San José, Costa Rica, since 1956

San José to build sewage treatment plant

When you flush a toilet in Costa Rica, do you know where it ends up? Most likely, it goes directly into a local water source.

According to the World Health Organization, more than 96 percent of sewage produced in Costa Rica is untreated. Most of it ends up in rivers, which in turn flow into the ocean.

“Our rivers are open-air sewers,” said Francisco Brenes, project manager for the Costa Rican Water and Sewer Institute (AyA).

This is about to change.

Costa Rica is planning to open Central America’s largest sewage-treatment plant in 2015. The plant, to be named Los Tajos, will be located in La Carpio, a poor neighborhood on the northwest outskirts of San José, and aims to service more than 1 million Central Valley residents.

Currently, almost all sewage from the Central Valley ends up in rivers, eventually flowing into the Río Tárcoles and then the Gulf of Nicoya. In contrast with Costa Rica’s international image as a “green” destination, the Tárcoles has been called the most polluted river in Central America.

Waste from homes and businesses connected to the current sewage system, as well as those with septic tanks, all flow into the rivers. Jorge Herrera, coordinator for the Laboratory of Environmental Analysis at the National University (UNA), classifies the current state of Costa Rica’s rivers as grave.

“We have 64 points where we have monitored pollution in the rivers of the Virilla River basin [which passes through San José] since 2005. What we’ve found is that on average, 56 percent of our observation points present moderate to severe levels of pollution, meaning between 60 and 85 milligrams of oxygen per liter of water,” said Herrera, who cited “organic materials” as the primary cause. A healthy river should have 5 mg of oxygen per liter, and a “tolerable level” would be 25. “

It gets worse in the dry season,” Herrera said. “About 84 percent of our points present unacceptable levels of pollution, and it’s not getting better. We see between a 5 and 25 percent increase in [river] pollution annually.”

People living near these polluted rivers have a greatly increased risk of illness and infection. “These rivers are essentially dead,” Herrera said. “You can’t use them to water crops, or even for any industrial purposes. Navigation is the only use they have. And when farmers and industry can’t use the river, they get their water from wells, which in turn greatly taxes our aquifers.” 

The Los Tajos project would dramatically change that.

When finished, the sewage-treatment plant will include a revamped sewer system through 11 cantons in the Central Valley, as well as some 400 kilometers of new sewers. Thus far, AyA has expropriated 26 hectares for construction of the plant, and is in the process of buying 2,500 small lots where the new sewer lines will be built.

Initially, Los Tajos will provide only primary treatment, meaning that solid particles will be removed from the wastewater, but many contaminants will remain. Primary treatment includes removing about half of the solid particles from water before it goes back into the river.

AyA’s Brenes said that a second phase would begin in 2015 to add a secondary biological treatment of the water to greatly improve its quality before it reaches rivers. AyA is working on securing a $40 million loan needed to finance the second phase.

Work has already begun on rehabilitating old sewer lines, and new lines are being built. Brenes said that homes along the newly built public sewer lines will be checked for clandestine connections and septic tanks, and everyone will eventually join the new sewer system.

Construction on Los Tajos is set to begin at the end of April. However, the Ombudsman’s Office has to first rule on an appeal filed by a company that did not win the bid to build the plant. “We’re not worried about [the appeal],” Brenes said. “We haven’t lost an appeal yet.”

Los Tajos is part of the Project for Environmental Improvement for the San José Metropolitan Area, and is financed in part by a $150 million donation from Japan. The remaining $120 million for the project will come from the Inter-American Development Bank.

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