Energy-efficient treatment of organic wastewater streams using a rotatable bioelectrochemical contactor (RBEC)

A membraneless bioelectrochemical system – rotatable bio-electrochemical contactor (RBEC) consists of an array of rotatable electrode disks was developed to convert the chemical energy from wastewater organics (acetate) directly into electricity. Each rotatable electrode disk had an upper-air exposing and a lower-water submerging halves. Intermittent rotation (180°) enabled each halve to alternately serve as anode and cathode. Removal of chemical oxygen demand (COD) was increased by 15% (from 0.79 to 0.91 kg COD m−3 d−1) by allowing electron flow from the lower to the upper disk halves. Coupling with a potentiostat could alleviate cathodic limitation and increased COD removal to 1.32 kg COD m−3 day−1 (HRT 5 h). About 40% of the COD removed was via current, indicating that the biofilm could use the lower half disk as electron acceptor. The RBEC removed COD more energy-efficiently than conventional activated sludge processes as active aeration is not required (0.47 vs. 0.7–2.0 kW h kg COD−1).

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► Rotatable bioelectrochemical contactor (RBEC) as a new BES configuration.
► Rotatable disk divided into a lower anodic and upper cathodic halves.
► Intermittent disk flipping established biofilms at both disk halves and allowed polarity inversion.
► Alternating anodic and cathodic catalysis alleviated the typical pH imbalance limitation.
► RBEC as MFC yielded net electricity but input of extra power further increased current and COD removal.