CAUSE AND REMEDIATION OF HYDROGEN-SULFIDE EMISSIONS FROM A SODIUM-BASED FLUE-GAS DESULFURIZATION SLUDGE DISPOSAL POND

A flue gas desulfurization (FGD) sludge disposal pond with a history o f H2S emissions to the atmosphere was studied to determine the cause o f emissions and remediation strategies. The pond receives sludge and a ssociated waters from a single-pass Na2CO3 flue gas scrubber unit. The pond water is a sodic alkaline brine with large SO3 and S2O3 concentr ations (>5000 mg L(-1)), and hence, an elevated chemical O-2 demand. T he pond water H2S concentrations are small as a result of periodic H2O 2 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 t he 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 hue gas desulfurization process a nd incomplete oxidation of H2S. The pond was reconstructed to circulat e the water through an air injection system that was designed to oxidi ze the SO3 and S2O3 to SO4, and thereby reduce the chemical O-2 demand . After the installation of the air injection system, emissions of H2S ceased and the concentrations of SO3 and S2O3 were reduced by at leas t a factor of 10 within 3 to 4 wk. The production of H2S in the sedime nts, however, did not appear to be affected, nor did it appear that it will be reduced in the future by the air injection system.