Stop the Sulfide

Hydrogen Sulfide is a concern in wastewater collections systems, drain lines and in tanks. Hydrogen sulfide (H₂S(g)) is a colorless gas with a characteristic rotten egg odor.  There are various problems associated with hydrogen sulfide generation, such as toxicity, noxious odors,  and the corrosive sulfuric acid generated.  We formulate two chemical and one biological product to control sulfide.  Which one you use depends on your application and budget.

De-Sulph-A-Nator works by binding and preventing the sulfide from becoming odorous.

• Poured or metered into Grease Traps, dripped or metered into sewer lines and wastewater tanks.
• Great in applications for long detention times.

VitaStim  SRB (Sulfide Reducing Bacteria) works by disrupting the biofilm that causes sulfide generation. 

• Used in sewer lines and wastewater tanks.
• An added benefit of this products is its ability to digest fat, oil, and grease.

DAZZeL Fresh works by chelating the sulfide chemistry and disrupting the biofilm.

• Used in wastewater tanks or atomized above tanks to chelate airborne sulfide.
• Can be formulated to work in oil based solutions that generate sulfide.
• Also prevents mercaptan odors.
• Great for Septic Haulers who discharge to cities with tough odor standards.
• Also helps to break up fat, oil and grease.

We treat everything from grease traps to small cities to some of the worlds largest industries that have tanks that emit toxic levels of sulfide.     The technical information below describes the mechanism for sulfide generation and how our products work.   Feel free to email us at bugman@teamaquafix.com for more information.  Below is a technical desciption of how sulfide is generated in collection systems, wastewater plants and storage tanks.    For many people this technical information may be too detailed but we are a research driven company and for some applications this detail will prove helpful.

Present day high concentrations of hydrogen sulfide cause traditional coatings and linings in collection systems and waste water treatment plants to fail rapidly.  This increase in H2S is due in part to: longer transport distances, which increase the amount of septic wastewater; more force mains and less gravity flow, which would promote aeration (1, 10); and less heavy metals in the wastewater (5).  Without atmosphere exists aeration is obstructed leading to precipitation as the only sink for sulfide (11).

The diagram below shows how the sulfide is generated.  In municipal sewer lines, lift stations and in grease traps we will meter or drip De-Sulph-A-Nator into lines to bind this sulfide or we just toss VitaStim SOB into the line to disrupt the biofilm, or we may do a bit of both.  These products are added upstream of the problem and therefore they keep the problem from developing.

Generation of sulfate/sulfide waste

Sulfur is present in human and livestock waste as organic sulfides, such as mercaptans and disulfides, and in rainfall (SO4 2-) primarily over metropolitans areas and the most common source of sulfide in domestic wastewater is sulfate.  Industry can also generate sulfate/sulfide wastes that may contribute to sulfide levels in wastewater include: sulfate (sea food processing or fermentation plants), sulfide (tanneries, paper manufacture), sulfite, thiosulfate, or 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 atmosphere in partly filled sewers (8, 13).

Release of H2S(g) from liquid and resulting odor problems:

The release of H2S(g) into the sewer atmosphere results from the emission of molecular hydrogen sulfide from the water phase (1).  Sulfide in collection systems is mainly produced when sulfate is used as the terminal electron acceptor by obligate anaerobic sulfur-reducing bacteria (11).   Our De-Sulph-A-Nator binds the sulfide to prevent these odors while VitaStim SOB disrupts the sulfur reducing biofilm.

Overall 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). 

Bacteria in a municipal or industrial wastewater system with favorable nutrient loadings combined with facultative conditions and plenty of space above the water line cause the formation of bacterial colonies and gas products above and below the water line. These bacterial colonies tend to lower the ph and cause Thiobacilli to oxidize H2S and secrete sulfuric acid which causes the corrosion. This corrosion is often called microbiologically induced corrosion (MIC). This sulfuric acid induced corrosion can rapidly deteriorate cement and iron piping.

At AQUAFIX our focus is on addressing the root cause of the issue and either using our De-Sulph-A-Nator to bind the sulfide or using our DAZZeL Fresh of VitaStim SRB to clean the biofim that grows on the surface. Went want to stop the spread of the thiobacilli. Slowing the growth of the bacterial biofilm will slow the corrosion and the problem.

