May 11, 2001

Tijuana's Ecoparque: Decentralized Water Treatment and Water Reuse

by Greg Bloom

Tijuana is a city of steep, close hills and hills make centralized wastewater treatment plants expensive and large consumers of energy as sewage must be pumped over hill after hill until it reaches a large, often foul-smelling treatment plant that can cost close to US $1 billion to build. Many of Tijuana's hills are also crowded with homes or are covered in grasses that are brown much of the year. Other hills show signs of severe erosion or scars where they were cut into so as to create level building sites.
A view of Tijuana's Ecoparque.


Tijuana's Ecoparque, a simple, low-energy system that cleans wastewater and reuses it to irrigate a designated green area, provides an answer to all of the above mentioned problems. Ecoparque began in 1986 as a study by the Colegio de la Frontera Norte (Colef) of a decentralized system for wastewater treatment and reuse in urban areas (Sistema Decentralizado de Tratamiento y Reuso de Aguas Negras en Zonas Urbanas, SIDETRAN). An Ecoparque publication states that SIDETRAN is based on two premises, first that sewage is a valuable resource which is now being wasted and second that sewage must be managed in a decentralized way so as to maximize its usefulness within urban areas.

Ecoparque currently treats the wastewater generated by 10,000 people, about 900,000 gallons a day. As the treatment center is located about half way down a hill wastewater is drawn to it by gravity rather than pumped to it with electricity. Gravity also powers the plants Basic Treatment Unit, or BTU. The BTU includes an initial screen to filter out large waste like cans or sticks and a second, finer screen that filters out small organic particles. Every few hours this second screen is manually emptied into a compost pile where water and worms turn the waste into 800 kilograms per month of high-quality compost. The compost piles are odor free and no flies are attracted to the compost. The finished compost is later sold to area farmers who consistently buy up all of the compost that Ecoparque produces.

As the water continues downhill it passes through a tower where it moves its way through a PVC plastic biofilter maze. The water trickles drop by drop through the tower and becomes oxygenated which contributes to the growth of beneficial organisms within the plastic maze. These organisms then consume microscopic bits of organic material in the waste water thereby cleaning it. After this the water is then stored for eleven hours in a tank where sediment falls to the bottom of the tank. After eleven hours the water is pumped to the top of the tower and it goes through the biofilter again. The small pump used to move this water a short vertical distance is one of the only uses of electricity found in the Ecoparque. Finally, the water is again stored for eleven hours in the sediment tank and is then ready to be used to irrigate the surrounding hillside.



Oxygenation tower. Ecoparque Director, Martin Medina, center.

Like many border cities with rapid population gain and an overwhelmed infrastructure, Tijuana has few green areas and Ecoparque helps in the resolution of this problem as well. Before and after pictures of Ecoparque's hillside location are dramatic in their contrast. Previously the hillside was brown grass, bare earth and erosion scars. Today the hill is covered in flowering bushes, trees and green grass. Fruit trees are also planted throughout the park and the fruit can be eaten. The park is large and can be easily seen from much of Tijuana's downtown area.

The cost of running this water-treatment center, park and environmental-education area is just US$50,000 per year which includes the salaries of eight people and all operating expenses. As one person touring the park mentioned the massive amount of green space alone would seem to justify the cost of the operation.

Ecoparque has yet to reach completion, however. In the future its operators would like to open a small lake on the site so that phosphates and other material can be cleansed from the water. This third level of treatment would allow the water to be used on crops for human consumption while the lake itself would be used by migrating birds. Finally, Eco-parque would like to be able to treat the few kilograms per day of watery sediment that is left over at the end of the current process. Since a drying bed cannot be located on the site due to its proximity to housing other more costly alternatives will be considered. Currently, remaining sediment mixes with overflow water to the site and is treated in Tijuana's centralized system.

While other people and groups around Tijuana are interested in Ecoparque's water-treatment techniques no one in the city has yet to build a similar structure. However, interest in Ecoparque is not just local. The center is currently used in US college textbooks and US students have come to visit and study the site, according to park administrators. Eco-parque has also received international awards for design and technology and should continue to inspire people into the future.

Contact information for Ecoparque:

Director: Martín Medina
E-mail: elcolefecoparque@ hotmail.com
Phone (from the US): 011-52-66-24-05-31 or 011-52-66-82-00-88

Bloom is editor of Frontera NorteSur, providing on-line news coverage of the US-Mexico border: http://frontera.nmsu.edu. FNS is an outreach program of the Center for Latin American Studies New Mexico State University.

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