NOVELTY - Low concentration ammonia nitrogen wastewater is treated by inoculating anaerobic bacteria-containing sludge in anaerobic reactor; introducing weak alkaline ammonia nitrogen wastewater with concentration of ammonia nitrogen and nitrite nitrogen of 10-20 mg/L to the reactor; controlling the reaction temperature at 25-30 degrees C; discharging the treated wastewater; discharging gas from exhaust opening till the oxidizing bacteria in the reactor becomes dominant microflora. When removal rate of ammonia nitrogen and nitrite nitrogen both reaches 80%, it means the reactor is successfully started.    USE - Method for treating low concentration ammonia nitrogen wastewater (claimed).    DETAILED DESCRIPTION - Treatment of low concentration ammonia nitrogen wastewater comprises:    (A) inoculating anaerobic bacteria-containing sludge in an anaerobic traverse baffle reactor under anaerobic condition; introducing weak alkaline ammonia nitrogen wastewater with concentration of ammonia nitrogen and nitrite nitrogen of 10-20 mg/L and pH value of 7.8-8.3 to the reactor through inflow storage bottle, where constant flow peristaltic pump between the inflow storage bottle and reactor controls water flow so as to control water power detention time to be 24-48 hours; controlling the reaction temperature at 25-30 degrees C; discharging the treated wastewater from the water outlet; and discharging the gas from the exhaust opening till the anaerobic ammonia-oxidizing bacteria in the reactor becomes dominant microflora, lasting for 5 days, and when removal rate of ammonia nitrogen and nitrite nitrogen both reaches 80%, it means the reactor is successfully started; and    (B) introducing ammonia nitrogen wastewater with concentration of ammonia nitrogen and nitrite nitrogen of 20-50 mg/L and pH of 7.8-8.3 to the reactor through inflow storage bottle, controlling water power detention time at 12-48 hours, controlling reaction temperature at 20-30 degrees C, discharging the treated wastewater from the water outlet, and discharging the biogas from the exhaust opening.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic sectional view of the system used for treatment of low concentration ammonia nitrogen wastewater.