Removing H2S with Limited Oxygen from Dairy Digesters

Jul 06, 2022

The renewable natural gas (RNG) energy market is growing exponentially in the United States and Canada. As a result, numerous new dairy digesters are being built to extract methane from dairy manure and converting it into usable natural gas. This process helps capture methane from manure before it decomposes naturally and detrimentally enters the atmosphere.

An emerging issue for the developers of diary digester projects is how to remove H2S from the gas stream in a low oxygen environment. Removing H2S is one of the first steps to produce pipeline quality gas from digester gas. In order to meet typical pipeline injection specifications, the H2S must be reduced below 4 ppm, while maintaining an oxygen level at or below 0.2% in the product gas. Most H2S removal medias need oxygen to regenerate the iron component responsible for the removal of H2S. In these scenarios, most iron-based or carbon-based pelletized medias become less efficient due to the lack of sufficient oxygen.

In FerroSorp®, Interra Global’s premier H2S removal media, iron hydroxide is the key ingredient that attracts the H2S. It is then chemically changed into elemental sulfur which attaches to the inside of the FerroSorp® pellets. Iron hydroxide based media natively contains 25% more oxygen per iron atom than traditional iron oxide based medias. This higher oxygen content within the media itself is responsible for effectively removing H2S without needing additional oxygen from the gas stream.

Even with limited oxygen, FerroSorp® still extracts more H2S than other products thanks to the high iron hydroxide content. While other products need oxygen regeneration to be effective, FerroSorp® is only made more effective with oxygen regeneration, promoting three to four times more H2S removal.

Removing oxygen from the product gas downstream adds cost and complexity to the system, so adding oxygen to the biogas to aid in the removal of H2S doesn’t always economically make sense. FerroSorp® saves digester operators valuable time and money with its higher absorption efficiency and extended change-out frequency, even with only trace amounts of oxygen. In addition, FerroSorp® will remove about half the oxygen in the raw biogas stream during the H2S removal process, offering this extra cost-saving benefit down the line.

With iron hydroxide as the base H2S removal ingredient, FerroSorp® is the most competitive H2S removal media available. While oxygen can extend the usable life of FerroSorp® through regeneration, even in limited oxygen applications FerroSorp® still removes enough H2S to make it the most effective solution for the RNG market.

If you wish to discuss how FerroSorp® can work for you, email the Interra Global Sales team at, 847.292.8600, or visit

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