Cake permeability can thus be affected by the composition of oxides. In/during the oxidation of Fe and Mn, a bulk/prevalence of Fe–Mn oxides can easily be formed in the presence of Mn oxides [14]. As a result, the surface roughness of cake layers formed by Fe and Fe–Mn oxides differs, resulting in varied cake permeability. To verify this, the contact angle of the cake surface on a fouled membrane was determined.