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Polyethylene Pipe Plays Role in Wastewater Treatment Plant Renovation

by Tyler Henning

The Town of Denton, Maryland installed a 400-foot-long high-density polyethylene (HDPE) pipe as part of needed wastewater treatment plant upgrade. The smooth-walled HDPE pipe is an important component in the treatment plant's enhanced nutrient removal upgrade. Within the 54-inch diameter DR 32.5 pipeline, chlorine has adequate contact time with effluent to disinfect the town's wastewater before being chemically de-chlorinated and released back into the environment.

The environment is of key concern in the Chesapeake Bay area, with Denton's treatment plant being one of the 67 major treatment plants deemed to have a big influence on the health of the Chesapeake Bay. In recent years, the bay has realized algae growth and worsening water quality.

The upgrade is an effort to lower the amount of nitrogen and phosphorous released into the Chesapeake Bay in accordance with the Chesapeake Bay Agreement of 2000.

I would definitely like the opportunity to work with it again on future projects

Jason Clopper

Legislation like the Chesapeake Bay Agreement of 2000 is not unusual to the Chesapeake Bay area.

The reduction of nitrogen and phosphorous is critical to the health of the Chesapeake Bay. Over the years, the water in the bay has experienced a decline in quality because of excess nutrients coming into the bay. The nutrients spur algae growth that blocks sunlight, suffocates seabed grasses and deprives some areas in the water of oxygen.

To combat the debilitating effects of the excess nutrient product, various programs and legislation have been put in place to try and reduce what goes into the Chesapeake.

As part of the Chesapeake Bay Agreement of 1983, the Denton Wastewater Treatment Plant received an upgrade to remove nitrogen through biological nutrient removal. Using the nutrient removal, Denton's treatment plant removed more than 90 percent of pollutants with a nitrogen concentration below 8 milligrams per liter total nitrogen.

When the Chesapeake Bay Agreement of 1983 ran out, a new agreement was signed. The new agreement set greater goals for reduction in nutrient pollutants entering the Chesapeake Bay from agricultural irrigation, stormwater runoff and wastewater treatment plants. Once upgraded, treatment plants like those in Denton were expected to reduce nitrogen and phosphorus in the wastewater, down to 3 milligrams per liter total nitrogen and 0.3 milligrams per liter total phosphorous.

The Town of Denton's Enhanced Nutrient Removal upgrade project was funded by the State of Maryland through the state's clean water revolving fund and a state grant. The total cost of the project was slightly more than $5 million.

"Once we're upgraded, we (the 67 major wastewater treatment plants in the Chesapeake Bay area) will have satisfied one-third (wastewater) of the Chesapeake Bay 2000 agreement, leaving stormwater and agriculture to comply," said Mark Chandler, manager of water and wastewater operations for the City of Denton. "We'll be performing at total compliance."

To upgrade the Denton Wastewater Treatment Plant, engineers installed post-anoxic reactors, deep-bed upflow de-nitrification filters and chemical feed systems.

Also as part of the upgrade, a key pipeline was excavated and replaced. Previously, a 33-inch corrugated HDPE pipe with integrated steel bands was used to host effluent to be disinfected over time. A chlorine contact chamber now allows even more detention time and provides optimum chlorination through plug-flow conditions.

An engineer on the project stated that "the interruption of the plant's hydraulic profile to include a deep-bed filter rendered the existing 33-inch pipe impractical for reuse. The loss of the pipe led to several hundred feet of piping length loss, or loss of contact time and volume for disinfection. In order to provide the same volume in a much shorter distance, we had to significantly increase the pipe size to 54 inches to make up for the lost volume. Polyethylene was found to be the most economical."

Lead contractor J.L.W. and Associates hired Ferguson Industrial Plastics to complete the pipe fusions on the project. Ferguson provided a fusion technician and McElroy MegaMc® 2065 fusion machine for the short fusion project.

The MegaMc 2065 used to fuse the pipe at the jobsite is one of the largest fusion machines in the world, with the ability to fuse pipe sizes from 20 to 65 inches (500mm to 1,600mm) in diameter.

Ferguson also fabricated a 45- and 22.5-degree ell using butt fusion that was used in structuring the pipe to fit the design needs of the project. The fabricated parts were trucked to the site, and fused onto the length of pipe before being installed.

Once pipe and fabricated piping were on site, 50-foot lengths of the pipe were fused together to create a long, monolithic pipeline. The 45- and 22.5-degree ell was fused to a shortened length of pipe approximately 25 feet long. A final tie-in fusion was performed, linking the long length of piping to the ell that would be installed into a bank of filters. The fusion process took less than two days.

"I have never worked with such a large diameter of this type of pipe (HDPE), but I found it to be almost as easy as working with smaller sized pipe," said Jason Clopper, superintendent on the site for J.L.W. and Associates. "I would definitely like the opportunity to work with it again on future projects."

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