Ozone Disinfection of Combined Industrial and
Municipal Secondary Effluents.
Part I — Laboratory Studies
CARL NEBEL
PAUL C. UNANGST
RONALD D. GOTTSCHLING
Ozone Systems Division
The Welsbach Corporation
Philadelphia. Pennsylvania
INTRODUCTION
The current demand for water quality improvement has resulted in a search for new
and improved economically feasible treatment methods. As standards are raised and water
re-use becomes more and more likely, tertiary treatment procedures become necessary.
Recent investigations (1,2) have indicated that secondary effluents disinfected with chlorine
are toxic to aquatic life. A viable alternative to the use of chlorine is ozone for disinfection
and concurrent tertiary treatment.
Ozone, 03, is an unstable gas naturally occurring in the upper atmosphere. It is
responsible for the characteristic sweet odor in the air immediately following an electrical
storm. Because ozone is unstable it cannot be effectively stored or shipped and must be
generated on-site. Commercial ozonators mimic nature by generating ozone by electrical
discharge through air or oxygen. The process produces ozone as a mixture with either air or
oxygen, and the exit gas from the ozonator typically contains 1 percent ozone from air feed
or 1.7 percent ozone using oxygen feed. Other concentrations are possible, but are less
efficient economically. The ozonized gas can then be dispersed into the water to be treated
either by various injection methods or by forcing the pressurized gas through a porous
disperser at the bottom of a treatment tank.
A variety of laboratory studies (3,4,5,6,7,8,9,10) initially demonstrated the
effectiveness of ozone in secondary effluent disinfection and contaminant removal;
however, the lack of uniformity in experimental techniques and methods has made
comparison of data difficult. The goal of this work was to establish the degree of treatment
possible with various ozone dosage levels. Additional information has been obtained in
pilot-scale studies in the cities of London (England) (11), Chicago (12), and Washington,
D.C. (13), where water of potable quality has been produced by ozonization of a variety of
effluents. A pilot study was also recently completed at the Louisville, Ky., Fort Southworth
Sewage Treatment Plant.
Previous work has established that ozone treatment of sewage can be considered at
several dosage levels: 1) as a treatment for primary sewage and storm water overflow (ozone
dosages of 10-100 mg/1 required); 2) as a tertiary treatment to convert secondary effluent to
water of potable quality (ozone dosages >50 mg/1 required); and 3) as a replacement for
chlorine for disinfection whereby a certain degree of tertiary treatment is concurrently
observed (ozone dosages of 5-15 mg/1 required). In this study we have attempted to more
accurately elucidate the ozone dosages required for disinfection and to determine the
effectiveness of removal of specific contaminants in the effluent.
EXPERIMENTAL METHODS
Secondary effluents obtained from the Millville, New Jersey (contact stabilization),
Hatboro, Penna. (standard activated sludge), and Northeast Philadelphia, Penna. (pilot
plant oxygen enriched activated sludge), sewage treatment plants were ozonized in a 6.5 in.
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