The significant yield of dissolved oxygen (DO) is one advanced advantage of the electrocatalytic technique for wastewater treatment. Here, we measure DO concentrations during electrocatalytic processing of Taiwanese municipal wastewater and landfill leachate. Chloride ion-containing electrolytes in the wastewater had the most deleterious effect on the production of DO. In contrast, other anions including carbonates, nitrates, sulfates, and phosphates improved DO yield. The Cl- effect can account for electrode erosion, because the anode surface will be impacted by chloride ions. This erosion results in the release of metal ions at the anode that react with DO to form species of metal oxides and deplete the DO in wastewater. However, other cations in the wastewater such as Na+, Ca2+, and Mg2+ are irrelevant with the DO yield in the electrocatalytic system. Results indicate that inert anodes such as dimensionally stable anodes can increase DO concentration, but the metal-related anodes such as stainless steel and TiO2 will decrease DO concentration during the electrocatalytic process in the presence of chloride ions.