Benton Process Washwater Pump Station saves water, money

posted by: Karen Bonvillain | 10th February 2015
Benton Process Washwater Pump Station saves water, money

This article was published in the February 2015 issue of City & Town, by the Arkansas Municipal League. Written by Matthew Vinyard, P.E. a Project Manager at McClelland Consulting Engineers, Inc.

 

In 2010 Benton Utilities began to realize their use of potable water was an issue that needed to be addressed and changed. It was estimated they were using in excess of 10 million gallons of potable water in various applications at the wastewater plant each month. Another way to look at it was they were using approximately 460,000 gallons of potable water a day as process water in dewatering and sludge handling facilities as well as sprayers and yard hydrants throughout the plant.

Benton needed a design that would use non-potable water rather than potable water during treatment phases and curb the large amount of potable water usage. What started out as a collaborative engineering effort to save Benton Utilities money and potable water resulted in a savings of both and a sustainable project of which Benton can be proud. This plan would benefit the city and be a positive contribution to water and its conservation.

How it works

Simply put, the process begins when water is drawn from an existing 36-inch DIP downstream of the UV system and before the parshall flume where the effluent exits the plant. A 12-inch tapping saddle and gate valve was installed on the existing 36-inch DIP and connected to an eight-foot diameter wetwell. Water is drawn from the wetwell by two 500 GPM progressive cavity pumps then strained and pumped to the dryer and sludge press building, screens, digesters, and clarifiers. Existing piping to the dryer and press was used for non-potable water, and sections of piping were removed as required to ensure that a cross connection was not made between potable and non-potable water lines.

The non-potable water is used to clean the sludge from the belts and cool the dryer during operation. Non-potable water was connected to the outside of each screen building and the existing waterlines were cut and capped. The non-potable water is used for the sprayers on the screens. Separate yard hydrants labeled “non-potable water” were installed at the clarifiers and digesters for wash down purposes. A fire hydrant was also installed for various situations where large volumes of non-potable water are needed, such as when the street department may need water for maintenance. The illustration below shows a simplified schematic view of the process washwater pump station.

This project has saved Benton Utilities and the City of Benton in water production costs and it comes at a time when water conservation was especially needed since the existing water plant was reaching capacities during peak demands. This gave the utility an opportunity to save potable water, conserve power, and save money. The return on their investment has nearly come to fruition—the project will be paid off by June 2015.

The washwater system cost $414,717 to construct in 2011. The project was fully online beginning January 2012 and has been in operation for three years. A total of 222,451 million gallons (MG) of potable water have been saved since the system was in operation. Actual numbers show an annual savings of 62.643 MG in 2012, 72.612 MG in 2013, and 86.19 in 2014. Wholesale cost of potable water is $1.64 per thousand gallons. Based on this, the savings in water production cost per year is approximately $121,000. Therefore, the payback return on investment is projected to be summer 2015.

 

 

Matthew Vineyard, PE, is a Project Manager in McClelland Consulting Engineers, Inc.’s Little Rock office. Contact Matthew at 501-371-0272 or email mvineyard@mcclelland-engrs.com.

Matthew Vinyard, PE, is a Project Manager in McClelland Consulting Engineers, Inc.’s Little Rock office. Contact Matthew at 501-371-0272 or email mvinyard@mcclelland-engrs.com.

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