Remedying acidification and deterioration of aerobic post-treatment of digested effluent by using zero-valent iron

This study presents a novel strategy for remedying acidification and improving the removal efficiency of pollutants from digested effluent by using Zero-Valent Iron (iron scraps) in a sequencing batch reactor. Through this strategy, the pH increased from 5.7 (mixed liquid in the reactor without added ZVI) to 7.8 (reactors with added ZVI) because of Fe⁰ oxidation and NO₃^- reduction. The removal efficiencies of COD increased from 11.5% to 77.5% because of oxidation of ferric ion and OH produced in chemical reactions of ZVI with oxygen and because of flocculation of iron ions. The removal efficiencies of total nitrogen rose from 1.83% to 93.3% probably because of autotrophic denitrification using electron donors produced by the corrosion of iron, as well as the favorable conditions for anammox due to iron ions. Total phosphorus increased from -25.8% to 77.1% because of the increase in pH and the precipitation with iron ions.