An Evaluation of Persistency for Water Borne Organics
F.L. HART, Assistant Professor
Civil Engineering Department
Worcester Polytechnic Institute
Worcester, Massachusetts 01609
T. HELFGOTT, Associate Professor
R.G. BEDARD, Graduate Assistant
Civil Engineering Department
University of Connecticut
Storrs, Connecticut 06268
INTRODUCTION — CONCERN FROM PERSISTENT ORGANICS
There are organics from both natural and industrial sources that do not degrade
readily nor quickly in the ambient aquatic environment. These materials are commonly
referred to as refractory, bio-refractory, non-degradable, persistent, stable or residual (1).
The occurrence of such materials is evident after extensive exposure to natural and/or
man-made ecosystems (e.g., biological treatment systems such as the activated sludge
process) (2). Refractory organic studies are an important area of research not only because
of the impending necessity for water reuse and zero-discharge (3) but also because of
recent discoveries that residual organics are persisting in potable water supplies.
Hazards that can be incurred from persistent organics are still largely unknown (4, 5);
however, the New Orleans investigations in late 1974 found correlations between chlorinated hydrocarbons in the community water supply and a relatively high incidence of
cancer. These chlorinated hydrocarbons are suspected to have originated from wastewater
discharges into the Mississippi.
This paper discusses a method for quantitatively evaluating persistent organics as a
Refractory Index (R.L). The use of this index in classifying potential or existing industrial
waste discharges can help in preventing the occurrence of accumulating persistent
organic materials in receiving waters and water supplies.
GENERAL REFRACTORY INDEX DESCRIPTION
The R.L value is defined here as a ratio of the oxygen required for biological stabilization in a long term Warburg Respirometer test, an ultimate Biochemical Oxygen Demand (BODu) to the amount of oxygen required for complete oxidation to end products
of C02, H20 and NO,, and called here Ultimate Oxygen Demand (UOD). The UOD
used here does not correspond to the empirical UOD value currently used by the EPA, i.e.,
UOD (sic.) = 1.5 (BOD,) + 4.6 (NH3); refractory organics, organic nitrogen and BOD,
inhibition responses are not included in the EPA version of UOD; this value is therefore
theoretically different. The UOD used in this publication represents the theoretical
ultimate oxygen demand under conditions of complete aquatic ambient biodegradation.
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