Removal of Acetic Acid from Wastewaters
K.J. HIMMELSTEIN, Senior Research Engineer
Environmental Control Systems
The Dow Chemical Company
Midland, Michigan 48640
INTRODUCTION
As wastewater effluent quality standards become more stringent, the methods used to
insure that effluent quality becomes increasingly sophisticated. Physical-chemical methods
now complement and supplant biological treatment. As a result of this, people have become
attuned to what is the specific species of pollutant as opposed to what is its BOD5 or TOC.
With this new awareness of chemical species identification, the realization that industrial
wastes contain large amounts of low molecular weight refractory organic compounds has
occurred. Typical refractories are acetone, formaldehyde, glycolic acid, formic acid, and
especially acetic acid.
It is the intent of this paper to discuss several recently developed methods of treating
wastes containing acetic acid. These methods include activated carbon treatment (two
processes), U.V. catalyzed chlorination, and solvent extraction.
ACTIVATED CARBON TREATMENT
That acetic acid adsorbs on activated carbon has been well documented (1,2, 3).
However, the adsorption is poor compared to other larger organic compounds, say phenol
(<I0% vs ~20% organic weight/carbon weight). Since operational costs are generally
related directly to carbon consumption, there is need for emphasis on both the
improvement of the adsorption characteristics of activated carbon and improvement of
methods of regeneration. Since the former is generally the purview of the manufacturers of
activated carbon, this paper will concentrate on improved methods of activated carbon
regeneration.
Much research has been done recently on this phase of activated carbon usage. Many
methods are known, but the one method commonly employed today is thermal
regeneration. In this method, the exhausted carbon is treated at high temperature to oxidize
the sorbed material and to reactivate the carbon. There are inherent difficulties in this
method of regeneration, however. First, the carbon to be reactivated must be removed from
the carbon column, transported to a furnace and transported back to the carbon column,
and finally placed in the carbon column. The solids handling problems associated with this
process lead to attrition of the carbon supply. Losses of 5% per cycle are regularly reported.
Second, the sorbed material is oxidized in the furnace. Thus, there is no chance for recovery
of the sorbed material. Often, the material removed from the wastewater is valuable
product or raw material.
The use of caustic soda to remove acetic acid from carbon has been well investigated by
Fox, Keller, and Pinamont (1, 2). The waste stream contains both phenol and acetic acid;
here we will be concerned with the efforts to remove acetic acid only.
A schematic of the process as designed is shown in Figure 1. The equipment was sized
to process 100 gal/min of ■brine. After phenol removal, the phenol-free effluent brine was
collected in a pH adjustment tank where HC1 was added to reduce the pH to 3 and convert
the sodium acetate to acetic acid. This acid brine was pumped through the two acetic acid
adsorbers in the series. The effluent was then neutralized and forwarded to the Dow
chlorine manufacturing complex. All 4 carbon columns are 8 ft in diameter by 20 ft high and
made of butyl rubber-lined steel. With 50 sq ft of cross-sectional area, the design flow rate
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