CHANGES IN QUALITY OF LEAFY VEGETABLES AND WASH WATER
IN A SYSTEM EMPLOYING WASH-WATER RECYCLE
R. C. Hoehn, Associate Professor
P. B. Geering, Graduate Student
Civil Engineering Department
M. E. Wright, Associate Professor
W. H. Robinson, Jr., Graduate Student
Agricultural Engineering Department
Virginia Polytechnic Institute and State University
Blacksburg, Virginia 24061
INTRODUCTION
There is considerable interest among United States industries in developing methods
for consolidating and reducing waste loads within their operations so that they can comply
with effluent standards that will be imposed as a result of the National Water Quality
Standards Act Amendments of 1972 (PL 92-500).   As a part of these efforts, an attempt
is being made by industries to reduce freshwater consumption so that both the costs required to produce their product and the waste volumes they generate in their operations
can be minimized.
Food processors, according th the National Canners Association (NCA) [1], are major
consumers of fresh water, requiring about 99 billion gallons annually.   Industries that
process leafy greens, the subject of this chapter, use large volumes of water for washing,
cooling, blanching and transporting product.   Bough [2], citing NCA publications, reported
a range of from 8.4 to 9.0 thousand gallons per ton(gal/ton) as the volume of water required for spinach processing in this country.
In April  1976, the Environmental Protection Agency published the effluent guidelines
and standards that will be used by state and federal officials when issuing National Pollutant Discharge Elimination System (NPDES) permits to food processors.   These guidelines and standards, published in the Federal Register [3], were based on.log means of
flow and waste loads at nine plants in the United States.   These means were used in a
simulation model that predicted the performance of various treatment systems, and from
the model output the standards for 1977 were derived.   For spinach processing plants, the
average water flow used in the model was 8000 gal/ton.   The assumed wastewater flow
used in the model for predicting the standards for 1983 (when processor must use the
"Best Available Technology Economically Achievable") was 3140 gal/ton, a flow that was
considered reasonable when good water-use practices are instituted.   It is obvious that
while there are not standards, as such, on water usage rates, it will be to every processor's
advantage to institute good water-use practices in order to consolidate wastes for easy
handling and treatment.
One way to reduce the waste volume in a greens processing operation is to reduce the
volume required for washing the product before it is blanched and either packaged or
canned.   Available estimates of the water volume used during washing range from 50% [4]
to 73% [2] of the total required for complete processing.   Therefore, one obvious way to
reduce the water consumption is to modify the system to permit recycling of the wash
water.   Of course, the chief concern is that such a modification would not cause deterioration of product quality beyond acceptable limits.   However, relatively little is known
about the effects of recycling wash water on product quality.
In 1973 the authors submitted a proposal to EPA that a project be funded to design,
build and test a full-scale, immersion-type washer that would recycle the wash water during greens-washing operations.   The proposed system was to be a modification of an
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