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Hydrogen Sulfide Gas: Why You Should Be Concerned

What is Hydrogen Sulfide?

Hydrogen Sulfide (H2S) often is a colorless gas with a rotten egg odor, which is commonly referred to as ‘sewer gas’.  Hydrogen Sulfide is highly poisonous and highly corrosive in wastewater applications.  There are various problems associated with hydrogen sulfide generation, such as toxicity, noxious odors, and the generation of corrosive sulfuric acid.

We treat everything from small grease traps to some of the world’s largest industries with tanks that emit toxic levels of sulfide.  Below is a technical description of how sulfide is generated in collection systems, wastewater plants and storage tanks.  Feel free to email us at bugman@teamaquafix.com for more information.

Where does it come from?

Sulfur is present in human and livestock waste as organic sulfides, such as mercaptans and disulfides.  It is also present in rainfall, primarily over metropolitans areas, but the most common source of sulfide is in domestic wastewater as sulfate.  An industry can also generate sulfate/sulfide wastes that may contribute to sulfide levels in wastewater such as:

  • Sulfate- Seen in sea food processing or fermentation plants
  • Sulfide- Seen in tanneries and paper manufacturing
  • Sulfite
  • Thiosulfate
  • Decomposition of xanthates used in the mining industry (12).

These sulfide-containing contaminants will either be oxidized (react with metals to form insoluble metal sulfides) or be released to the sewer (8, 13).  When sewage becomes stagnant, H2S is generated in the anaerobic conditions.  H2S can start to form sulfuric acid in lift stations and wastewater treatment plants, which will corrode cement and steel structures.Biofilm_MicroenvironOur De-Sulph-A-Nator binds the sulfide to prevent these odors while VitaStim SRB disrupts the sulfur reducing biofilm.  DAZZeL Fresh is used to dissipate the odors over lift stations, wet wells, sludge holding tanks, etc.

Process of Sulfide Production

The process of hydrogen sulfide generation depends on pH, temperature, and reactant concentrations (11). Hydrogen sulfide gas in the sewer atmosphere may be adsorbed in the thin film of water that normally covers the sewer walls and may be partially oxidized to sulfuric acid by bacteria of the genus Thiobacillus (8).

Bacterial colonies and gas products are formed when bacteria in a wastewater system has favorable nutrient loadings and plenty of space above the water line.  These bacterial colonies tend to lower the pH and cause Thiobacillus to oxidize the H2S and secrete sulfuric acid, causing corrosion.  This corrosion is often called Microbiologically Induced Corrosion (MIC) and can rapidly deteriorate cement and iron piping.

Toxicity Concerns

Hydrogen sulfide is a toxic concern for wastewater operators, especially if odor-masking agents are used, since it can affect the nervous system causing headaches, nausea, irritation of the skin, eyes, and respiratory tract, and at high doses it can cause death (2, 3). The high toxicity associated with hydrogen sulfide is due to its ability to bind to iron centers in mitochondrial cytochrome enzymes, which effectively stops cellular respiration and deprives essential organs of energy (3).  Although humans do possess enzymes in the liver that oxidize hydrogen sulfide to sulfate, high concentrations of hydrogen sulfide will overwhelm enzymes (3).  For more information see our Hydrogen Sulfide Toxicity Chart.

Sulfide Corrosion

Odor & Corrosion control for wastewater

Rusted Pipe caused by Hydrogen Sulfide (H2S)

 

Corrosion of metal and concrete is a major issue associated with the generation and oxidation of hydrogen sulfide.  High amounts of sulfuric acid (results from oxidation of hydrogen sulfide by Thiobacillus) lowers the pH of wastewater and contributes to the deterioration of concrete and pipe corrosion (7).

  1. Stainless Steel - Even stainless steel is subject to corrosion by bacteria, especially if the bacteria are incorporated in a slime film attached to the metal.  The slime film creates an anaerobic environment that allows sulfide reducing bacteria (SRB) to thrive and they contribute to iron sulfide formation, which diminishes the protective oxide film on most stainless steels
  2. Concrete – Concrete is a composite material made of sand, rock, and cement.  The cement that locks the sand and rock into place is vulnerable to the effects of hydrogen sulfide and acid attack (5).  The rate of concrete corrosion depends on the permeability of concrete and the amount of hydrogen sulfide gas that is adsorbed to the moist sewer walls (8).  Signs of prolonged exposure to mild acid attack include rust bleeding, cracking and spalling of the concrete (5).

