Sodium metabisulfite is a reducing agent that mainly treats chromium containing wastewater in wastewater treatment. The main pollutant in chromium containing wastewater is hexavalent chromium ions, which mainly come from industries such as processing, electroplating, printing, textile, metallurgy, leather, chemical industry, etc. of chromium containing ores. Hexavalent chromium poses significant environmental hazards, and according to national standards, it must be treated separately and cannot be discharged into a comprehensive pool. Additionally, the concentration of hexavalent chromium must not exceed 0.1.