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Abstract
Electro-dewatering (EDW) of sewage sludge was conducted to investigate the effect of pulsed voltage on EDW performance by comparing it with constant voltage. A pulsed voltage with constant amplitude of 50 V was applied on top of different base voltages (10, 20, or 30 V). The frequency of pulsed voltage was set at 10 Hz to investigate the effect of duty cycle (2%, 5%, 10%, and 20%) on the EDW performance. The results showed that, under the same average voltage, the water content of the dewatered sludge was 0.63% to 4.03% lower under pulse voltage conditions compared to constant voltage conditions, indicating that pulse voltage could enhance EDW performance. Transmission electron microscopy analysis of sludge cells revealed that pulsed voltage was more effective in breaking sludge cells than constant voltage. This resulted in increased release of bound water and a reduction in sludge cake resistance, which is a key reason why pulsed voltage outperforms constant voltage in EDW. The energy consumption of EDW ranged from 0.088 kW·h to 0.381 kW·h per kilogram of removed water. The energy consumption for pulsed voltage at the base voltage of 30 V was about 2%–7% lower than that of constant voltage, while the energy consumption under the lower base voltage (10 V and 20 V) was almost equal to that of constant voltage conditions. Considering both energy consumption and EDW performance, the optimal duty cycle was 5% for a base voltage of 10 V, and 2% for base voltages of 20 V and 30 V. These findings laid theoretical foundation for future application of EDW with pulse voltage.
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