Carbonized sludge powder as a process-support material for activated sludge treatment of blackwater-dominant domestic wastewater

ABSTRACT

Flow diagram showing conversion of excess sludge into carbonized sludge powder through oxygen-limited carbonization at 600 degree symbol C for 1h. The carbonized sludge powder is then added to activated sludge. The final panel shows the expected effluent response: lower COD, BOD, and TSS, and higher apparent solids retention. A bottom statement notes that CSP may support pollutant removal and apparent solids retention in a laboratory-scale activated sludge system.

This laboratory-scale study evaluated carbonized sludge powder derived from excess sludge as a process-support material for activated sludge treatment of blackwater-dominant domestic wastewater. The material was prepared by drying, sieving, oxygen-limited carbonization in a lidded crucible at 600 °C for 1 h, washing, ultrasonic cleaning, and oven drying. Material properties were characterized by surface-area analysis, scanning electron microscopy, and energy-dispersive X-ray fluorescence. Carbonization increased the surface area from 12.244 to 49.447 m2/g and the total pore volume from 0.0599 to 0.1230 cm3/g while retaining a mineral-rich composition dominated by Fe2O3, SiO2, and CaO. A 9-day sequencing batch reactor screening showed broadly similar chemical oxygen demand and total suspended solids removals across the tested dosages, whereas mixed-liquor solids increased at higher dosages; therefore, 0.05 g L−1 d−1 was selected for continuous-flow operation. During steady-state operation, carbonized sludge powder addition was associated with lower effluent chemical oxygen demand, biochemical oxygen demand, and total suspended solids than the control reactor. However, the absolute biochemical oxygen demand reduction was modest. The material also increased mixed-liquor solids, apparent solids retention time, settled sludge volume, and sludge volume index. Further work is required to evaluate cost, energy demand, environmental safety, and full-scale applicability.