Four sequencing batch reactors (SBR) are operated with sludge residence time （SRT）of 2, 8, 14, and 20 days to analyze the impact of SRT on removal of sulfanomide (5 μg/L). In batch experiments, three treatments (active biomass, inhibited biomass, and controls of no biomass) are performed in 100 mL batch reactors in triplicate that simulated one SBR cycle, and are investigated to distinguish biodegradation, biosorption, and volatilization losses, respectively. The results show that biomass removed an average 2.14±0.60 μg/g SS of sulfamethoxazole, 1.14±0.63 μg/g SS of sulfadiazine, 2.33±0.67 μg/g SS of sulfadimethoxine, 2.45±0.85 μg/gSS of sulfamerazine, with 63%, 83%, 35%, 55% of the removal respectively due to sorption. When SBRs (3 L total volume) are spiked continuously with 5 μg/L sulfamethoxazole for 60 days, 10%, 41%, 51%, 58% is removed with SRTs of 2d, 8d, 14d, 20d, respectively. Removal increased significantly with SRT, but the normalized mass removed per gram of biomass decreases. Growth of filamentous organisms with a 2-d SRT increases the sorption capacity of this sludge, although biodegradation is the dominant mechanism for removal. Higher biomass concentrations established by longer SRTs are more significant for biodegradation than species diversity, which do not vary with SRT. As wastewater treatment plants implement longer SRTs for nutrient removal, they will also achieve improved removal of some pharmaceuticals.