We often hear that wastewater has septicity when the water has black color, high sulfides, odors, and spirochetes/spirillum when viewed under the microscope. Today I want to define the conditions that cause septicity and how it can/should be addressed.
Conditions to create septicity:
Problems with septicity in collection systems
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.
In waste treatment we often only talk about sulfur when we have odor and corrosion problems related to hydrogen sulfide or H2S. While sulfur can be a problematic compound, it is also a vital micronutrient for life and is cycled throughout the environment by biological processes. An understanding of these processes can help waste treatment operators keep sulfur in its most “benign” forms and manage to prevent both excessive odors and corrosion.
A tracer study gives vital information on system hydraulic residence time (HRT), flow & mixing patterns, and information on potential short-circuiting. They are useful in a wide variety of applications including aerated lagoons, polishing ponds, and storm water treatment systems. While most people only focus on the discovery of HRT, some of the most vital treatment information comes from information on mixing and potential short-circuiting. In most cases, the basin volume is a “fixed” condition which is not going to change in the short-term. What we can change based on tracer study information is aeration/mixer placement and prove if curtains are needed or effective in their current placement.
A tracer study is done using a “conservative” material that passes through the system without significant adsorption or degradation. In most cases we use a lithium chloride salt or fluorescent dye. The presence and concentration of which can be readily measured using accurate lab procedures. Dosing is based upon generating a target initial concentration and them measuring concentrations at sampling points at set times for two theoretical residence times.
The sample data is then plotted to determine:
1. Time at first appearance
2. Peak concentration time
3. Peak concentration magnitude (amount of tracer)
4. Decrease in tracer concentration (time & pattern)
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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