Hydrogen sulfide control in sludge from chemically enhanced primary treatment (CEPT) by chemical dosing and other strategies

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., H₂O₂, NaClO₂ and ClO₂), 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., H₂O₂, NaClO₂, NaClO, and ClO₂) 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: ClO₂ > ClO₂^- > NaClO >> H₂O₂. 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 H₂O₂ in the CEPT sludge, and it was verified to be attributed to the interactions between H₂O₂ and iron species (e.g., FeS) in the CEPT sludge. The iron species activated the H₂O₂, produced hydroxyl radicals, and together with H₂O₂ itself, contributed to the sulfide oxidation.

Date of Award	2018
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology