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Jea's Experience With Magnesium Hydroxide for Collection System Odor Control: “It's not your mother's milk of magnesia”

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Abstract:

JEA is a regional utility serving Northeast Florida providing electric, water, wastewater and chilled water services to approximately 900,000 accounts. JEA owns and operates 5 regional and 10 local water reclamation facilities, 40 water treatment facilities and over 1,200 sewage lift stations in four counties. Large collection systems with large manifold sewer force mains combined with high temperatures and high sulfate levels in the potable water source contribute to high hydrogen sulfide (H2S) levels in the system. The local government also has local air emission regulations that require JEA to ensure that there are no detectable odors from the sewer collection system.

Until recently, JEA used a combination of liquid phase treatment using hydrogen peroxide and vapor phase treatment using a caustic scrubber and carbon units to treat odors from the Arlington-area sewer manifold system. This treatment method had a cost of approximately 400,000 per year and JEA was still receiving odor complaints from several locations. After several months of investigation, JEA decided to pilot test magnesium hydroxide to lower the H2S level upstream from a major pump station on the Arlington manifold. This would allow the caustic scrubber at this location to be eliminated and the remaining H2S at the station to be treated by a Marcab Iron Sponge. The pilot test successfully lowered the H2S level in the wet well from over 1,000 ppm to an average of 50 ppm, a level easily treated by the on-site iron sponge. This represented an annual cost savings at this station alone of over 200,000.

After the successful pilot test, the product was expanded to treat two-thirds of the Arlington collection system with the remaining portions being treated with Hydrogen Peroxide. Since beginning this project, JEA has received one validated odor complaint which was due to a failed chemical pump. A side benefit was also gained. The Bradley Road master pump station had a continual grease problem that required three full days of cleaning about every 3-4 weeks to eliminate a 2-3' deep grease layer in the wet well. With the addition of magnesium hydroxide, the grease did not accumulate and cleaning has been reduced to less than two hours per month.

Magnesium hydroxide works in H2S reduction by: a) neutralizing the first hydrogen ion in the H2S molecule, b) shifting the pH to scavenge free H+ and favor the HS species, c) shifting away from a favorable pH range for SRBs and d) forming polysulfide compounds that prevent downstream flare-off during mixing with side streams. Magnesium hydroxide works in FOG reduction by: a) slowly dissolving FOG accumulations at the FOG/water interface, and b) facilitating the biological reduction of FOG. Magnesium hydroxide makes fats, oils, and grease (FOG) more digestible by chemically breaking the large complex compounds into simpler organic compounds. Furthermore, magnesium hydroxide enhances O2 and CO2 gas transfer at the air/water interface by breaking down the FOG blankets that can arrest biological digestion at the FOG/water interface.

Overall, the addition of magnesium hydroxide to the mix of chemicals used by JEA for odor control has saved JEA over 400,000 per year in chemical and maintenance costs and has eliminated several problematic odor complaint areas. This paper will describe how this chemical works in a collections system, methods and results of the pilot test and JEA's long term experience using this chemical for controlling odors in the collection system.

Document Type: Research Article

DOI: https://doi.org/10.2175/193864708788807718

Publication date: 2008-01-01

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