Some competing technologies are:
– Calcium Nitrate – Calcium Nitrate works because the sulfide-producing anaerobic bacteria would prefer to use nitrogen as an energy source than they would sulfur. When there is a lot of nitrogen (or nitrates) in the waste stream, the anaerobic bacteria are content using the nitrate and therefore do not produce any hydrogen sulfide. Calcium nitrate can be very effective in reducing odor and corrosion caused by hydrogen sulfide; however, as you change the food source of the bacteria, it is inevitable that there needs to be more food added to feed this growing population of bacteria, which leads to increased usage over time in order to continue the odor and corrosion control. Additionally, instead of producing hydrogen sulfide as a byproduct, bacteria that feed on nitrates will produce nitrogen as a byproduct. This causes two problems – first, it adds nitrogen to the system and could trigger nitrogen discharge limits at the plant; secondly, this nitrogen will bubble to the surface wherever there is a future pressure drop in the system, causing fats, oils, and greases to float to the top of the waste stream and can cause blockages in the system that will need to be dealt with in some fashion.
– Iron Salts – Iron salts are a common, cost-effective way to bind hydrogen sulfide in waste streams. They are available as ferric chloride, ferrous chloride, ferrous sulfate, etc. These compounds work very well when the pH is alkaline (above pH of 8), but if the pH is lowered at any further point, the hydrogen sulfide can re-volatize. Additionally, iron salts can create films on the walls of pipes and pumps and can cause premature flocculation of solids in the waste stream. In general, large amounts of iron salts need to be added to the system in order to control sulfide, and this generally adds a significant amount of solids that need to be removed in a centrifuge or dewatering press downstream from the sulfide treatment.
– Hydrogen peroxide (standalone) – In some waste streams, hydrogen peroxide (normally 35% or 50%) is used to oxidize hydrogen sulfide. This can be effective, but hydrogen peroxide is a very strong and very versatile compound that will attack almost any oxidizable compound in the waste stream. The result of this versatility is that if your goal is only to remove hydrogen sulfide, you need to add more peroxide than is dictated by the chemical reaction, as much of the peroxide will be “wasted” in the oxidation of other compounds, which may not be problematic to the system. The addition of Ultra-S3 to a system that only uses hydrogen peroxide makes the oxidation of hydrogen sulfide much more efficient, generally saving up to 30-40% on chemical treatment costs.
– Magnesium Hydroxide (“Milk of Magnesia”) – Magnesium Hydroxide is a commonly used technology that looks like a chalky milk. It works by raising the pH of wastewater so that the hydrogen sulfide would prefer to stay in the liquid phase as opposed to the gas phase. When hydrogen sulfide is in the gas phase, it leads to odor and corrosion issues. The downsides of this treatment are that, because of its chalky physical nature, it can clog up the wastewater infrastructure, including pipelines and pumps; additionally, if there is ever a point where more water joins the system, it can cause a quick drop in pH, leading to all of the water phase hydrogen sulfide transitioning to the gas phase, creating a large plume of hydrogen sulfide concentrations in the air. – ProSweet – this is a GE product that is used in industrial applications for H2S treatment. It is a patent protected formula that acts to scavenge or sequester H2S in wastewater. It seems to work well, but in our lab studies, it did not perform as well as Ultra-S3. Ultra-S3 is also a price competitive alternative to this technology.
– Ozone – sometimes you’ll see ozone being used to treat H2S. Ozone is incredibly expensive to run, can be dangerous for people to breathe the ozonated air, and the machines that produce ozone are typically not very reliable.
– Triazene – this is a commonly used technology in the oil field in the amine family. The downsides of this technology are the nitrogen described above. Amine chloride also apparently causes fouling in distillation processes.