Performance of sulfur-based autotrophic denitrification and denitrifiers for wastewater treatment under acidic conditions

Autotrophic denitrification under acidic conditions using sulfide (S²⁻), elemental sulfur (S⁰), and thiosulfate (S₂O₃²⁻) as electron donors are evaluated. Results from batch and column experiments show that when different S species were supplied, different pH conditions and denitrifier communities were required for denitrification to occur. Nitrate and nitrite were removed via autotrophic denitrification at pH ranging from 4 to 8, when S²⁻ or S₂O₃²⁻ was the electron donor, while with S⁰ denitrification was only observed at pH > 6. When S²⁻ was used as electron donor, it was converted to S⁰, and S⁰ was not used while S²⁻ was available. When addition of S²⁻ was discontinued, or S²⁻ depleted, S⁰ that had accumulated was used as electron donor for denitrification. These findings demonstrate that sulfur-based autotrophic denitrification can proceed under acidic conditions, but that the addition of appropriate S species and the presence of an effective denitrifier community are required.