Biofilm in collection systems:

The majority of the sulfide produced is assumed to result from anaerobic sulfate reduction in the anaerobic regions of biofilms covering the submerged and wetted sewer walls (11).  The sulfides produce in the biofilms will diffuse toward the water phase and if the DO is high, the sulfide will be oxidized in the outer aerobic parts of the biofilm (14).  Sulfide does not enter the water phase if the DO is above 1 g/m (15). Metal sulfides accumuated in the biofilm can no longer be emitted or transformed (8)

Toxicity:

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 and nausea, irritation of the skin, eyes, and respiratory tract, and at high does (exceeding 700 ppm) 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, which is then excreted in urine (4), concentrations of hydrogen sulfide exceeding 700ppm overwhelm human hydrogen sulfide oxidative enzymes (3). 

For more information see our Hydrogen Sulfide Toxicity Chart.

Corrosion

Corrosion of metal and concrete is a major issue associated with the generation and oxidation of hydrogen sulfide.   The high amounts of sulfuric acid that occurs as a result of oxidation of hydrogen sulfide by Thiobacillus spp. lowers the pH of wastewater, contributes to the deterioration of concrete, and promotes ferrous pipe corrosion (7).   Our VitaStim SOB and DAZZeL Refresh help to destroy the biofilm.   Oxidation of hydrogen sulfide also affects the following surfaces.

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 sulfur-reducing bacteria (SRB) to thrive and they contribute to iron sulfide formation, which diminish the protective oxide film on most stainless steels (7). 

Concrete

Concrete, a composite material, is made of sand, rock, and cement.  The cement, a mixture of minerals and water locking the sand and rock into place, is most vulnerable to the effects of hydrogen sulfide and acid attack (5).  Bacteria, such as Thiobacillus spp., oxidize sulfur compounds and produce sulfuric acid that react with cement in concrete and corrode steel and iron (8, 5).  The rate of concrete corrosion depends on the permeability of concrete and the amount of gaseous hydrogen sulfide that is adsorbed to the moist sewer walls (8).  Signs of prolonged exposure to mild acid attack include rust bleeding and cracking and spalling of the concrete (5). 

Ettringite

Ettringite is naturally formed in the process of concrete setting but becomes a concern when it becomes soluble and leaves the original location to re-crystallize in larger spaces which can cause the expansion of deteriorating concrete.  Concrete is rigid and somewhat brittle so expansion and cracks can occur if there is not enough voids to accommodate the newly formed ettringite (9). 

In anaerobic reactors or regions of limited DO:

In the presence of sulfate, acidogenic, acetogenic (AB) and methanogenic (MB) bacteria compete with sulfate reducers for available substrates (12).   At COD/sulphate ratios >0.67, the complete removal of sulfate occurs if methogenesis also occurs, but at lower ratios the amount of organic matter is insufficient for complete reduction of the sulfate (12). 

Disadvantages and advantages of anaerobic reactors:

Toxicity of hydrogen sulfide to an aerobic WWTP microbial community:

Sulfide is toxic at higher concentrations for many bacteria.  It is assumed that it interferes with the assimilatory metabolism of sulfur or it may alter intracellular pH (12).  Sulfide-rich wastewaters generally contain high concentrations of cations such as Na+ and Ca 2+ (12), some of the Ca 2+ cations present can precipitate out as Ca3(PO4)2 which can lead to phosphate deficiency (12). 

Many sulfate reducing bacteria are less sensitive to organic overloads and to toxic upsets from: aeromatics (toluene, ethylbenzene), alkanes, chlorinated compounds (chloroform) and long chain fatty acids and can out-compete other anaerobic bacteria especially is there is an adequate supply of hydrogen gas available (12).

SRB and other specific bacteria:

Sulfate-reducing bacteria (SRB) are obligate anaerobic bacteria that can be broken into two broad nutritional groups (7).  The first group can achieve partial oxidation of a limited range of carbon sources, such as lactate to acetate, while the second is capable of oxidizing a wide range of carbon sources, such as fatty acids, to acetate or completely to CO2 (7).    Hydrogen can be a substrate or a product for sulfate-reducing bacteria. Desulfovibrio vulgaris and D. desulphuricans, use the oxidation of hydrogen as energy to grow (7), while Desulfovibrio desulfurican is a sulfur-reducing bacteria that produces hydrogen sulfide under anaerobic conditions.  Most SRB do not compete well with facultative anaerobic bacteria that use nitrate as a hydrogen acceptor.  We use our VitaStim SOB to compete with these bacteria or our De-Sulph-A-Nator to bind up the sulfur in the environment.

