Abstract

The purpose of this research was to study the impact of direct current (DC) application on activated sludge (AS) properties. A control reactor without an electrical field and a series of 1.5L batch reactors were filled with activated sludge at two levels of mixed liquor suspended solid concentrations (LR MLSS: 5000-7000 mg/L and HR MLSS: 10000-12000 mg/L) and were subjected to four electrical modes (continuous, 5ON:5OFF, 5ON:10OFF and 5ON:15OFF) for 48 hours. Experiments were performed for both AS alone and AS mixed with different concentrations of calcium salt (250 and 750 mg/L). The sludge volume index (SVI), time to filtration (TTF), particle sizes, specific oxygen consumption rate, soluble microbial products (SMP) and phosphate concentrations were measured before and after the experiments. Designed reactors’ parameters permitted the microorganisms to preserve their bioactivity. Results showed that the continuous electrical mode achieved the highest reduction in SVI. At all electrical modes, over 75% reduction in phosphate concentration was achieved. For most of the AS properties, the impact of EC at LR MLSS was higher than that at HR MLSS. A longer exposure time to DC resulted in smaller particle sizes. As the exposure time to DC decreased, the amount of SMP deposited on the anode surface increased. More calcium was deposited on the cathode surface at a longer exposure time. Furthermore, the addition of 250 mg Ca2+/L to AS, in the absence of an electrical field, resulted in 33% and 63 % higher SMP and phosphate removal efficiency. The results can be applied to better control electrocoagulation processes within various wastewater treatment system including MBR and SMEBR.