Activated manganese dioxide can replace the enzyme catalase as catalyst of the hydrogen peroxide decomposition in the steady state peroxide feeding method for K(L)a determination in aeration equipment. The equivalence of both techniques was experimentally demonstrated in deionized water. Manganese dioxide is thus a reliable alternative for the application of the method in media Like strong electrolyte solutions where catalase is quickly deactivated, but some limitations of its own have also to be considered with oxidizable fluids, e.g. polypropylene glycol.