantly
from a full scale system, and environmental factors, such as light intensity and influent characteristics
can not be controlled in full scale systems as in laboratory scale systems.
At the present time, insufficient information is available for the design of a full scale solar de-
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