Ozone Disinfection of Combined Industrial and
Municipal Secondary Effluents.
Part II — Pilot Plant Studies
CARL NEBEL
PAUL C UNANGST
RONALD D. GOTTSCHLING
Ozone Systems Division
The Welsbach Corporation
Philadelphia, Pennsylvania
RICHARD L. HUTCHISON
THOMAS J. McBRIDE
DEAN M. TAYLOR
Louisville and Jefferson County Metropolitan Sewer District
Louisville, Kentucky
INTRODUCTION
Previously it had been recorded that the ozone disinfection of municipal secondary
effluents offers many advantages over the use of chlorine (1). A degree of tertiary treatment,
removal of suspended solids, ease and safety of operation, and an effluent that is completely
safe to the receiving stream are among the advantages obtained at no additional cost above
the cost for disinfection. The earlier laboratory results prompted investigations on a larger
scale.
Researchers at the Fort Southworth Sewage Treatment Plant in Louisville, Ky.
investigated the use of several continuous flow contacting systems over a period of ten
months with effluent flow rates in the range of 0.75-4.0 gpm (2.84- 15.0 I/min). A simple
unpacked column utilizing cGunter-current flow techniques gave results in which
inordinately high concentrations of ozone were required to produce desired levels of
disinfection. A two stage reactor system in which effluent and ozone were continuously
mixed with a rotating baffle also gave inconclusive results. A counter-current column
having fifteen mixing chambers fitted with a rotating sprocket mixer (1500 rpm) allowing
counter-current flow gave satisfactory results in terms of microorganism kill and ozone
mass-transfer. Unfortunately, the latter system did not allow the removal of suspended
solids by a flotation process, and it was difficult to scale-up within a reasonable economic
scale. This early work established the maximum ozone dosage level at the Fort Southworth
Sewage Treatment Plant as being 14 mg/1. The object of the study was to exceed the
ORSANCO regulation which required that a secondary effluent be disinfected to a level of
200 fecal coliform/100 ml. The ozone dosage level required to meet this level ranged from 6
to 14 mg/1. This ozone dosage level is much higher than that which is required to accomplish
the same level of disinfection in a standard municipal secondary effluent. Previous
laboratory results employing various effluents indicated an ozone dosage of 7 mg/1 as being
required to produce a fecal coliform density of 200/100 ml. The high ozone dosage level
required at the Fort Southworth plant unquestionably reflects the mixed character of the
plant influent, which has a 60 percent industrial BOD loading. Industrial effluents
invariably contain materials which are not biodegradable. Such refractory materials exert
an ozone demand due to the presence of carbon-carbon double bonds and therefore
increase the amount of ozone required for disinfection.
Ozone is a disinfectant which must be generated on the site of usage and applied
immediately; it cannot be stored. For these reasons the ozone generating facilities of an
ozone plant must be designed for the peak flow periods and maximum dosage levels. The
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