Single-stage or two-stages bio-electrochemical treatment process of drainage from soilless tomato cultivation with alternating current

Abstract

This work substantially extends knowledge on the possibilities of treating drainage from full-technical scale soilless tomato cultivation. Experiments were carried out in one stage bio-electrochemical reactor and separate biological and electrochemical reactors connected in series, with using alternating current. The study aimed to determine: the effect of single-stage, two-stages wastewater treatment process and hydraulic retention time (HRT) on the effectiveness of contaminant removal and organic substrate consumption, the contribution of biological and electrochemical processes and on the kinetics of contaminant removal. The use of coupled biological and electrochemical processes in one reactor (R1) showed the highest efficiency nitrogen removal, reaching 62.7 % (HRT = 1d) and 89.8 % (HRT = 7d), respectively. The separation of biological (R2-I) and electrochemical processes (R2-II) demonstrated the first one (R2-I) to be mainly responsible for denitrification (TN removal effectiveness at 51.9 % compared to 54.9 % effectiveness of the whole system). In single R1, the concentration of phosphorus in the effluent reached 2.32 ± 0.47 mg P∙L−1 (97.1 %; HRT = 1d) and 1.16 ± 0.06 mg P∙L−1 (98.3 %; HRT = 7d). In R2 enabled reducing phosphorus concentration in the effluent to 0.18 ± 0.07 mg P∙L−1 (99.8 %). The study showed that using of alternating current proved viable in increasing the rate and effectiveness of denitrification, but only if we apply electric current simultaneously with external source of organic carbon.