Dewatering
Headworks : Small Island with Big Needs
By Michele LaNoue
Jul 9, 2009 - 10:52:44 AM

Houston, TX -- Even though it is a small island, Puerto Rico has historically had big issues with sewage treatment. Due to its tropical location in the Caribbean, heavy storm events can bring unusually large peak flows into the treatment plants. Up until recently, these peak flows were handled by equipment that may have not been designed for such extreme conditions. As a result of this, damages and inoperability became a common and recurrent problem.

This is especially true in the case of “single rake” screens, which were installed in several sewage treatment plants on the island in recent years. A single rake or “climber screen” typically consists of an arm with a single rake and an attached gearmotor, which travels to the bottom of the channel in order to pick up the screenings and discharge them at the operating level. This design presented three serious problems for the plant operators in Puerto Rico: First, due to the unexpected increase in water depth during storm events, the gearmotors would submerge in the sewage and get damaged.

Second, in deep channels, the cleaning frequency of a single rake would be so long that the accumulated screenings would quickly blind the screenfield, resulting in flooding of the sewage over the decks. And third, due to a lack of engagement at the bottom of the screen, the single rake would simply bypass the screenings without removing them from the screenfield, again resulting in blinding of the screenfields and the obvious problems that creates.

In 2006, as part of a trip aimed at identifying high quality and reliable equipment manufacturers, the representatives of the Puerto Rico Aqueduct and Sewer Authority (PRASA) visited the Greenway WWTP in the City of London, Ontario. There they saw two Headworks multiple rake bar screens installed in 13 meter deep by 1.6 meter wide channels. They were immediately impressed by the performance and robustness of the units. PRASA was looking at replacing failing single rake screens at the Caguas WWTP. They were experiencing serious problems with these screens. When the PRASA representatives saw the Headworks screens they immediately realized they had found what they were looking for!

With the critical collaboration of INECO, Headworks distributor in Puerto Rico, the first of three screens was installed at the Caguas WWTP only a few months after the Canada visit. The results were immediate: no more problems due to submerged gearmotors, no blinding of the screenfield, no need to stop the plant to repair the screens and most important, the screens handled peak flows effortlessly.

The Headworks screen, installed in a channel 29ft deep by 4ft wide and with bar spacing of 0.5" was designed to handle peak flows of up to 28mgd. The screen is manufactured in SS 316 with a robust structure that can withstand the most extreme storm conditions and the impact of heavy debris. The multiple rake system provides a cleaning frequency of 10 sec at normal speed and 5 sec. at high speed, thus maintaining the screenfield free of obstructions. The lower sprocket system ensures the perfect engagement of the rakes between the bars and the auto-reversing feature virtually eliminates the risk of jamming caused by large debris reaching the screens, a common problem in Puerto Rico’s sewage plants.

Israel Almodovar, Manager of Regional Systems for PRASA’s Eastern Region stated: “We are very pleased with the performance of the Headworks bar screen at Caguas.”

The results were so positive that PRASA soon afterwards ordered the remaining two screens from Headworks in order to complete the full replacement of screens at Caguas. These two screens were installed last weekend and will allow the operators to sleep soundly even during the worst storms to hit the island!

Source: http://www.headworksusa.com/



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