84 / 2021-06-30 19:55:17

Effects of anodic and cathodic voltages on development and fouling characteristics of dynamic membrane

Dynamic membrane,Electric field,Electrochemical reaction,External voltage,Fouling control

In a dynamic membrane bioreactor, development of a dynamic membrane (DM), a sludge cake layer formed on a coarse support material, is a key to the separation and retention of solids within the reactor. At the same time, a too thick DM layer leads to a high filtration resistance. Sludge flocs have negative surface charge, and DM growth may be accelerated or delayed using electrostatic attraction or repulsion. In order to explore this possibility, we examined the effects of anodic and cathodic voltages on the development and fouling characteristics of DM during the filtration experiments with anaerobic sludge. Thirteen voltage conditions were tested in quadruplicate: –1.2 to +1.2 V between the DM support layer (stainless-steel mesh) and the counter electrode (stainless-steel mesh) with 0.2 V intervals. The filtration experiments were conducted under submerged conditions in reactors filled with anaerobic sludge (7.5 g suspended solids/L) at a fixed flux of 60 L/m2/h. The DM layers applied with anodic and cathodic voltages showed very different development profiles. The time taken to reach a transmembrane pressure of 400 mbar (T400) increased significantly compared to the control (0 V) when –0.6 V or greater cathodic voltages were applied, with the largest delay (23%) being recorded at −1.0 V, which can be attributed to electrostatic repulsion and possibly electrochemical generation of H2 and/or H2O2. Meanwhile, T400 decreased significantly at +0.2–0.6 V mainly by electrostatic attraction, and the greatest acceleration (8.6%) was observed at +0.4 V, except +1.2 V at which chemical fouling probably due to the formation iron oxides occurred. At +0.8 V or higher anodic voltages, electrochemical generation of O2 and/or reactive oxygen species appears to have impeded DM growth. In addition, the external voltage application significantly affected the cell viability (i.e., live/dead cell ratio) and sludge morphology of the DM layer.