A pilot-scale system integrating internal circulation and partial nitritation-anammox successfully treated real high-strength membrane-manufacturing wastewater in this study. With this pilot-scale system, a high chemical oxygen demand (COD) removal efficiency of 85 % and a nitrogen removal of 90 % are achieved at an organic loading rate of 6.0 kg COD/m/d. The nitrogenous organic matters in the internal circulation zone are degraded into ammonia nitrogen. In the partial nitrification zone, nitrite accumulation is achieved, providing a suitable NH-N/NO-N ratio for anammox reaction. Partial nitritation is achieved by maintaining an operational temperature at 30–35 °C, free ammonia concentration at 5–7 mg/L and dissolved oxygen at 0.4–0.7 mg/L with a reflux ratio of 150 %. The COD to nitrogen ratio in the internal circulation effluent is maintained below 3.0 to inhibit nitrite oxidizing bacteria. This study demonstrates that a pilot-scale system can efficiently remove organic matters and nitrogen from wastewater of membrane-manufacturing industry.