Léon, Mexico, is an industrial city 400 km north of Mexico City with approximately 1 million inhabitants. It's considered to be the world capital of leather and shoe production. Many worldwide brands such as Adidas and Nike have their products made in its 600 tanneries and 1000 shoe and leather factories, generating tons of wastewater.
Tannery wastewater requires special treatment. Beside organic tanning agents, wastewater from the factories may also contain salts and metals, such as chrome, zirconium, aluminium, titanium and iron, together with synthetic tanning agents such as formaldehyde and phenols.
The original wastewater treatment plant in Léon was previously also used for tannery wastewater, but in the long term proved insufficient for the needs of the developing industrial city. Tannery waste is toxic to most of the facultative bacteria necessary to operate a conventional secondary wastewater treatment facility, so an industrial wastewater treatment plant was needed.
Fypasa and Festo
Fypasa is an engineer-constructor-operator of wastewater treatment plants in Mexico. Fypasa has been building and operating wastewater treatment plants throughout Mexico since 1969 and, therefore, has a great deal of experience as a plant builder. As a plant operator, the company treats 40% of all wastewater in Mexico. The Léon industrial wastewater treatment plant, which Fypasa built in 2009 and has operated ever since, supplements the original treatment plant, which was originally designed for household wastewater. Fypasa understands the construction, operation and maintenance of wastewater plants.
"But, as we are not specialists in plant automation, we rely on the experience of Festo's project engineers," explains Mauricio Plascencia, operations manager of the Fypasa treatment plant in León.
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Festo as System Integrator
Festo, a German company devoted to specialized automation components, developed a complete solution, covering everything from the sensor/actuator level through to the field level, individual control level and process control level, including a SCADA process visualization system. Some of the products were of Festo's manufacture, but many were not.
"Starting with the engineering phase, we supplied Fypasa with a suitable automation concept, including circuit diagrams, CAD data and 3D models of the process valves and control cabinets, central components of the sensor/actuator and field levels, so that they could be included in the designs as ready-to-install units," says Eduardo Poupard, project engineer with Festo Mexico.
Festo was able to demonstrate to Fypasa that it had sufficient experience and understanding of the processes involved in a wastewater treatment plant to develop a solution that meshed perfectly with the plant design.
Festo engineers managed the entire automation project for Fypasa. They handled the purchasing phase with activity charts, definitions of milestones and the punctual delivery of subsystems. The installation phase was simplified by Festo's performing factory acceptance tests (FAT) with simulation tests of the process valves and the control cabinets in the Festo Test Center. Festo also produced the product documentation and completed the installation of subsystems throughout the plant. "This made it easy for us at Fypasa to concentrate fully on our core competencies," Plascencia says. During the commissioning phase, the Festo project engineers conducted site acceptance and process tests (SAT) for each unit within the plant.
How the System Functions
"At the individual control and process control level, the master controller PLC CECX-X-C1 from Festo acts as a programmable logic controller," Poupard says. "It feeds data to the SCADA software VipWin to allow process visualization. CPX/MPA valve terminals gather the input and output signals, feed these to the master PLC and activate the pneumatic actuators. These are installed in seven control cabinets for protection. The automation platform CPX also provides functions for remote maintenance, remote diagnostics, a web server, text messages and an email alarm."
The two fermentation towers are equipped with two types of process valves: gate valves for the sludge inlet and butterfly valves for the fermentation gas discharge. The pneumatic actuators used at the sensor/actuator level to open and close the process valves have significant advantages over electrical installations: durability, long service intervals and safety under overload conditions.