White Paper: The Use Of Magnesium Hydroxide Slurry As A Safe And Cost Effective Solution For H2S Odor, Corrosion, And FOG In Sanitary Sewer Systems

By Aileen Gibson, Product Development Manager, Martin Marietta Magnesia Specialties LLC.
Steve Leykauf, Sales Engineer, Martin Marietta Magnesia Specialties LLC.
Chris Knapp, Process Engineer, Martin Marietta Magnesia Specialties LLC.

Disengagement of Federal involvement in wastewater infrastructure build-out and maintenance as evidenced by dramatic decline in Federal funding has left many municipalities short on the means to conduct a demanding responsibility. Maintaining wastewater infrastructure is a challenge for many municipalities, particularly in areas where there are long retention times in the collection system, high sulfur content and a high concentration of fats, oils and grease (FOG) that can lead to the formation of hydrogen sulfide (H₂S) gas. The use of magnesium hydroxide (Mg(OH)₂) as a treatment agent is a significant development in wastewater management in the last 30 years.

Although the job of controlling water pollution remains unchanged, wastewater characteristics have changed from the beginning of publicly-owned treatment works (POTW) in the early 1900's until the present. During the last 25 years, regulatory changes that were designed to help make sure that some parts of the environment were protected, have resulted in a deterioration of municipal wastewater infrastructure. These changes have fundamentally altered the physical, chemical, and biological properties of wastewater, making treatment more challenging to wastewater professionals than ever before.

Hydrogen sulfide has increased in recent years. Sulfides have risen steadily from the early 1980's to the 2000's due to longer retention times caused by urban sprawl with centralized treatment, and change in wastewater biochemistry due to pretreatment legislation. To protect public health, the Environmental Protection Agency's (EPA) 1983 Categorical Pretreatment Act severely reduced metals limits for industrial dischargers. Heavy metals react with dissolved sulfide in wastewater and render it insoluble. In the absence of metals, the dissolved sulfide concentration has increased over the last twenty years. With longer retention times through the sanitary sewer system, the wastewater becomes anaerobic which favors sulfate reducing bacteria (SRB). As a result, H₂S gas forms which imparts a rotten egg odor.

Corrosion in the sanitary sewer system occurs when H₂S is biologically converted to sulfuric acid by Thiobacillus bacteria. Although reducing metals was necessary to protect public health, pretreatment has contributed significantly to increased sulfides, leading to heightened H2S odor and ultimately to accelerated corrosion. The implications of hastened corrosion are clear. In 2000, EPA estimated that municipal sewers are failing six times faster than their rehabilitation rate. The EPA predicts that by 2016, over 50% of the United States' 600,000 miles of sewer lines will be in poor, very poor, or inoperable condition.

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