Electrodialysis in Waste Water Recycle
J. D. SMITH, Research Engineer
J. L. EISENMANN, Manager, Membrane Technology Section
Ionics, Incorporated
Cambridge, Massachusetts
INTRODUCTION
Ionics, Incorporated, of Cambridge, Massachusetts, initiated studies involving electrodialysis and waste water recycle in 1961 with the support of the USPHS,
Advanced Waste Treatment Research Program. This work began with a study of
ABS removal by ion-exchange resin and membrane processes (1). By mid-1962,
it had become apparent that, although organic removal by ion-exchange or electrodialysis was not inconceivable, other existing processes (e.g., foam fractionation and carbon adsorption) had reached a state of development where they offered more immediate promise for efficient and economical removal of organics
(2,3,4,5). The chief function of electrodialysis in the treatment of waste water
seemed, for the present, to be the removal of inorganics. Accordingly, the emphasis in Ionics' research program was shifted from the effect of electrodialysis
upon organic material (ABS, etc.) to the effect of organic material upon electrodialysis (6). That is, if electrodialysis were to be used for inorganic removal
in waste water recycle, how would suspended and/or soluble organic material affect the cost and performance of the process?
The waste water recycle concept is illustrated in Figure 1. Costs for the
various steps in this cycle are average and prevailing high cost figures taken from
the first summary report (7) of the Advanced Waste Treatment Research Program.
The recycle treatment facility would replace additional source development,
transmission, water treatment, and waste treatment, and so might be an economically attractive consideration if recycle treatment could be accomplished
for around 17 cents/KGal in an average situation, or 35 cents/KGal in a prevailing high cost area. The recycle treatment facility is generally thought of as a
chain of processes following a secondary sewage/waste treatment plant. Some of
the processes (and their estimated costs) which would probably find their way into
such a chain are shown in Table I.
As can be seen, in 1962 the estimated cost for electrodialysis was the largest
single item in the overall treatment cost picture. Any improvement in the precision of electrodialysis cost estimates would have a significant effect upon the
total recycle cost estimate. The electrodialysis research conducted during 1962
and 1963, then, was oriented towards obtaining information which could be used
to relate experimental electrodialysis stack performance to plant design and cost
estimates.
ELECTRODIALYSIS PROCESS DESIGN
The design of electrodialysis equipment has been described by several
writers (8,9,10,11). The procedure of Mason and Kirkham (8) is used in this
report and is outlined briefly below.
Electrical resistance is described in units of ohm-cm2/cell pair. Correlation
of electrical resistance with an averaged solution normality is accomplished with
the relationships:
-  738 -