A few facultative anaerobic Thiobacilli such as T.denitrificans can also carry out anaerobic respiration, using lactate and nitrate as the terminal electron acceptor, while oxidizing the elemental sulfur to sulfate as long as a source of ammonia is present.

Other bacteria that oxidize hydrogen sulfide to sulfur include: Chromatium and Chlorobium and Beggiatoa (19). 

Solutions:

Many wastewater facilities that experience sulfide problems generally use aeration, chemical oxidizers, such as hydrogen peroxide, and/or odor-masking agents such as essential oils, but these only mask the underlying problem and do not actually remove the sulfur/sulfide molecules from the system.   Because 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).

References:

1. Yongsiri, C., Vollertsen, J., and Hvitved-Jacobsen, T.  (2004).  Hydrogen sulfide emission in sewer netrworks: a two-phase modeling approach to the sulfur cycle.  Water Science and Technology 50(4): 161-168
2. http://www.isa.org/Template.cfm?Section=Communities&template=/taggedPage/DetailDisplay.cfm&ContentID=33759ISA
3. http://emedicine.medscape.com/article/815139-overview
4. http://www.inchem.org/documents/cicads/cicads/cicad53.htm
5. Hampton Roads Sanitation district Coatings Manual (2006).  Appendix A: Basics on corrosion in wastewater collection and treatment system: the corroding environments and Material
6. http://freepatentsonline.com/4879240.html
7. Hamilton, W.A. (1985) Sulphate-Reducing Bacteria and Anaerobic Corrosion. Annual Review of Microbiology 39: 195-217
8. Nielsen, A.H., Yongsiri, C., Hvitved-Jacobsen, T., and Vollertsen, J. (2005). Simulation of sulfide buildup in wastewater and atmosphere of sewer networks.  Water Science & Technology 52(3): 201-208
9. http://www.cement.org/tech/faq_DEP.asp">http://www.cement.org/tech/faq_DEP.asp
10. Tanaka, N., Hvitved-Jacobsen, T., and Horie, T. (2000).  Transformations of Carbon and Sulfur Wastewater Components Under Aerobic-Anaerobic Transient Conditions in Sewer Systems.  Water Environment Research 72(6): 651-664
11. Nielsen, A.H., Hvitved-Jacobsen, T., and Vollertsen, J. (2006).  Recent findings on sinks for sulfide in gravity sewer networks.  Water Science & Technology 54(6-7): 127-134
12. Hulshoff Pol, L.W., Lens, P.N.L., Stams, A.J.M., and Lettinga, G. (1998).  Anaerobic treatment of sulphate-rich wastewaters.  Biodegradation 9: 213-224
13. Pomeroy, R. D., and Parkhurst, J. D. (1977). “The forecasting of sulfide buildup rates in sewers.” Progress Water Technol., 9(3), 621–628.
14. American Society of Civil Engineers (ASCE Manual and Reports on Engineering Practice), (1998). Sulfide in Wastewater Collection and Treatment Systems
15. Hvitved-Jacobson, T. (2002).  Sewer Processes - Microbial and Chemical Process Engineering of Sewer Networks.  CRC Press, Florida, USA.
16. Kamp, A., Stief, P., and Schulz-Vogt, H.N. (2006)  Anaerobic Sulfide Oxidation with Nitrate by a Freshwater Beggiatoa Enrichment Culture.  Applied and Environmental Microbiology.  72(7): 4755–4760
17. http://technology.infomine.com/environmine/ard/microorganisms/roleof.htm
18. http://filebox.vt.edu/users/chargedor/biol 4684/cycles/soidat.html
19. “Sulphur cycle & microbes” from b.stev presentations accessed 2009.
20. http://water.me.vccs.edu/concepts/chlorochemistry.html

Questions or Comments? Please call or email us with your concerns. Our advise is comprehensive yet practical.

• Call us at 1-888-757-9577 (8:00 am – 5:00 pm CST, M–F)
• Send an e-mail to bugman@teamaquafix.com