Electrolytic Control of Anaerobic
Waste Treatment Processes
FREDERIC C. BLANC, Assistant Professor
Department of Civil Engineering
Northeastern University
Boston, Massachusetts 02115
INTRODUCTION
Anaerobic treatment processes have provided an effective and economical means of
stabilizing the concentrated wastewaters of certain industries and various types of organic
sludges. The major portion of the municipal sewage sludge in North America is
anaerobically treated. However, the full potential and capacity of anaerobic treatment is
not being utilized due to a lack of understanding of the process and inadequate process
monitoring and control. Automated process monitoring is possible by continuously
measuring electrode potentials in the anaerobic solution. It has been demonstrated (1.2,3)
that electrode potential measurement is a monitoring parameter for the methane
fermentation stage of anaerobic sludge digestion. The possibility of controlling anaerobic
treatment processes by correcting pH depression using direct current electrolysis was
demonstrated in a previous investigation (3). In order to apply electrolytic pH control on a
plant scale, the proper sizes, types and configurations of electrodes, types of solution
connections and other design parameters must be determined. This investigation was
conducted in order to establish some of the requirements and design parameters needed.
BACKGROUND
In wastewater treatment practice electrodialysis is the only process normally-
considered when electrochemical treatment is mentioned. However, various electrolytic
processes have been used and proposed for wastewater treatment since the year 1889. Miller
and Knipe(4) have summarized the various electrochemical processes which have been used
for wastewater treatment. Most of the electrochemical wastewater treatment processes used
electrolysis to generate chlorine and metal ions in municipal sewage or municipal sewage
mixed with sea water. The chlorine generated at the anode surface would chemically
oxidize materials in the wastewater and kill bacteria. By selecting a suitable anode material
such as iron or aluminum it is possible to generate coagulant ions which would improve
suspended solids removal, form chemical precipitates and provide an intermediate degree
of wastewater treatment.
The concept of using direct current electrolysis to increase the pH of a solution is not
new, but until recently (5) is was never proposed for the anaerobic digestion process. No
mention of pH control by electrolysis could be found in the wastewater treatment literature.
An examination of patent literature did indicate that this type of pH control had been used
or proposed for use in other fields. In 1914, the Berna Milk Company of Thun Switzerland
(6) received a British patent relating to a process for the deacidification of milk by subjecting
it to an electric current. The application for this patent does not indicate the electrochemical
reactions involved. In 1939, Brigs (7) obtained a process patent for varying the pH of sugar
refining juices. Hydrogen evolution at the cathode and chlorine evolution at the anode were
mentioned in the disclosure for this patent. Sandstrom (8) patented a device for changing
the pH of a fermentable liquids. Thompson, et al (9) received a patent for an electrolytic pH
regulator. This apparatus was designed to be used in laboratory experiments involving
microbial cell and tissue culture media. It consisted of an outer platinum electrode which
surrounded an inner electrode of silver. Hydrogen would be generated at the platinum e-
electrode with silver chloride forming at the silver electrode.
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