H2S in water is a problem that is common to municipal utility systems and oil & gas production. Treatment options include amine sweeteners, aeration (gas stripping), oxidation, membrane treatment, microbiological filtration and/or ion exchange. Aeration and oxidation have recently emerged as common methods for treatment of produced water and flowback - each has its unique challenges.
Historically, aeration has been most commonly applied using either tray, packed tower, diffused air or spray-nozzle methods. However, the equilibrium of sulfide species in water (between H2S and HS-) is highly dependent upon pH. As such, water must normally be treated with acid to lower the pH in order to increase the amount of H2S available for gas stripping. Stripping gas can be either incinerated or re-processed within the sour gas recovery stream to recover valuable energy content.
Encana's award-winning d-70-K Debolt Water Treatment Plant utilizes a 5-stage aeration scheme employed HCl injection, inlet separator, stripping tower, degassing tank and scavenger polish (acrolein). The end-product is suitable for hydraulic fracturing reuse: the acrolein scavenger creates a soluble, irreversible liquid product with non-detectable levels of H2S.
More recently, producers have utilized oxidizers to handle flowback and produced water associated with tight oil and gas fracturing and production. In particular, service providers have developed ozone, chlorine dioxide and hydrogen peroxide systems for deployment in the Marcellus and Eagleford plays. Media-based solutions (potassium permanganate, filtration or ion exchange) are more susceptible to fouling, particularly when the sulfide species are "oil-wet" and require a more aggressive oxidizer to "break through" the hydrocarbon barrier.
Oxidizer-based systems require careful consideration of oxidizer supply-chain logistics, operational simplicity, energy-efficiency and OH&S needs of the end-user. We are currently working on new applications for both aeration and oxidizer solutions with an focus on driving down the overall cost of service to achieve a better balance between CAPEX, OPEX and environmental footprint.