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A civil engineer in Nevada was in charge of a pump station project requiring him to manage the cleaning, or ‘stripping’, of a sewer force main.
In municipal wastewater treatment scenarios, there have always been problems with wastewater build up in force mains. This build up can be anything from grease to bacterial slime growth and causes major problems for public utilities.
Air release valves clog and pressure build up will result in a decrease of wastewater flow. Build up in force mains will also increase anaerobic bacteria growth. Anaerobic bacteria live behind the slime layer in force mains and feed on the sulfates in wastewater. This results in the release of hydrogen sulfide which is corrosive and can be dangerous to utility personnel. It will also lead to community and residential odor complaints.
In this specific wastewater flow application, the civil engineer was tasked with cleaning a 4″ HDPE force main that is approximately 5900′ long. The customer was experiencing increasing pump head conditions and diminished wastewater flow rates over time. The customer also expressed a concern about the possibility of hydrogen sulfide formation due to long wastewater retention times in the force main from the collection system to the treatment facility.
Due to detailed data provided to Aulick by the civil engineer, Aulick personnel were able to determine an exact feed rate of our 225 Force Main Stripper (225 FMS); with a 4″ line that is 5900′ in length, the surface area of the force main is approximately 6,175 sq. ft. Based on these facts, Aulick personnel determined chemical feed rate and recommended a 2-day feed period due to contact time.
Furthermore, Aulick’s recommendation included the application of 225 FMS at approximately 75% of the total feed the first day, followed by the remaining 25% of the total feed on day two (225 FMS acts as a Chemical PIG).
Additionally, Aulick provided detailed application instructions to the customer; turn lift station pumps to HAND with a normal level of wastewater in the lift station. Add 225 FMS and pump the lift station down. Once completed, turn the lift station pumps back to AUTO and resume normal operation allowing the 225 FMS to get into the 4″ HDPE force main all at once. As the lift station pump pushes it down the line, it also scours the line. Repeat this process the next day with remaining 225 FMS.
Finally, Aulick made the recommendation to complete this step every 3 or 6 months to ensure optimal wastewater flow in the force main.
Learn more: 225 Force Main Stripper
When the 225 FMS Pails were received in Nevada from Aulick, the customer dosed for the recommended 2-day feed period. They started at a 142 GPM pump rate and the next day were at 197 GPM. The customer was extremely happy with the results and would be monitoring the pump station for the next few weeks. After an additional 2 weeks, pumping capacity increased further to 221 GPM.
These results enabled the customer to operate this specific pump station at a more optimal flow rate resulting in a decrease of production costs and an increase in gallon per minute pump rate.