OZONOLYSIS OF WASTEWATERS USING A SPINNING DISC REACTOR
G. K. Anderson, Senior Lecturer
C. B. Saw, Research Associate
Department of Civil Engineering
C. R. Howarth, Lecturer
Department of Chemical Engineering
University of Newcastle upon Tyne
Newcastle, England 0632-328511
INTRODUCTION
If discharge standards are outside the capability of conventional secondary treatment processes,
then the secondary effluents will have to be subjected to 'tertiary treatment.' Many techniques have
been developed for the treatment of secondary effluent, e.g., microstraining, rapid gravity sand filtration, lagooning, carbon adsorption, ion exchange and reverse osmosis. The inclusion of ozonation in
this list has only been considered in recent years but is becoming more widespread, particularly in
Europe, USA, Russia, and Japan.
Most of the conventional tertiary processes do not remove all undesirable highly refractory species. Some of these species, when chlorinated, produce highly toxic products. Recent investigations of
chlorinated hydrocarbons (which are potentially carcinogenic) in water supplies have initiated more
serious consideration of ozone as an alternative treatment to chlorination.
The main aim of this research was to investigate the simultaneous effects of ozone on the major
sanitary parameters such as BOD, TOC, and color in samples obtained from a wastewater treatment
plant (activated sludge system) which treats approximately 50% domestic and 50% wastewater from a
textile finishing plant. A major problem faced by the treatment plant is the presence of strong colors
produced by the textile plant. The final effluent, even after treatment by activated sludge, contains
high levels of a wide range of textile dyes. These dyes appear to be quite resistant to conventional
treatment.
The process of oxidizing water soluble material can be limited either by mass transfer of the ozone
into the water or by the reaction kinetics of the ozone-aqueous system. Ozone is relatively insoluble in
water and hence considerable attention has to be directed towards the most effective methods of
bringing the gas into intimate contact with the water so that maximum absorption may be achieved
and the wastage of ozone reduced to a minimum. A 'Spinning Disc Reactor' developed in the Department of Chemical Engineering, University of Newcastle upon Tyne, U.K., was used as the contactor
in this research. In the past, it has been shown that such a contactor is very efficient in mass transfer
[1], hence a spinning disc contactor was specifically constructed for the tertiary treatment of effluents
using ozone oxidation.
HYDRODYNAMICS OF LIQUID FILMS ON A SPINNING DISC
Much information is available concerning the hydrodynamics controlling the flow of liquid films
formed under the action of gravity on vertical and inclined stationary planes. Such thin films present a
large area for mass transfer. Also, due to the presence of a wave motion (ripples), which is a characteristic of such films, the rates of heat and mass transfer are increased. This is caused by the turbulence due to the interfacial waves and by an increase in the interfacial area of the film, hence the internal resistance to heat and mass transfer is minimized.
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