TREATMENT EVALUATION OF
A PECAN PROCESSING PLANT WASTEWATER
Ricardo Jacquez, Graduate Student
W. A. Barkley, Associate Professor
Civil Engineering Department
New Mexico State University
Las Cruces, New Mexico 88001
H. G. Folster, Associate Professor
Chemical Engineering Department
New Mexico State University
Las Cruces, New Mexico 88001
INTRODUCTION
Stahmann Farm is the largest American pecan sheller and is located in southwestern
New Mexico.   At the present time close to 5000 tons of pecans are being processed
annually.   It is the wastewater created by these processing operations which has provided
a topic for research.
In processing the pecans a unique, distinct wastewater is created.   Most of the water
is produced through washing and rinsing operations.   Pecans are processed five days out
of the week and the equipment is washed daily.   The wastewater from the processing
plant is a tannin-type waste containing particulates of nutmeats and shells.   Chlorine is
used extensively as a disinfectant.
The wastewaters are collected in a single sewer which transports them to the treatment
facility consisting principally of activated sludge, which is supplemented by screening for
solids and spray-aeration dechlorination.   This investigation is primarily concerned with
the evaluation of the treatment facility.
Tannins are strong organic pollutants because of their high resistance to biodegrada-
tion [1-4] and can be major contributors of undesirable color to natural waters.   Upon
oxidation, tannins produce a reddish-brown color.   Because of this color problem and
the high resistance of biodegradation, tannin wastes ideally should be completely characterized through chemical and biochemical analysis before selecting an appropriate
treatment system.
A review of the literature shows that tannin wastes can be treated by various chemical
and biological methods [5-11].   The most effective of the biological methods is the
completely mixed activated-sludge process.
STAHMANN FARM
Stahmann Farm is located in the Mesilla Valley, a part of the Lower Rio Grande
Valley in New Mexico.   It covers an area of 4000 acres.   There are approximately
200,000 pecan trees on the farm.   Through its nursery operation, Stahmann Farm also
furnishes young pecan trees to other commerical growers in the southwest.
For many years, Stahmann Farm "double cropped" the area between the trees by
planting cotton, lettuce and onions.   Cotton was the last to go because the trees are
now large and the area between the rows is so shaded that row crops no longer prosper.
Pecan Processing
Pecan shelling activities begin by removing hulls, dirt and stick trash using a large
cleaning cylinder which is fed by a gravity-flow hopper.   Here, the pecans are initially
sized according to diameter and length.   Following this process they are placed in cold
storage contained in 2000-lb capacity  crates.
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