Powdered activated carbon promotes sludge granulation and pollutant removal during the treatment of low-carbon-to-nitrogen ratio petrochemical wastewater

Aerobic granular sludge (AGS) slowly forms granules during the treatment of low-carbon/nitrogen ratio (low C/N ratio) petrochemical wastewater. This study investigated adding powdered activated carbon (PAC) to improve granulation during the treatment of low C/N ratio petrochemical wastewater. The optimal dosage for practical applications was also investigated. First, the activated sludge system (R1), a system with added PAC (R2), and a system with added Fe²⁺ (R3) were investigated. The results showed that by day 60, R2 had achieved complete granulation, while R1 and R3 had not. The control group without PAC (R1) and the groups supplemented with PAC (R2, R3, R4, and R5, with 0.5, 1, 2, and 3 g/L PAC, respectively) were studied. The results showed that on day 16, the average particle size of the groups with PAC exceeded 200 μm, while the group without PAC was only 99.9 μm. Moreover, R5 produced the largest particles and achieved COD and NH₄⁺-N removal efficiencies of 86.6% and 98%, respectively. This study provides a practical reference for the application of PAC for treating low C/N ratio petrochemical wastewater.