EVALUATION OF A WASTEWATER TREATMENT PROCESS
BY A NEW TECHNIQUE
M. L. Jackson, Professor
Department of Chemical Engineering
University of Idaho
Moscow, Idaho 83843
INTRODUCTION
Equations are presented which permit the use of phase analyses of a biological process for the
determination of oxygen transfer efficiencies, volumetric transfer factors, alpha values, and desorp-
tion of gases from liquids for flotation. Concentrations of oxygen, nitrogen and carbon dioxide in
the molecular state were determined using a new technique of sample equilibration in combination
with a gas chromatograph. The analyses and equations have been applied to a complete mix activated
sludge process, the deep tank aeration/flotation (DTA/F) system, where reliable samples of gases
and liquids can be obtained.
A pulp/paper mill is expanding production which will increase the BOD waste load on the existing
(DTA/F) treatment system. A study was undertaken to evaluate the potential of the present system
to treat the loading at increased mill production. The system has been meeting discharge requirements
over the past eight years.
Recent modifications of the process include operating at an elevated temperature of 48-51 °C and
at near zero dissolved oxygen in the bulk tank liquid. Initial data demonstrate the application of the
equations and techniques developed. Performance of the system confirms the increased oxygen transfer and BOD utilization expected.
TREATMENT SYSTEM
A thermal mechanical pulp (TMP) mill produces newsprint and off-set paper from wood chips.
The original (DTA/F) treatment process (deep tank aeration/flotation), was installed in 1976 when
tonnage production was less than half that at present and the BOD concentration of the effluent was
about 200 mg/1. Increased production and reduced use of water raised the BOD concentration in the
effluent to about 400 mg/1 in 1981 and to over 600 currently (1985). Treatment flow rates have
remained about the same at 0.5 to 0.6 MGD. Thus, the wastewater loading on the treatment process
has increased three times since first installed.
The treatment system consists of a tank reactor 25 feet in diameter with a liquid depth of 32-34
feet and a small flotation unit. For convenience, effluent and sludge discharge streams go to a plant
clarifier used for other plant wastewater of low BOD. All equipment was developed from surplus
from an abandoned pulping process and so was not designed for a specific loading. However, except
on a few occasions, the system has permitted the plant to meet discharge limitations to an adjacent
river. Expansion by adding a refiner employing the CTMP (chemical thermal mechanical pulping)
process will add substantially to BOD loadings.
A study of the present status of the treatment system to recommend changes for increased treatment capacity was undertaken in the Fall of 1984. The plant and treatment process have been described [1,2].
EQUATIONS FOR EVALUATION OF REACTOR PERFORMANCE
The flow sheet for the (DTA/F) system, Figure 1, includes some of the nomenclature given in
that section. The streams which are measured and controlled are the feed to the tank and the sludge
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