Abstract: To address unstable ammonia nitrogen treatment efficiency in the actual operation of chemical wastewater treatment plants, causal chain analysis method was applied for in-depth problem diagnosis. On-site investigation, sampling and laboratory testing identified two root causes: one is the inadequate sludge return flow with dead zones in the secondary sedimentation tank, and the other is the insufficient influent alkalinity impairing nitrification function. Meanwhile, to resolve these issues, experiments were conducted to screen alkalinity-adjusting chemicals and optimize their dosage. Recommendations were also proposed for optimizing the operation of the A/O process.

Key words: enhancement of nitrification function, ammonia nitrogen, alkalinity