Mexico Project Treats Industrial/Municipal Wastewater

Salamanca, Mexico, a city of 500,000 people 130 miles northwest of Mexico City, needed a new municipal wastewater treatment facility to manage its environmental responsibilities. Its biggest industrial asset, an oil refinery and a source of large volumes of wastewater also needed a facility.

Normally, the city and the oil refinery would each have procured its own wastewater plant. However, through cooperation and planning, each solved its needs by combining resources to build a single plant.

Agua Mejor, an engineering-design and construction company headquartered in Guadalajara, Mexico designed the project. Columbian Steel Tank Company provided technology assistance and 20 tanks, which Agua Mejor installed.

The activated-sludge facility has a capacity of more than 310,000 GPD, and today runs at 80% capacity, with two-thirds the flow being from the refinery.

Preceding sludge digestion are an equalization tank and dissolved air flotation (DAF) units for removing oil from the wastewater tank. (The oil mixture is pumped into centrifugal chambers, where gravity separates the oil from the water and polymer.)

Following sludge removal, the water receives calcium carbonate and chlorine treatment. After chlorination, part of the water is recycled back to the refinery for use in the steam system. The remainder goes back to the river that runs through the city.

Indicative of the treatment facility's efficacy is the refinery's exclusive reliance on recycled water for plant use, allowing the refinery to conserve the water from its 38 water wells.

The engineers are said to have specified Columbian tanks for their factory coating, rapid assembly potential without welding equipment and welders, their ease of handling and shipping, and their competitive costs. (Each tank has a corrosive-resistant factory baked-on epoxy coating and an enamel or urethane exterior.)

All tanks are of bolted construction, with concrete pad or steel flooring and open tops. They serve as the clarifiers and digesters, biological reactors, aeration tanks, and dry bulk silos. The largest tank is 130 ft in diameter and 18 ft high. Four are 98 ft by 28 ft, three are 98 ft by 15 ft, and one is 68 ft by 28 ft high. Eleven others are of various sizes.

Each tank was shipped from the manufacturer's Kansas City, KS, plant unassembled in sections, along with all the hardware needed to assemble it at the site. In all, 42 flatbed truck loads traveled to Laredo, TX, where the tanks were unloaded, cleared through customs, reloaded and driven to Salamanca for erection on site.