NOVELTY - Coagulation precipitation pretreatment of high-concentration wastewater from a chemical plant is carried out and wastewater is mixed with low-concentration wastewater. The mixed wastewater is supplied to a stage (I) aerobic system and stage (II) aerobic system in turns after treatment in a two-phase anaerobic reactor. The wastewater is then supplied to a Kieselguhr disposing tank for clarification and filtration to reach discharge standards.    USE - Coupling treatment of wastewater from chemical plant e.g. production wastewater of high-boiling solvent, resin wastewater, paint-production wastewater, device-washing water, pump-washing water, domestic wastewater, and early-stage rainfall (all claimed).    ADVANTAGE - The method enables efficient, stable and economical treatment of wastewater, discharging effluent with required discharge standards.    DETAILED DESCRIPTION - Coagulation precipitation pretreatment of high-concentration wastewater from a chemical plant is carried out and wastewater is mixed with low-concentration wastewater. The mixed wastewater is supplied to a stage (I) aerobic system and stage (II) aerobic system in turns after treatment in a two-phase anaerobic reactor. The wastewater is then supplied to a Kieselguhr disposing tank for clarification and filtration to reach discharge standards. High-concentration wastewater has a chemical oxygen demand (COD) of more than 10000 mg/L, and low-concentration wastewater has a COD of less than 1000 mg/L. The mixed wastewater has a COD of 5000-10000 mg/L. The reaction conditions of the two-phase anaerobic reactor include a working temperature of 20-40 degrees C, a total COD volume loading of 4 kg COD/(m3.day), and a pH of produced acid phase of 5-6.5 and that of produced methane phase of 6.5-7.5. The reaction conditions of stage (I) aerobic system operating in high load manner include a sludge load larger than 1 kg COD/kg MLSS.day, where MLSS is more than 5000 mg/L, and dissolved oxygen of 0.5-2 mg/L. The reaction conditions of stage (II) aerobic system operating in low load manner include a sludge load of 0.05-0.2 kg COD/kg MLSS.day with dissolved oxygen of 3-5 mg/L. The stage (II) aerobic system forms a PACT process by adding powered activated carbon at 50-200 mg/L.