Effect of DC electric fields on COD in aerobic mixed sludge processes

This study evaluates the impact of direct electric currents on the physicochemical and biochemical properties of a mixed aerobic culture. First, changes in dissolved oxygen (DO) concentration, pH, electrical conductivity, temperature, and gas production were evaluated for 2 liters of mixed and aerated tap water samples under 13 and 70 mA constant direct currents. Samples (1.5 liters) of acclimated cultures were then placed in bioelectrochemical reactors and exposed to direct electric (DC) fields of 0, 0.28, 0.57, and 1.14 V/cm for a period of 50 h or higher. Dissolved oxygen concentration, pH, electrical conductivity, and temperature were monitored during exposure to electricity. The results showed that direct electric currents did not cause any significant change in the DO and pH of a completely mixed and aerated system of tap water or activated sludge. COD was monitored to assess if applied DC fields inhibited or stimulated COD removal in an aerobic culture. Low level fields of 0.28 V/cm did not have a significant impact on COD reduction. Exposure to higher level DC fields of 0.57 and 1.14 V/cm increased COD reduction. At the highest voltage applied (1.14 V/cm), the rate of COD reduction decreased after the first 24 h of exposure. There appears to be an optimum range, between 0.28 and 1.14 V/cm, where COD reduction in aerobic cultures can be enhanced. The impact of an applied DC field below 0.28 V/cm may be insignificant. A DC electric field greater than 1.4 V/cm may be harmful.