Toward a method for measuring oxygen transfer in biofilters

The goal of the work presented was partly to identify conditions for adapting to biofilters the "standard" methods used to measure oxygen transfer in clean water, and partly to determine whether or not the addition of cobalt could be avoided to reduce the rate of sulphite oxidation. The following three methods of measurement were implemented in clear water and compared on a bubble column fermenter and a biofilter pilot unit: non-steady state clean water test, off-gas procedure, sulphite determination method. Tests conducted at different air flow rates in the presence of a high concentration of sodium sulphite (2000 mg L-1) demonstrated that the addition of cobalt imposed a significant acceleration factor. In a diphasic environment, the off-gas procedure (with or without cobalt) produces results that are comparable to those associated with the reference method (reoxygenation with cobalt). Under experimental conditions, the sulphite determination method gives results that are below estimates. In the biofilter pilot unit, the method that is best suited to estimating overall oxygenation efficiency in clear water is the off-gas procedure without the addition of cobalt.