EFFICIENCY OF ELECTROCHEMICAL OXIDATION OF SULFITE AND
OXYGENATION OF WATER
Marvin P. Steinberg, Professor
Department of Food Science
Thomas J. Brumm, Research Associate
Donald L. Day, Professor
Agricultural Engineering Department
University of Illinois
Urbana, Illinois 61801
INTRODUCTION
Aerobic treatment of livestock wastes can result in pollution control for both odors and pathogens
[1]. Aerobic microbial conversion can give a 90% decrease in biochemical oxygen demand and a 65%
reduction in total solids [2,3]. Also, production of single-cell protein, i.e., microbial solids, has been
shown to be valuable as an amino-acid supplement to livestock rations [4,5,6]. The major disadvantage of aerobic treatment is the high energy and maintenance costs of mechanical aerators [7].
An alternative to mechanical aeration is electrolysis of water to produce oxygen and hydrogen.
The commercial process is well known [8]; however, this uses a concentrated KOH solution and the
electrodes are separated by a diaphragm. In case of livestock wastes we studied the in situ electrolysis
of liquid manure by low-voltage DC electricity without a diaphragm [9]. Oxygen is used by the microbial population for aerobic respiration, while the hydrogen, being relatively insoluble in water, is
released and collected as a valuable by-product. Effluent can be used as livestock feed.
Testing of the overall method with wastes has been reported [9,10,11]. This paper reports testing
oxygenation efficiencies of the electrochemical cell using a sulfite solution to deoxygenate water so
that it could be reoxygenated using the electrochemical cell.
OBJECTIVES
The objectives of this study were to determine the effectiveness of a sandwich electrode design
of an electrochemical cell and to study the effects of temperature and voltage on oxidation and
oxygenation rates, current efficiency and power consumption.
PROCEDURE
the sulfite oxidation test commonly used to evaluate mechanical aerators was applied here [12].
A known amount of sodium sulfite (Na.SO,) was added to a solution of 0.1 M sodium sulfate (Na2S04)
in the electrolysis cell. Sulfite acts as a de-oxygenator (Na2SO, + Vi 02 = Na2S014). Addition of an
exact amount of sulfite exerted a known oxygen demand, thereby acting as a chemical simulation of
a microbial oxygen demand. Voltage was applied to produce oxygen at the anode. Dissolved oxygen
(DO) was measured as a function of time with a YSI model 54ABP DO meter. Temperature control
was provided by a water bath.
The anode material was a ruthenium oxide coated titanium (Dimensionally Stable Anode, Electrode Div., Diamond Shamrock Corp., Chardon, OH), and the cathode was stainless steel. Two
anodes and three cathodes, each 76 x 125 mm, were placed in a Plexiglas frame in a sandwich
configuration of alternating cathodes and anodes. Spacing between electrodes was 5 mm. The ratio
of anode surface to reactor volume was 0.42 cmVcm'. The stirred reactor vessels were constructed
of Plexiglas. The hydraulic volume was 0.90 1.
The results of a typical test are shown in Figure I. Upon the addition of sulfite (part A of the
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