Friday, September 2, 2011

Corrosion Protection for Wastewater Collection Systems

The human nose is extremely sensitive to the presence of hydrogen sulfide (H2S) and detects it "as the smell of rotten eggs" in concentrations as low as 0.0001 parts permillion (ppm). Hydrogen sulfide is often an indicator of the presence of

other odors as well as a potential corrosion problem. Corrosion is caused due to the acidic nature of hydrogen sulfide.
Corrosion Protection for Wastewater Collection Systems
Corrosion is caused due to the acidic nature of hydrogen sulfide in wastewater applications

Typically, wastewater-related problem odor compounds are generated in the liquid phase, during the process of conveying the wastewater from its inception to treatment area. While traveling through sewer lines, the wastewater can become anaerobic or septic (the dissolved oxygen can become depleted) as a result of the metabolic processes of microbes commonly found in wastewater.

Under anaerobic conditions, specific sulfate-reducing bacteria thrive. These microbes generate hydrogen sulfide (H2S) as a byproduct of their respiration. H2S has a low solubility in wastewater and when it escapes from the wastewater and moves into the air it is easily recognized by its characteristic offensive, rotten-egg odor. H2S can also be responsible for severe corrosion problems and toxic conditions within wastewater conveyance and treatment facilities.

Corrosion is caused due to the acidic nature of hydrogen sulfide. In underground sewers or other wastewater collection systems where visual inspection is not easily accessible, the development and concentration of hydrogen sulfide causes offensive odors and corrosion can often go undetected until significant damage or failure occurs.

Odor-causing wastewater is typically treated by altering the biological conditions in the wastewater or by adding chemicals to either control the formation of odor-causing compounds, or react with those compounds once they are formed. Liquid-phase treatment technology is most commonly applied in wastewater collection systems or during sludge storage/processing in the wastewater. However, liquid-phase treatment is often applied in a wastewater system for downstream control at the headworks of a treatment plant. Biosolids-handling facilities also have liquid-phase odor-control challenges that can be handled in a manner similar to the methods used for wastewater.

Among the liquid-phase treatments available, Siemens Water Technologies offers the patented products, Bioxide® and Aquit® solutions, proven treatment options that do not involve the handling of chemicals/materials classified as hazardous. Used individually or in combination, these liquid-phase odor control products promote the growth of favorable biology within the wastewater and have proven highly effective in eliminating the odors before release to the atmosphere.

Other options commonly used for liquid-phase odor control include the addition of oxidizing agents such as hydrogen peroxide and chlorine-based products, sodium or calcium hydroxides and precipitants such as iron salts. While effective, the handling issues of these hazardous agents have to be taken into consideration in the selection equation.

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