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Cause and Remediation of Hydrogen Sulfide Emissions from a Sodium-Based Flue Gas Desulfurization Sludge Disposal Pond

Battelle, Pacific Northwest Laboratories, Interfacial Geochemistry Group, K3-61, P.O. Box 999, Richland, WA 99352.

^* Corresponding author (cc-ainsworth{at}pnl.gov).

ABSTRACT

A flue gas desulfurization (FGD) sludge disposal pond with a history of H₂S emissions to the atmosphere was studied to determine the cause of emissions and remediation strategies. The pond receives sludge and associated waters from a single-pass Na₂CO₃ flue gas scrubber unit. The pond water is a sodic alkaline brine with large SO₃ and S₂O₃ concentrations (>5000 mg L^–1), and hence, an elevated chemical O₂ demand. The pond water H₂S concentrations are small as a result of periodic H₂O₂ additions. The sediments, however, have as much as 3500 mg L^–1 H₂S in the pore water. The production of H₂S appeared to originate from the sediments and diffuses through the anoxic water column with little oxidation. Large concentrations of the reduced sulfur species SO₃ and S₂O₃ were present as a result of the flue gas desulfurization process and incomplete oxidation of H₂S. The pond was reconstructed to circulate the water through an air injection system that was designed to oxidize the SO₃ and S₂O₃ to SO₄, and thereby reduce the chemical O₂ demand. After the installation of the air injection system, emissions of H₂S ceased and the concentrations of SO₃ and S₂O₃ were reduced by at least a factor of 10 within 3 to 4 wk. The production of H₂S in the sediments, however, did not appear to be affected, nor did it appear that it will be reduced in the future by the air injection system.