Managing hydrogen sulfide in a wastewater collection system is important not only for mitigating odor but also for preventing corrosion and ensuring the optimum performance of the system. We spoke with Jennifer Miller of Evoqua Water Technologies to understand the impacts of hydrogen sulfide and how to prevent them.
WATERWORLD: What is hydrogen sulfide and how does it cause corrosion?
JENNIFER MILLER: Hydrogen sulfide is a naturally occurring compound in wastewater conveyance or collection systems. Under acidic or turbulent conditions in the collection system, hydrogen sulfide is released from the wastewater in the form of a gas. Thiobacillus bacteria that are present in the wastewater system oxidize, or react with, the hydrogen sulfide gas to form sulfuric acid. The resulting sulfuric acid corrodes sewer pipes and weakens concrete structures, and shortens the life of the collection system, setting the stage for dangerous sewer collapses.
WW: What effect does this have on the collection system?
JM: When left untreated, the sulfuric acid can break down reactive surfaces in the infrastructure, shortening the life of the wastewater treatment system. This potentially creates an environment where sewer collapses can occur. Another effect is the high cost to state and local government agencies and emergency services who have to respond to those repairs. If there’s damages to the infrastructure, and potentially accidents that can occur with things like road collapses, this causes negative public exposure for the plant. Something that is often overlooked are the serious health risks to plant employees and the community from the hydrogen sulfide gas that is released to the atmosphere. There was a report prepared by the US EPA, and submitted to Congress, which estimated that the annual rehabilitation cost of sewer rehabilitation was about $6 billion (1991 dollars). Within the report they found that over 80% of sewer collapses were due to hydrogen sulfide induced corrosion.
WW: How can a utility prevent or treat corrosion?
JM: Since sewer systems are essentially underground, it can be difficult to determine the level of corrosion. There are multiple ways to mitigate corrosion, ranging from materials of construction to hydrogen sulfide control. Let's take each one of these separately. Municipalities can deploy non-reactive materials of construction that include wet well linings, pipe liners, or corrosion-resistant piping materials, such as plastic. Unfortunately, a large portion of collection systems in the U.S. are made of concrete or other types of materials and it may not be economically viable to change to non-reactive materials. In addition, the materials of construction fail to address potential health risks associated with the exposure to hydrogen sulfide gas.
One of the most effective ways to eliminate the risks to infrastructure and the community for hydrogen sulfide exposure is to eliminate the hydrogen sulfide in the collection system. In our experience, the most effective method is to use chemical treatment. There are a number of different chemical products for hydrogen sulfide mitigation. Reactive oxidizers, which oxidize the sulfide, are commonly used to treat hydrogen sulfide. Biologically active nitrate solutions can remove and prevent the formation of sulfides. pH shift products keep the sulfide in the wastewater and prevent H2S from emitting to the atmosphere. Iron salt solutions react with the ionic sulfides in the water, capturing the sulfide and precipitating it as ferrous sulfide.
These are all very common chemicals that are well known to the industry, as are their environmental profiles. Evoqua offers a wide range of corrosion control solutions and can help our customers determine the best treatment for their application.
WW: What are some specific solutions that Evoqua can provide?
JM: Evoqua has several innovative products that address corrosion, odor, and provide additional benefits in wastewater collection systems. Our Bioxide® solution suite of products are calcium nitrate solutions that prevent and remove sulfides and treat multiple odor compounds in the collection system. Alkagen® solution prevents the release of hydrogen sulfide by raising the pH of wastewater, reduces the impact of fats, oils and greases (known as FOG) and provides a beneficial alkaline supplement to the plant.
ODOPHOS® iron salt solution prevents corrosion by precipitating the sulfide in wastewater, and aid in removal of phosphorus and solids removal as well. Hydrogen peroxide prevents corrosion by oxidizing the sulfide in the wastewater.
We also are able to enhance performance of all these products by incorporating our VersaDose® advanced dosing controllers, which have the capability of adjusting dosing rates based on wastewater characteristics. This allows the utility to adjust dosing based on environmental factors such as pH, wastewater flow, hydrogen sulfide levels, etc., which can result in a significant amount of chemical cost savings.
WW: What are the next steps if a utility wants to learn more?
JM: Any interested utilities should contact Evoqua to schedule a system evaluation. We have an experienced team of experts and engineers who will measure collection system hydrogen sulfide levels, flows, and system dynamics to determine the best solution for your application. We can proactively provide you with a solution to treat corrosion that will extend the life of your wastewater system, and significantly reduce the risk of costly repairs.
To learn more, please contact Calvin Horst (Product Manager): 941-359-7969 or [email protected].
Bioxide and Versadose are trademarks of Evoqua, its subsidiaries or affiliates, in some countries.
