Reduced Sulfur is converted back to sulfur and sulfate by microbial action. The most common bacteria found in this process are:
Photosynthetic Sulfur Oxidizers - Purple sulfur bacteria & green sulfur bacteria
Obtain energy for growth from the following reaction:
H2S --> So + 2H+ + 2e-.
Both purple and green sulfur organisms require substantial quantities of reduced sulfur (sulfide), anoxic/anaerobic water conditions (that generate sulfides), and sunlight exposure to be a substantial portion of the biomass. You can find photosynthetic sulfur oxidizers in lagoons systems such as sugar mills and paper mills during long daylight hour seasons. In cases the bacteria can even turn the water pink or purple. One problem with these organisms in wastewater is their tendency to float causing high effluent solids.
Chemolithotrophic Sulfur Oxidizers
Two main groups
Thiobacillus & Starkeya sp. – obtain energy by the following
H2S + 1/2O2 --> So + H2O + energy
So + 1½ O2 + H2O --> SO4 + 2H+ + energy
Of notes is the production of sulfuric acid as the final product of Thiobacilllus metabolism. As a group the Thiobacillus are found from pH near neutral down to as low as pH 2. Some of the lower pH Thiobacillus are partially responsible for acid mine waters found near mine tailing piles.
While most Thiobacillus and Starkeya are obligate aerobic microbes, one described species Thiobacillus denitrificans uses nitrate instead of oxygen.
Paracoccus denitrificans and Thiosphaera Pantotropha
Among the most
unique sulfur oxidizing microbes are Paracoccus denitrificans and Thiosphera pantotropha. These microbes have the ability to convert reduced sulfur into oxidized forms with the same chemical reactions as Thiobacillus. They also have the ability to grow using chemotrophic metabolism on odorous short chain volatile organics. This includes odor causing acetic, propionic and butyric acids.
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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