Solutions:

De-Sulph-A-Nator:  Stops the sulfide and slows corrosion
VitaStim SRB:  Stops the sulfide and slows corrosion by destroying the biofilm
DAZZeL Fresh: Slows corrosion by destroying the biofilm

Applications/Solutions

Many wastewater facilities that experience sulfide problems generally use aeration, chemical oxidizers, such as hydrogen peroxide, and/or odor-masking agents (essential oils).  These only mask the underlying problem and do not actually remove the sulfur/sulfide molecules from the system, because of the reduction of sulfur into hydrogen sulfide
(H2S) or oxidation to sulfuric acid (H2SO4) causes the problem, removal of the sulfur molecule removes the problems of odor and corrosion from the waste stream (2).  Below you will find our solutions for specific applications:

Collection Systems

High concentrations of H2S can cause coatings and linings in collection systems and wastewater treatment plants to fail rapidly.  This increase in H2S is due in part to:

  • Longer detention and transport distances which increase the amount of septic wastewater.
  • More force mains and less gravity flow, which would promote aeration (1, 10);

Solutions:

De-Sulph-A-Nator:  Meter or drip into the lines to bind the sulfide
VitaStim SRB:  Toss into the line to disrupt the biofilm

Lift Stations

Hydrogen Sulfide can corrode the cement walls of lift stations. Corrosion makes the walls soft and brittle and can even result in your lift caving in, which is very expensive to fix.

Hydrogen Sulfide Corrosion in Lift Stations

Hydrogen Sulfide Corrosion in Lift Stations

Solutions:

De-Sulph-A-Nator:  Meter or drip into the lift station to bind the sulfide
VitaStim SRB:  Toss into the lift station.  It’s a good replacement for Ferric Chloride
DAZZeL Fresh: Spray over the lift station to dissipate the odors

Wastewater Treatment Plants

Poor settling, excessive sludge production, and corrosion are all results of high concentrations of H2S.  In wastewater treatment plants Hydrogen Sulfide can corrode the cement walls around the basin and guardrails.

Pitting and Corrosion in a Wastewater Plant due to Hydrogen Sulfide

Pitting and Corrosion in a Wastewater Plant due to Hydrogen Sulfide

Solution:

De-Sulph-A-Nator:  Meter or drip into the lift station to bind the sulfide

Grease Traps

Hydrogen Sulfide not only makes your grease traps smell bad, but it also corrodes the cement walls.

Solution:

De-Sulph-A-Nator:  Meter or drip into the lift station to bind the sulfide

Sludge Storage Tanks

Sulfuric Acid Pitting

Sulfuric Acid Pitting

Hydrogen Sulfide will make your sludge storage tanks smell bad, but it also corrodes the cement walls and metals leaving holes/pits resulting in unwanted leakage.

Solution:

De-Sulph-A-Nator:  Meter or drip into the lift station to bind the sulfide

Lagoons

Hydrogen Sulfide makes your lagoons smell bad and your customers upset.

Rotten egg odors and excess sludge in a lagoon

Rotten egg odors and excess sludge in a lagoon

Solutions (Best if used together):

OxyPaks XL: eliminates the rotten egg odor
VitaStim 6000 – Lagoon Sludge: Degrades excess sludge

Digestors

Digestors will begin to corrode and smell bad with the presence of H2S.

Solutions:

VitaStim SRB:  Toss a water-soluble packet in; it’s a good replacement for Ferric Chloride
DAZZeL Fresh: Spray around the digestor to dissipate the odors

Wet Wells

High concentrations of H2S will cause the cement walls to corrode.

Solutions:

DAZZeL Fresh: Spray around the digestor to dissipate the odors

Written by Kevin Ripp

Kevin Ripp

Kevin “The Bugman” Ripp is the owner of AQUAFIX; a state-of-the-art biological laboratory based in Madison, Wisconsin, producing custom bacterial and enzymatic products to treat wastewater.

AQUAFIX technologies are non-toxic to humans, wildlife, plants, domestic animals and fish.

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