Effect of nitrate concentration, pH, and hydraulic retention time on autotrophic denitrification efficiency with Fe(II) and Mn(II) as electron donors

The role of electron donors (Fe²⁺ and Mn²⁺) in the autotrophic denitrification of contaminated groundwater by bacterial strain SY6 was characterized based on empirical laboratory-scale analysis. Strain SY6 can utilize Fe²⁺ more efficiently than Mn²⁺ as an electron donor. This study has shown that the highest nitrate removal ratio, observed with Fe²⁺ as the electron donor, was approximately 88.89%. An immobilized biological filter reactor was tested by using three levels of influent nitrate (10, 30, and 50 mg/L), three pH levels (6, 7, and 8), and three levels of hydraulic retention time (HRT; 6, 8, and 12 h), respectively. An optimal nitrate removal ratio of about 95% was achieved at pH 6.0 using a nitrate concentration of 50 mg/L and HRT of 12 h with Fe²⁺ as an electron donor. The study showed that 90% of Fe²⁺ and 75.52% removal of Mn²⁺ were achieved at pH 8.0 with a nitrate concentration of 50 mg/L and a HRT of 12 h. Removal ratio of Fe²⁺ and Mn²⁺ is higher with higher influent nitrate and HRT. A weakly alkaline environment assisted the removal of Fe²⁺ and Mn²⁺.