Exploring the potential application of hybrid permonosulfate/reactive electrochemical ceramic membrane on treating humic acid-dominant wastewater

Abstract

Discharge of untreated or improperly managed landfill leachate could pose a significant threat on environment due to the high strength of complex inorganic composition and abundant refractory humic acid (HA). This is the first work introducing a promising energy efficient technology using Ti4O7 anode reactive electrochemical membrane (REM) coupled with permonosulfate (PMS) to address HA-enriched wastewater. The removal performance, possible generation of reactive species along with reaction mechanisms in PMS/REM system were proposed and compared with the traditional REM system. Regardless of electrical potential, chlorine concentration, water flux and PMS dosage (with similar ionic strength by adding SO42- for REM alone), the hybrid PMS/REM system prevails the REM system alone in terms of HA degradation and energy efficiency. However, the extent of removal performance is also largely dependent upon specific condition. An increase in PMS dosage and anode electrical potential was beneficial for HA degradation, but addition of chloride imposed adverse effects on HA removal efficiency. Of those parameters, the influence of water flux on HA degradation was trivial. Compared to REM alone, in which HA was mostly removed via electrosorption, PMS/REM system, otherwise, significantly enhanced mineralization of HA. The electron paramagnetic resonance experiments demonstrated the absence of sulfate radical (SO4•-) in the PMS/REM system and implied that the more efficient performance of the hybrid system over the REM system was likely ascribed to the higher yield of hydroxyl radical (•OH). Besides, nonradical oxidation also played an important role in the PMS/REM system with the formation of a transition state of PMS molecule (PMS*), which could facilitate •OH production by inhibiting oxygen evolution site reactions.