Hydrogen sulfide is a problematic pollutant in aqueous/sediment systems. This thesis work explored a sulfur-iron redox cycle over iron-based granules for biotic and abiotic hydrogen sulfide control in lab-scale experiments. Dissolved hydrogen sulfide was removed by iron granules including granular ferric hydroxide (GFH), granular ferric oxide (GFO) and rusted waste iron crusts (RWIC), via the abiotic oxidation to elemental sulfur (S(0)) with concurrent reduction of solid Fe(III) to surface-associated Fe(II) and precipitation as iron sulfide (FeS_(s)) by the released Fe²⁺. The control of hydrogen sulfide generated by sulfate-reducing bacteria (SRB) was also achieved through reducing sulfide production by microbial iron reduction that consumed the limited organics and released Fe...[ Read more ]

Hydrogen sulfide is a problematic pollutant in aqueous/sediment systems. This thesis work explored a sulfur-iron redox cycle over iron-based granules for biotic and abiotic hydrogen sulfide control in lab-scale experiments. Dissolved hydrogen sulfide was removed by iron granules including granular ferric hydroxide (GFH), granular ferric oxide (GFO) and rusted waste iron crusts (RWIC), via the abiotic oxidation to elemental sulfur (S(0)) with concurrent reduction of solid Fe(III) to surface-associated Fe(II) and precipitation as iron sulfide (FeS_(s)) by the released Fe²⁺. The control of hydrogen sulfide generated by sulfate-reducing bacteria (SRB) was also achieved through reducing sulfide production by microbial iron reduction that consumed the limited organics and released Fe²⁺. Compared to the abiotic sulfide oxidation, the microbial iron reduction generated more Fe²⁺ to form FeS_(s) but not S(0). GFH and RWIC released more Fe²⁺ than GFO did, leading to their superior efficiencies in the control of biogenic hydrogen sulfide. A portion of solid products (S(0), FeS_(s) and surface-associated Fe(II)) gradually accumulated on the granule surface and caused the iron granules' exhaustion.

The exhausted iron granules were regenerated by mixing with water containing dissolved oxygen (DO), which simultaneously oxidized Fe(II) to amorphous ferric hydroxides and solid sulfide to S(0). The mixing also reduced the granule sizes. The partial S(0) transfer from the granule surface into the bulk solution during the regeneration reduced the S(0) accumulation on the granule surface. These sulfur and iron transformation and phase transfer enhanced the sulfide removal efficiencies of the iron granules during their repeated use-regeneration cycles. The feasibility of iron granule regeneration by dam break flushing in tide-impacted box culverts was demonstrated. The simulated dam break flushing suspended and mixed the iron-laden sediments with the DO-containing water above and oxygenated the sediment pore water, leading to the partial oxidation and regeneration of the used iron granules.