Remediation of Sulfides in Produced Waters of the Oil and Gas Industry Using Hydrogen Peroxide.

Produced waters are often treated in open lagoons where hydrogen sulfide (H₂S) can off gas, posing a risk to human health and the environment. The aim of this study was to optimize a treatment process using hydrogen peroxide (H₂O₂) to oxidize H₂S while minimizing off gassing. Samples of produced water from West Texas and laboratory-prepared waters utilizing sodium sulfide (Na₂S) or biogenic polysulfides were oxidized with H₂O₂ alone or in combination with copper or iron catalysts, sodium hydroxide (NaOH), or a commercial sulfide oxidizer, HydroPower Green™. Sulfur speciation was measured using Hach test kits for sulfide/sulfate/sulfite and Dräger tubes for headspace H₂S. HydroPower Green™ (HPG) helped to reduce H₂S in the headspace of water samples; some of this was pH related as NaOH also worked, but not as well as HPG. The dose of peroxide necessary to oxidize sulfides to sulfate is a function of the oxidation-reduction potential (Eh) of the water and total sulfide concentration as well as pH; approximately a 1–4:1 ratio of peroxide to sulfide concentration was needed to oxidize sulfidic waters of pH 7–10 with half-lives under 30 min. Both copper and iron catalysts reduce H₂O₂ demand and the half-life of H₂S. Peracetic acid (PAA) and copper (II) sulfate pentahydrate (CuSO₄, 5H₂O) were explored as biocides for controlling sulfate-reducing bacteria (SRBs) that produce H₂S. An AquaSnap (Hygenia) test kit was employed to monitor relative microbial activity in a wetland porewater containing H₂S. Microbial regrowth occurred after a few days using the highest dose of PAA; these results showed that PAA was being used by bacteria as a carbon source even after the initial substantial reduction in the microbial activity. CuSO₄, 5H₂O at a dose of 1 ppm prevented microbial regrowth. The recommended treatment process from this research is determined by jar testing with H₂O₂, a base for pH control, a biocide, and possibly a metal catalyst or other co-oxidants in order to achieve oxidation of sulfides without H₂S release or the precipitation of metal carbonates or oxides. [ABSTRACT FROM AUTHOR]