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Innovative pumping system diverts 75 mgd sewer flow during rehab project in Puerto Rico
Hydrogen sulfide (H2S) corrosion damage to wastewater treatment plant facilities often means time consuming and costly rehabilitation. This was the situation the Puerto Rico Aqueduct & Sewer Authority (PRASA) and the Puerto Rico Infrastructure Finance Authority (AFI) faced when H2S corrosion damage was discovered in both concrete piping and at two cast iron valve locations inside the Puerto Nuevo Wastewater Treatment plant.
To complicate matters further, the Puerto Nuevo plant is in the busy capital city of San Juan and handles 75 million gallons per day (mgd) of sewage.
Paramount to the successful completion of the $10 million rehab project to correct the H2S problems in the plant was ensuring that the sewage entering the facility could be safely diverted for a full four months while the repairs were being made.
“A bypass pumping system really was the only answer,” said Joe Abbott, national sales manager of Godwin Pumps, headquartered in Bridgeport, New Jersey. “The problem was that a bypass pumping system of this magnitude had never before been used on the island of Puerto Rico.”
In 1998, Godwin Pumps began working closely with AFI engineers to plan a pumping system to meet requirements for the bypass. AFI contacted Godwin Pumps because of Godwin’s reputation in the industry and its experience with this type and size job.
Godwin Pumps has supplied pumping equipment for bypasses as large as 150 mgd. However, Abbott commented, “We’ve been very successful with small bypass jobs as well — 1 mgd to 20 mgd.”
Ultimately, Godwin Pumps’ role was to devise a way to safely divert the 75 mgd of sewage around the area where the repairs were to be made. Any leaking of the bypass system was unacceptable.
Abbott said part of the challenge was that there was a 25-foot suction lift from the inlet channel to the grade. “This meant that the bypass pumping system had to draw 55,000 gpm at a critical suction lift of 25 feet,” said Abbott. “The Godwin Dri-Prime® was ideal for this situation.”
A totally automatic self-priming pump, the Dri-Prime will pump to 28 feet of suction lift. In addition, it is capable of running dry without damage which is ideal for intermittent flow conditions and peak periods. Specifically, the Godwin DPC 300 model Dri-Prime pump was selected for its ability to handle high volume flows. Ease of installation and fuel efficiencies were also factors in pump selection.
The bypass solution devised by Godwin Pumps to divert the flow entering the plant included 20 Godwin Dri-Prime DPC300 12-inch, diesel-driven pumps; 22,000 feet of 18-inch HDPE pipe; two fusion machines; and 10 specially designed discharge manifolds, each channeling two pumps into one main discharge line.
This 20-pump system proved to have the capacity needed to handle the daily average or peak flow and then some.
“The amount of pumping power provided a safety zone in the event storm water entered the system,” Abbott said. “Our pumping system provided the capacity to handle up to 100 mgd if necessary.”
Piping design was another key to this successful pumping system. Godwin engineers knew that thousands of feet of HDPE pipe would be required to divert the flow. Part of the challenge of this project was the existence of a primary and secondary discharge point. So the system had to accommodate higher discharge pressures. A CAD drawing was supplied by Godwin Pumps to facilitate the pipe installation. Because of the size and complexity of the piping system, two fusion crews were required to fuse thousand of feet of HDPE pipe on site. Then, working with the contractor, the installation began.
After weeks of preparation, the contractor, the local Godwin distributor — Puerto Rico Wire Products — and Godwin Pumps personnel put the bypass pumping system into operation. Over the next four months, while work was under way to address the maintenance problems in the plant, the Godwin team worked to oversee the system’s operation.
“This worked out really well,” said David Higgs, Godwin regional sales manager who served as project manager on this job. “Puerto Rico Wire’s involvement allowed Godwin Pumps’ U.S. crews to work with Bermudez & Longo’s project engineer Manuel Pelayo to get the system up and running. At that point, Puerto Rico Wire was able to take over and handle weekly routine maintenance.”
Higgs added, “It was a perfect example of international teamwork between all three organizations involved. The result was a successful design of a complex system.”