Semi-continuous measurement of oxygen demand in wastewater using biofilm-capacitance

Bio-capacitive coulombs were tested for determination of the 5-day biochemical oxygen demand (BOD5) using a dual-chamber microbial electrochemical cell (MxC) operated at charging (open circuit) and discharging (close circuit) conditions. For acetate medium, the cumulative coulombs charged in a capacitive biofilm anode (open circuit) were well correlated with BOD concentrations (R2 ~ 0.9). The maximum detectable BOD5 concentration with the bio-capacitance MxC was close to 250 mg/L, and the cumulative coulombs were saturated for above the maximum BOD5 concentration (Monod pattern). The bio-capacitance MxC sensor consistently showed high linearity between the cumulative coulombs and BOD5 concentrations for domestic wastewater influent (R2 = 0.93-0.99), despite of 1 min charging. High correlation between the coulombs and BOD5 concentration was also obtained for wastewater effluent at 1 min charging, which indicates that the bio-capacitance MxC sensor can semi-continuously measure BOD5 concentration in wastewater at every 2 min (1 min charging and 1 min discharging).