Choosing the Right Screens

Durable bar screens provide protection for a Build-Operate-Transfer project in Reynosa, Mexico

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Reynosa is a city in the Mexican state of Tamaulipas, across from McAllen, Texas. Tecnologia Intercontinental (TICSA), one of Mexico’s top contracting firms in the wastewater sector, won the contract for two wastewater treatment plants for this city.

"We are involved in Build-Operate-Transfer (BOT) projects for municipal wastewater treatment plants in Mexico,” explained Roberto Primelles, technical director at TICSA. “In the majority of these contracts, we are responsible for the operation of the plants for periods of up to 20 years. The biggest problem we have experienced with mechanical screens in the past is that the screens fail to perform as promised. Many screens we have used in the past have required continuous repairs and we’ve also had some cases where the screens had to be completely refurbished or even replaced after a very short time. As a result of this, and being BOT contracts, we have to absorb the cost related to the refurbishment/replacements of the screens, plus we also have to deal with any other costs which are a consequence of the screens' improper work, such as clogging or even damages of equipment downstream.

“To make matters worse, the sewers in many parts of Mexico tend to bring all kinds of large and heavy items to the plants. The screens, being the first line of defense, have to be strong enough to not only cope with these items, but also to effectively screen them out and continue working. If you combine this with a 20-year operations contract, you can understand why we are so concerned about choosing the right screens.”

Unlike many of the mechanical screens currently available in the market, the Headworks Mahr Bar Screen will withstand such abuse for 20 years or more, requiring only basic spares and minimal maintenance. In the long run, therefore, its lifecycle cost is exponentially lower over the years than that of its "less expensive" competitors.

“The first Headworks bar screen we bought was installed in the first semester of 2006 in a WWTP in Mexico City. This screen has been working non-stop since then, with absolutely no problems of any kind. The maintenance so far has been minimal, mostly consisting of simple routine visual inspections. After this great experience, we decided to work with Headworks on the Reynosa project. We wanted to replicate the great results we achieved at the Mexico City plant.”

Four Headworks Mahr Bar Screens were installed in channels 6.5 ft deep by 8.2 ft wide in Reynosa. Each screen handles approximately 31 million gal per day (mgd) of influent. In addition to the Mahr Bar Screens, one of the two plants required a Perforator, a perforated-plate screen with 3-mm openings, for a channel 6.5 ft deep by 4.6 ft wide. This Perforator handles 24 mgd of peak flow.

The bar screens were started up at the beginning of 2009 (the plant where the Perforator is installed has not yet initiated operations). In November 2009, Primelles stated:

“After 10 months in operations, we have not had any kind of problems and we are extremely satisfied with the performance and reliability of the Headworks bar screens at Reynosa. The screens have been successfully dealing with all the items and trash that reach the plant. We have not experienced any type of jamming that would have forced us to stop the plant and we haven't had any incidents of screenings passing through and reaching the equipment downstream. Overall, we are extremely satisfied.”

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