Secret underneath: Fouling of membrane support layer in anaerobic osmotic membrane bioreactor (AnOMBR)

Anaerobic osmotic membrane bioreactor (AnOMBR) holds promise for simultaneous wastewater purification and biogas production, allowing for an energy and carbon-neutral treatment facility. In a typical AnOMBR, reverse osmosis (RO) is employed for re-concentrating draw solution for continuous operation and cost saving. We compared membrane fouling behaviors between AnOMBR-RO hybrid system and AnOMBR without RO unit. We concluded that the porous support layer was susceptible to both inorganic scaling and biofouling in the closed-loop AnOMBR-RO system. We also explored two cleaning approaches to mitigate inorganic scaling and biofouling. Specifically, ethylenediaminetetraacetic acid (EDTA) was introduced into draw solution for minimizing inorganic scaling, but biofouling was deteriorated as EDTA provided extra nutrients for bacterial proliferation and biofouling. On the other hand, chemical cleaning of membrane support layer was performed using NaClO solution for biofouling control, but such cleaning efficacy attenuated after several cleaning cycles, because inorganic minerals accumulated and grew within membrane porous layer which could not be flushed by NaClO cleaning. Our finding highlighted the complexity and courter intuitive perspective to membrane fouling and cleaning in AnOMBR-RO hybrid system for inorganic scaling and biofouling management.