Bioelectrochemical oxidation of organics by alkali-halotolerant anodophilic biofilm under nitrogen-deficient, alkaline and saline conditions

- First study on bioelectro-oxidation of oxalate under alkaline and saline conditions.
- Activated sludge as inoculum and effect of nitrogen supplementation were tested.
- Acetate was required as co-substrate with oxalate for start-up.
- The established bioanodes efficiently converted acetate and formate to current.
- Activated sludge was a poor source of oxalotrophic microorganisms.

This work aimed to study the feasibility of using bioelectrochemical systems (BES) for organics removal under alkaline-saline and nitrogen (N) deficient conditions. Two BES inoculated with activated sludge were examined for organics (oxalate, acetate, formate) oxidation under alkaline-saline (pH 9.5, 25 g/L NaCl) and N deficient conditions. One reactor (R1) received ammonium chloride as an N-source, while the other (R2) without. The reactors were initially loaded with only oxalate (25 mM), but start-up was achieved only when acetate was added as co-substrate (5 mM). Maximum current were R1: 908 A/m3 (organic removal rate (ORR) 4.61 kg COD/m3·d) and R2: 540 A/m3 (ORR 2.06 kg COD/m3·d). Formate was utilised by both anodic biofilms, but the inefficient oxalate removal was likely due to the paucity of microorganisms that catalyse decarboxylation of oxalate into formate. Further development of this promising technology for the treatment of alkaline-saline wastewater is warranted.