TECHNIQUES FOR CONTINUOUS NEUTRALIZATION OF
STRONG ACID WASTES
Robert W. Okey, Senior Lecturer
Kenneth Y. Chen, Associate Professor
Amancio Z. Sycip, Graduate Student
Environmental Engineering Department
University of Southern California
Los Angeles, California 90007
INTRODUCTION
The characteristics of wastewater dsicharged by industrial plants is of great importance
to the operation of domestic biological treatment plants as well as to the ecology of receiving waters.   The pH of the discharged wastewaters is among one of the quality parameters
which may exert significant impact.   The correction of pH in acidic or alkaline waters is,
therefore, a step often required prior to discharge or before biological treatment can be
carried out.
Neutralization is essentially a simple process.   However, it is a fact that many industrial
plants, in spite of the presence of a sophisticated pH control system, find it difficult to
automatically stabilize pH with alkali or lime within the desired range.   This is particularly
so where the flow and pH vary widely with time [1,2].   The use of complex control
mechanisms also entails additional costs and imposes a substantial maintenance burden.
The lack of buffering capacity in wastewater to be neutralized makes the maintenance
of the pH at the desired level extremely difficult, if not impossible.   This appears to be
especially so in cases where pH correction involves the treatment of wastes containing appreciable quantities of strong mineral acids, and in which all background alkalinity is
destroyed.   In many cases the natures of industrial operations themselves do not contribute
materials which can buffer the system in the pH range acceptable for discharge.
This paper contains the results of a laboratory and field study designed to deal directly
with the central problems; i.e., the lowering of the rate of pH change across the critical
region (pH 5 - pH 9) as a function of the added alkali substances.   In addition, the overall
system is designed as simply as possible—one of the basic criterion considered.
The present work describes the effectiveness and economy of a single-stage, single-probe
system employing only on-off controls and utilizing small additions of sodium bicarbonate
acting as a buffer to increase the relative magnitude of buffer intensity or buffer index, (3,
in the critical control range.  (3 is defined as:
dcB dcA
^  "    dpH     ~      dpH
where dcA   and dcg are the number of mole-liters"1 of a strong acid or strong base required to produce a change of one pH unit.
The present work has been designed and carried out to evaluate the efficacy and cost
of a simple single-stage system employing buffer addition specifically for industries with
modest to moderate flows which contain a strong acid only a small fraction of the time.
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