THESIS
2018
xvi, 87 pages : illustrations (some color) ; 30 cm
Abstract
Hydrogen sulfide is formed in the sludge from chemically enhanced primary treatment
(CEPT), and it causes odor nuisance and safety concerns during the sludge holding and
shipping period. In this research study, the efficacy of various approaches for hydrogen
sulfide control were evaluated, including dosing with soluble oxidants, and the
integrated use of soluble oxidants with ferric oxide/biocide/micro-aeration. Among the
approaches tested, dosing with hydrogen peroxide and the combined use of hydrogen
peroxide with micro-aeration are relatively cost-effective, and can reduce the dissolved
sulfide to 0.5 mg/L in the sludge phase, and the hydrogen sulfide to 5 ppm in the
gas phase within 4 hours. Compared to dosing soluble oxidants only (e.g., H
2O
2,
NaClO
2 and ClO
2), the integ...[
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Hydrogen sulfide is formed in the sludge from chemically enhanced primary treatment
(CEPT), and it causes odor nuisance and safety concerns during the sludge holding and
shipping period. In this research study, the efficacy of various approaches for hydrogen
sulfide control were evaluated, including dosing with soluble oxidants, and the
integrated use of soluble oxidants with ferric oxide/biocide/micro-aeration. Among the
approaches tested, dosing with hydrogen peroxide and the combined use of hydrogen
peroxide with micro-aeration are relatively cost-effective, and can reduce the dissolved
sulfide to < 0.5 mg/L in the sludge phase, and the hydrogen sulfide to < 5 ppm in the
gas phase within 4 hours. Compared to dosing soluble oxidants only (e.g., H
2O
2,
NaClO
2 and ClO
2), the integrated use of soluble oxidants with micro-aeration or
biocides can reduce the demand for soluble oxidants, so as to achieve a similar/even
better sulfide removal efficiency. The reaction kinetics of aqueous sulfide oxidation by
the selected oxidants (e.g., H
2O
2, NaClO
2, NaClO, and ClO
2) were investigated and
modelled in synthetic water using a stopped-flow spectrophotometer. The reactions
followed pseudo first-order kinetics, and the second-order rate constants between
sulfide and the selected oxidants were ranked as: ClO
2 > ClO
2- > NaClO >> H
2O
2.
Sulfide was oxidized to elemental sulfur, thiosulfate, sulfate and some unknown sulfur
species through the oxidation by the selected oxidants. The speciation of the sulfur-containing
oxidation products was dependent on the types of oxidants as well as their
dosages. An unexpectedly high sulfide removal efficiency was observed by dosing with
H
2O
2 in the CEPT sludge, and it was verified to be attributed to the interactions between
H
2O
2 and iron species (e.g., FeS) in the CEPT sludge. The iron species activated the
H
2O
2, produced hydroxyl radicals, and together with H
2O
2 itself, contributed to the
sulfide oxidation.
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