Pretreatment of a Highly Organic Industrial Wastewater
— Case History
MICHAEL S. GOULD, Research Fellow
Department of Environmental Science
Rutgers University
New Brunswick, New Jersey 08903
ALBERT R. ROY, Manager of Consulting Services
Princeton Aqua Science
New Brunswick, New Jersey 08902
E.J. GENETELLI, Professor
Department of Environmental Science
Rutgers University
Brunswick, New Jersey 08903
INTRODUCTION
Commencing in December, 1972 an industrial wastewater pretreatment facility was
started up at a large chocolate candy producer. Previously, the wastewater was pretreated
for grease removal and spray irrigated. Because of the residential buildup around the spray
fields and the proposed construction of a nearby regional authority treatment plant, a
decision was made to discharge to the regional system. Due to Environmental Protection
Agency and local authority requirements, further pretreatment was necessary.
INITIAL STUDIES
The existing grease removal process was studied to determine optimal alum and lime
dosages concurrent with a wastewater characterization study. The grease removal system
consisted of flotation tanks equipped with skimmers and scrapers, and chemical feeders.
Samples were flow composited over 8 hour periods for 14 consecutive days. Results
indicated that the wastewater organic strength and color were extremely variable and the
two hour detention period in the grease removal flotation tanks provided some equalization. Although the level of production and the products produced remain constant,
the processes are batch types. Suspended solids, 5-day BOD, COD, and grease were
determined on the flotation tank influent and effluent. Table I contains these results. The
alum and lime dosages were 30 and 20 mg/1, respectively, at a flotation tank rise rate of
approximately 1 gpm per sq ft. Higher grease removals could be attained at higher dosages,
but the increased volumes of sludge made it unattractive.
Laboratory bench scale studies were used to determine biodegradability of the
wastewater and to make approximations of process parameters. Because the wastewater
was thought to be highly degradable and any chosen system would be piloted first, the
decision was made to use batch feed acclimatization and kinetic studies.
The procedures used were generally as presented by Eckenfelder in his publications (1,
2) concerning industrial wastewater biological system design utilizing batch kinetic studies.
Raw wastewater was neutralized to pH 6.5 to 7.5 and inorganic nutrients added to maintain
a minimum C/N/P ratio of 100/5/1. All subsequent studies were performed with nutrient
addition.