Effect of Electrical Current and the External Source of Carbon on the Characteristics of Sludge from the Sequencing Batch Biofilm Reactors

This work presents the results of an experiment on the effect of electrical current density (53, 105, 158 and 210 mA/m(2)), the type of an external source of carbon (citric acid, potassium bicarbonate) and C/N-NO3 ratio (0.5, 1.0 and 1.5) on the quantity and quality of formed sludge. The experiment was conducted in sequencing batch biofilm reactors (SBBRs), under anaerobic conditions, with and without the passage of electrical current, under controlled pH of 7.5- 8.0. The study demonstrated that in the reactors with electrical current passage and external source of carbon, the volume of sludge increased along with the current density increase from 53 to 158 mA/m(2). At its highest density (210 mA/m(2)), the concentration of sludge was insignificantly lower. For all densities of electrical current and C/N-NO3 values, the concentrations of sludge formed in the reactors with potassium bicarbonate (1.00 to 1.26 g d. m./L) were lower than in the reactors with citric acid (1.26 to 1.30 g d. m./L). The concentration of organic matter was higher in the sludge from the reactors with electrical current passage and potassium bicarbonate, compared to the sludge from the reactors with citric acid. In the reactors with electrical current passage and external source of carbon, the total nitrogen content in the sludge decreased along with the C/N-NO3 ratio increase for current densities of 53 and 105 mA/m(2). For a higher electrical current density, the nitrogen content in the sludge was similar. Irrespectively of the current density, the nitrogen content in the sludge from the reactors with citric acid was higher than in the sludge from the reactors with potassium bicarbonate. For higher current densities (158 and 210 mA/m(2)) the increase in the C/N-NO3 value caused an increase in the P content in the sludge. The electrical current density increase contributed to increasing the content of phosphorus in the sludge. The phosphorus content in the sludge from the reactors with citric acid was lower than in the sludge from the reactors with potassium bicarbonate. The CST values prove that the sludge formed during the wastewater treatment in electrobiological SBBR was characterized by very high dewaterability. The capillary suction time decreased along with increasing the electrical current density but was not significantly affected by the type of carbon source.