Bioelectrochemically-assisted mitigation of salinity buildup and recovery of reverse-fluxed draw solute in an osmotic membrane bioreactor

Abstract

A key challenge for osmotic membrane bioreactors (OMBRs) application is reverse solute flux and consequent salt accumulation in the feed side. Herein, a bioelectrochemical system (BES) was employed to drive reverse-fluxed solutes from the feed of an OMBR into a cathode compartment for recovery and subsequent reuse as a draw solute (DS). Compared to an OMBR without BES function, the present OMBR system enhanced water recovery from 925 to 1688 mL and increased the chemical oxygen demand (COD) removal efficiency from 40.2 ± 8.1 to 75.2 ± 3.3%, benefited from its lower anolyte conductivity of 9.0 mS cm−1 than that of the control system (24.1 mS cm−1). The CO2 addition significantly improved the ammonia recovery rate to 93.3–116.7 g N m−3 h−1 (or 248.0–307.4 g N m−2 d−1), 12.1–14.5 times higher than that without CO2 addition. The recovered DS was successfully applied to accomplish water extraction in the reuse test, and such a recovery/reuse process could result in a normalized water recovery of 3870 mL mol DS−1 or a DS usage of 0.26 mol L−1 (of the recovered water). The energy consumption of the system might be compensated by the production of bioenergy, and the net specific energy consumption was estimated to be 0.004–0.112 kWh m−3 wastewater, 0.007–0.179 kWh kg−1 removed COD, or 0.001–0.020 kWh kg−1 recovered NH4+-N. Those results have demonstrated that bioelectrochemical processes can be an effective approach for in situ mitigation of reverse-fluxed solute in OMBR and recovering “the lost DS” towards both reuse and reduced operational expense.