Electrochemically activated peroxymonosulfate (PMS) pretreatment for fouling remediation during membrane distillation of surface water: Role of PMS concentration and dosing mode

Abstract

Membrane distillation (MD) provides a potential method to supply large volumes of good quality potable water from surface water resources, avoiding the risk of long-term water shortages. However, the high abundance of dissolved natural organic matter (DOM) in surface water induces severe membrane fouling, which reduces productivity and increases energy consumption. Therefore, for the first time, electrochemically activated peroxymonosulfate (PMS) treatment was applied prior to the direct contact (DC)-MD process with the aim of reducing the deposition of organics and inorganics on the membrane and reducing membrane fouling. Results showed that supplying PMS continuously at a rate of 0.10 mM/min, eliminated 30.4% of dissolved organic carbon (DOC). Furthermore, fluorescence parallel factor (PARAFAC) analysis showed that >60% of two fluorescent substances were removed after 60 min of the electrochemically activated PMS pretreatment at a current density of 5 mA/cm2. Electrochemical activation of PMS generated •OH directly, facilitating the removal and degradation of DOM. In terms of the DCMD performance, almost no normalized flux decline was observed for the DCMS process after 0.01 mM/min pre-oxidation, while 44.8% flux decay occurred in the standalone DCMD treating raw surface water. Compared with continuous dosing, the use of a one-time dosing mode achieved a better outcome, as more small organic molecules generated in continuous dosing mode are not conducive to membrane fouling control. Therefore, electrochemically activated PMS could be an effective tool to mitigate membrane fouling in MD processes, although the characteristics of membrane and feed should be considered.