Mitigating salt accumulation in osmotic membrane bioreactors using ion-exchange resins

Osmotic membrane bioreactor (OMBR) is an emerging technology with great potentials for wastewater treatment and resource utilization. Nevertheless, salinity build-up is still one of main obstacles of OMBR development. In this paper, an OMBR system was combined with a membrane distillation (MD) system to recycle wastewater and an IERs-OMBR-MD hybrid system was developed to mitigate the salt accumulation in bioreactors. Water flux, water quality, properties of activated sludge and membrane fouling were investigated. The results show that the ion-exchange resins (IERs) dosage of 8 g/L can keep a conductivity of 6.87 mS/cm in the bioreactor during 30 d of operation, which was 30% lower than the conductivity in a traditional osmotic membrane bioreactor-membrane distillation (OMBR-MD) without adding the IERs. A water flux difference of about 58% was found between the OMBR-MD system (1.135 L/(m(2) h)) and the IERs-OMBR-MD system (2.675 L/(m(2) h)) after 30 d of operation. The IERs-OMBR-MD produced significantly less fouling to the forward osmosis membrane than the traditional OMBR-MD. We suggest that IERs can be used to absorb soluble salts to mitigate salinity build-up in OMBRs operation. Overall, the IERs-OMBR-MD hybrid system has the potential to recycle wastewater. However, it is necessary to further improve the long-term stability of activated sludge in OMBRs.