Biological Treatment of Vegetable
Processing Wastes
GARY E. GRAY, Graduate Student
S. K. BHAGAT. Head
DONALD E. PROCTOR, Professor
Department of Civil Engineering
Washington State University
Pullman, Washington 99163
INTRODUCTION
Cedergreen Frozen Foods, Inc., is a fresh-frozen vegetable packing corporation with
plants operating in Snohomish and Wenatchee, Washington. Both plants have
approximately the same processing season. Green peas are process in July and August
during which a brine separation is employed which consumes approximately 15,000 pounds
of NaCl per day, some of which enters the wastewater stream. Corn and lima beans are
processed during August and September producing the strongest wastewater in terms of
dissolved organics and suspended solids. Carrot processing is carried out principally during
November. Approximately 1,200 pounds per day of heated sodium hydroxide is used to
peel the carrots which raises the wastewater pH to levels between 10 and 12 during that time.
All processing wastewater which averages between 0.5 and 0.6 MGD is passed through
a 20 mesh vibrating screen prior to treatment. The plant currently releases its wastewater
into the City's treatment system which consists of primary sedimentation, chlorination and
effluent disposal into the Columbia River.
Cedergreen's future plans call for the construction and operation of its own wastewater
treatment facility, which likely will consist of an aerated lagoon with separate sludge
reaeration and return capability. Upon final clarification the effluent is to be discharged
into the Columbia River.
A laboratory scale pilot plant study sponsored by Cedergreen Foods was undertaken
by Washington State University to provide the consulting engineer retained by Cedergreen
with the necessary data for design of such a facility. The investigation included the
determination of the most suitable hydraulic detention period and various constants of
metabolism such as endogenous respiration rates, substrate removal rates, oxygen uptake
rates and sludge growth rates, among others. Also of importance was analysis of the raw.
waste samples for various parameters such as COD, BOD, suspended solids, pH, nutrient
contert and total solids; and most probably quality of the treated effluent from an aerobic
biological system.
SUMMARY OF TREATMENT THEORY
Substrate Removal
The Michaelis-Menten rate equation,
, .       Rmax [SI
■Sa+lSl
has been used (1.2,3.4,5) to describe substrate removal rate, R, in completely mixed aerobic
biological systems. When[sJ, the substrate remaining, is quite small in relation to Km, the
substrate concentration at one half the maximum removal rate, the equation reduces to a
first order reaction,
R = f[S]
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