Sulfur dioxide has been shown to be an effective wastewater disinfectant. The aqueous sulfur dioxide creates and oxygen demand in the effulent which must be removed prior to discharge. Oxidation to sulfate is one means of accomplishing this task. Experiments were carried out to determine the effectiveness of transition metals and activated carbon as catalysts for the oxidation of S+IV species in wastewater. Both the metals and carbon are known catalysis, but what inhibitory effect the wastewater might have was unknown. Effectiveness was defined as a combination of catalyst life, effluent quality, and cost. Tradition metals were eliminated as potential catalysts due to the high metal concentrations found in the effluent. The acidic nature of 500 mg/l SO2 dissolved in wastewater (pH 2.5) would dissolve the metals or cause them to desorb from a carbon base. Using downflow contractors, activated carbon was shown to catalyze the reaction as long as sufficient oxygen was available. At a loading rate of 5.5 h carbon/1 and a hydraulic loading of 38 M^3/M^2 * day, 24 hour runs were accomplished without SO2 breakthrough (less than 4 mg/1). Longer runs resulted in gradual breakthrough (40 mg SO2/1 after 96 hours). The cause of the failure was assumed to be the self-poisoning of the catalyst by sulfuric acid (the product of SO2 oxidation) and/or the reduced solubility of oxygen in the sulfuric acid solution. Carbon regeneration, as a catalyst, was accomplished by backwashing the column with tap water. The cost of sulfur dioxide disinfection ranged from $0.23 - $0.73/1000 gallons treated. In general, this process was much more costly than other disinfection systems.
Upton, Ernest J. and Adams, V. Dean, "Catalytic Oxidation of Sulfur
Dioxide in Wastewater" (1982). Reports. Paper 49.