Limited Utilization of an External Carbon Source in a Rotating Electro-Biological Disc Contactor (REBDC)

Overdosing an external carbon source can lead to its incomplete utilization. With this in mind, this study aimed to investigate the effect of carbon dosing on nutrient removal in a rotating electro-biological disc contactor (REBDC) treating hydroponic tomato wastewater and to evaluate its impact on effluent COD under a constant electric current (2.5 A/m2). In REBDC, discs served as the cathode, and an aluminum sheet placed in the tank served as the anode. Sodium acetate was added to provide carbon to nitrogen (C/N) ratios of 0.5, 1.0, 2.0, and 3.0. The HRT was 24 h. The phosphorus removal efficiency in the REBDC exceeded 90% at C/N ratios of 0.5, 1.0, and 2.0. A several-fold increase was observed in nitrogen removal efficiency at C/N = 2.0 and C/N = 3.0 compared to C/N = 0.5 (9 and 11 times higher, respectively). At C/N ratios of 2.0 and 3.0, the efficiency was 56.0% and 65%, respectively. Considerable amounts of unutilized organic carbon were found in the REBDC-treated wastewater. The rational solution would be to extend the HRT, which would enable greater substrate consumption and nitrogen removal.