El Centro, a city 100 miles east of San Diego, was experiencing signiﬁcant issues with odour control in its sewer system, despite many different attempts from different chemical dosing suppliers to resolve the issue.
Rotten egg gas (H2S) measurements at some man-holes in the system were exceeding 4000ppm, which is both highly dangerous as well as highly corrosive to the system.
Broke-up a fatberg and cleaned the line
Signiﬁcantly reduce hydrogen sulphide levels from 3000 ppm to 70 ppm
El Centro is city 100 miles east of San Diego, which sits on the Colorado canal system.
The city has a population of around 45,000 and runs its own wastewater treatment plant. Chemical dosing for odor control is carried out at a few lift stations.
Sewer line 3, designed to transport waste from Imperial Valley Mall, was particularly known for extreme odor issues. The city staff had unsuccessfully tried a variety of odor mitigation systems.
Sewer line 3 is a 12 inch diameter line that starts from the Imperial Valley Mall and increases to 27 inches by the time it reaches the lift station. It was designed to serve the projected population growth around the mall, however, this growth never eventuated, making the line too big for the relatively small volume sewer ﬂow.
The ﬁrst and only lift station, E Villa Road is positioned roughly 2 miles from the start of the line. The retention time from the lift station to the treatment plant is roughly three days with a ﬂow of 0.13 million gallons per day (MGD). While the retention time in the gravity ﬂow up to the lift station is estimated to be around four days. A reverse syphon, upstream of the lift station adds to the challenge.
Due to these factors very high H2S readings, around 3,000 ppm, were measured in this sewer line.
The city tried dosing various chemicals to mitigate the odors, including enzymes and bacterial treatment products. However, these methods were unsuccessful and only marginally reduced the H2S.
We took on the challenge and committed to reduce the odor to manageable levels. The solution was to methodically and consistently dose magnesium hydroxide liquid at strategic locations. Due to the unusually long retention time, the beneﬁts of dosing magnesium hydroxide for odor reduction were not be apparent for some weeks.
The magnesium hydroxide dosing started at the E Villa Road pump station at the end of January, 2019. The odor level before dosing magnesium hydroxide was very high (Fig 3). A few weeks of shock dosing at a higher dosing rate of 80 to 100 gln/MG was carried out. This was followed by dosing in the upstream manhole along with the dosing at the lift station.
Magnesium hydroxide has a higher neutralising value per kilo when compared with caustic while being significantly safer to handle than other traditional alkalis, making it a very safe and cost competitive option for hydrogen sulphide gas (H2S) control in sewers.Find out more
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