44    ANAEROBIC PRETREATMENT OF CONVENIENCE COOK
AND PARBOIL RICE PROCESSING EFFLUENT
Enos L. Stover, President
Stover <& Associates, Inc.
Stillwater, Oklahoma 74076
INTRODUCTION
Biological treatment of high strength carbohydrate wastewaters by aerobic treatment methods has
often been limited by the variable nature of the wastewater, economics of treatment, excessive sludge
production, macronutrient (nitrogen and phosphorus) deficiency problems, and physical limitations
relative to adequate oxygen transfer and biological solids settling and thickening problems. Anaerobic
treatment of these types of wastewaters can be both technically and economically feasible while
overcoming these problems and limitations. High treatment efficiencies can be achieved anaerobically
with low sludge production rates and associated low macronutrient requirements while producing
biogas (methane) as a byproduct energy source.
Due to these advantages of anaerobic treatment, anaerobic treatability studies were performed on
the effluents from a large rice processing plant. The primary process effluents generated during rice
processing were the parboil effluent and convenience cooker effluent. The parboil effluent consisted
of about 10% to 15% of the plants BOD and suspended solids loading. The majority of the remainder
of the plants effluent consisted of the high strength convenience cooker effluent .This process effluent
was a highly gelatinized starch wastewater which exhibited very difficult handling properties relative
to physical/chemical solids-liquid separation. Therefore, anaerobic treatment appeared to offer significant advantages as a pretreatment alternative to justify a feasibility assessment of this approach
for treatment.
Both process effluents were characterized and subjected to anaerobic treatability studies to evaluate
the applicability of anaerobic pretreatment. A bench-scale hybrid anaerobic reactor (14.5 liter volume) was used to investigate the technical feasibility of anaerobic treatment of the convenience cooker
effluent and the combined effluents. The test results of the characterization program and treatability
studies on the combined effluent are presented herein.
zJJ
EFFLUENT
DDDDD
DDDDD
DDDDD
MM
WkSTEVWTER
RECYCLE
Figure 1.    Schematic of bench-scale anaerobic
system.
46th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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